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64th Annual Meeting 
New England intercollegiate 

Geological Cor ference 
1972 

Guidebook 






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for Field Trips 



111 



Vermont 



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UNH LIBRARY 




3 4t,D0 OOSflS 2^31 



New England Intercollegiate Geological Conference 

o4th Annual Meeting 



Guidebook for Field Trips in Vermont 

October 13,14,15, 1972 
Burlington, Vermont 



Editors 

Barry L. Doolan 

Rolfe S. Stanley 

University of Vermont 



University of New Hampshire 
Library 



To Charles G. Doll 

In deepest appreciation of his 
devotion and contributions to 
the understanding of 
Vermont Geology, 
this volume is affectionately 
dedicated by his many 
associates and friends. 




IV 

NEW ENGLAND INTERCOLLEGIATE GEOLOGICAL CONFERENCE 

6 4th Annual Meeting 

Burlington, Vermont 

Sponsors 

University of Vermont Vermont Geological 

Burlington Survey 

Middlebury College Norwich University 

Middlebury Northfield 

Trip Leaders and Authors 

Arden L. Albee , Division of Geological and Planetary Sciences, 
California Institute of Technology. 

Brewster Baldwin, Department of Geology and Geography, Middle- 
bury College. 

Thelma E. Barton, Department of Geology, University of Vermont. 

David P. Bucke, Department of Geology, University of Vermont. 

Parker E. Calkin, Department of Geological Sciences, State Uni- 
versity of New York at Buffalo. 

Peter J. Coney, Department of Geology and Geography, Middlebury 
College. 

G. Gordon Connally, Department of Geological Sciences, State Un- 
iversity of New York at Buffalo. 

Steven L. Dean, Department of Geology, University of Vermont. 

Robert M. Finks, Department of Geology, Queens College, Flushing, 
New York. 

David W. Folger, Department of Geology and Geography, Middlebury 
College. 

Terry K. Frank, Department of Geology, University of Vermont. 

Richard P. Gillespie, Department of Geology, University of Ver- 
mont. 

Roderick Hals ted. Computation Center, University of Vermont. 

David Hawley, Department of Geology, Hamilton College. 

E. B. Henson, Department of Zoology, University of Vermont. 

J. Christopher Hepburn, Department of Geology and Geophysics, 
Boston College. 



Charles C. Howe, Institutional Studies, University of Vermont. 

Allen S. Hunt, Department of Geology, University of Vermont. 

Frederick D. Larsen, Department of General Science, Norwich Uni- 
versity. 

James D. Morse, Department of Geology, University of Vermont. 

William R. Parrott, Department of Geology, Bryn Mawr College. 

Donald B. Potter, Department of Geology, Hamilton College. 

Robert E. Powell, Department of Geology and Geography, Middle- 
bury College. 

John L. Rosenfeld, Department of Geology, University of Califor- 
nia at Los Angeles. 

Arthur C, Sarkisian, Department of Geology, University of Vermont. 

Fred C. Shaw, Department of Geology, Lehman College. 

James W. Skehan, S. J., Department of Geology and Geophysics, 
Boston College. 

Rolfe S. Stanley, Department of Geology, University of Vermont. 

Byron D. Stone, Department of Geography and Environmental Engi- 
neering, The Johns Hopkins University. 

Marilyn E. Tennyson, Department of Geology and Geography, Mid- 
dlebury College. 

George Theokritoff, Department of Geology, Rutgers University. 

James B. Thompson, Jr., Department of Geological Sciences, Har- 
vard University. 

John E. Thresher, Department of Geology and Geophysics, Univer- 
sity of Wisconsin - Madison. 

Donald F. Toomey , Amoco Production Company, Research Center, 
Box 591, Tulsa, Oklahoma. 

Barry Voight , Department of Geosciences, The Pennsylvania State 
University. 

W. Philip Wagner, Department of Geology, University of Vermont. 

Price of guidebook: $4.00 (U.S.) Requests for orders may be 

addressed to: 

Barry L. Doolan or Dabney W. Caldwell, NEIGC 
Geology Department Secretary, Geology Department 
University of Vermont Boston University 
Burlington, Vt. 05401 Boston, Massachusetts 02215 



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NEW ENGLAND 



INTERCOLLEGIATE GEOLOGICAL CONFERENCE 



MEETING PLACES 



Figures refer to yeors in this century 



.08 







Scale of Miles 
50 



100 

—I 



Vll 

NBW ENCUKD INTERCOIXEOI'.TK OEOLOCICAL COWFERKWCE 
CHHONOLOGICAL SUCCESSION OP MEETINGS 



1. 


1901 


?. 


1902 


3. 


1903 


U. 


190^ 


5. 


1905 


6. 


1906 


7. 


1907 


8. 


1908 


9. 


1909 


10. 


1910 


11. 


1911 


12. 


1912 


13. 


1915 


lU. 


1916 


15. 


1917 


16. 


1920 


17. 


1921 


18. 


1922 


19. 


1923 


20. 


192U 


21. 


1925 


22. 


1926 


23. 


1927 


2U. 


1928 


25. 


1929 


26. 


1930 


27. 


1931 


28. 


1932 


29. 


1933 


30. 


193^* 


31. 


1935 


32. 


1936 


33. 


1937 


3^*. 


1938 


35. 


1939 


36. 


19^*0 


37, 


ig'n 


38. 


19^6 


39. 


19'*7 


'♦O. 


igit-s 


1*1. 


19^9 


'♦2. 


1950 


'*3. 


1951 


'f'*. 


1952 


'^S. 


1953 


k6. 


195* 


'^7. 


1955 


i^e. 


1956 


'♦9. 


1957 


50. 


1958 


51. 


1959 


52. 


i960 


53. 


1961 


5*. 


1962 


55. 


1963 


56. 


1964 


57. 


1965 


58. 


1966 


59. 


1967 


60. 


1968 


61. 


1969 


62. 


1970 


63. 


1971 


6*. 


1972 



Westfleld River Terrace, Maes. 

Mo\jnt Tom, Mass. 

West Peak, Meridan, Conn. 

Worcester, Mass. 

Boston Harbour and Nantaaket 

Meriden to East Berlin, Conn. 

Providence, R.I. 

Lon^ Island, N.Y. 

North Berkshires, Mass. 

Hanover, N.H. 

Nahant and Medford, Masa. 

Hlgby-Lanentation Blocks 

Waterbury to Wlnsted, Conn. 

Blue Hills, Mass. 

Gay Head A Martha's Vlnaymrd 

Lamentation & Hanging Hills 

Attleboro, Mass. 

Amherst, Mass. 

Beverly, Mass. 

Providence, R.I. 

Waterville, Maine 

New Haven, Conn. 

Worcester, Mass. 

Cambridge, Mass. 

Littleton, N.H. 

Amherst, Mass. 

Montreal, Quebec 

Providence-Newport, R.I, 

williamstown, Wass. 

Lewiston, Maine 

Boston, Mass. 

Littleton, N.H. 

New York City A Duchess Co, 

Rutland, Vt, 

Hartford & Conn. Valley 

Hanover, N.H. 

Northampton, Mass. 
Mt, Washington, N.H. 
Providence, R.I. 
Burlin,^ton, Vt, 
Boston, Mass. 
Bangor, Maine 
Worcester, Mass, 
Wllliamstown, Mass. 
Hartford, Conn. 

Hanover, M,H, 

Tieonderoga, N.Y, 
Portsmouth, N.H, 

Amherst, Mass, 

Middletown, Conn, 

Rutland, Vermont 

Rumford, Me, 
Montpelier, Vt. 

Montreal, Quebec 

Providence, R.I, 

Chestnut Mill, Mssa, 
Brunswick, M«, 
Katahdin, He. 
Amherst, Mass, 
New Haven, Conn, 
Albany, H.y, 
Ran^eiey Lakes, M«, 
Concord, N.H. 
Burlington, Vt, 



Davis 

Emerson 

Rice 

Emerson 

Johnson, Crosby 

Gregory 

Brown 

Barrall 

Cleland 

Goldthwalt 

Lane, Johnson 

Rice 

Barrall 

Crosby, Warran 

Woodworth, Wigglssworth 

Rice, Foye 

Woodworth 

Antevs 

Lane 

Brown 

Perkins 

Longwell 

Perry, Little, Gordon 

Billings, Bryan, Mather 

Crosby 

Loomis, Cordon 

O'Neill, CrahMB, Clark, Cill, Osborne, 

McGerrigl* 

Brown 

Cleland, Perry, Knopf 

Fisher, Perkins 

Morris, Pearsall, Whitehead 

Billings, Hadley, Cleaves, Willisus 

O'Coratell, Kay, Fluhr, Hubbert, Balk 

Bain 

Troxell, Flint, Loncirell, Peoples, Wheeler 

Goldthwalt, Denny, SiMMb, Hadley, Bannervan, 

Stoiber 

Balk, Jahns, Lochman, Shaub, Willard 

Billings 

Quinn 

Doll 

Nichols, Billings, Sctirock* Currier, Steams 

Trefethen, Raisz 

Lotigee, Little 

Perry, Foote, McFadyen, Ramsdell 

Flint, Gates, Peoples, Cushaan, Altken, 

Bodgers, Troxell 

Elston, Washburn, Lyons, MeKlnstry, 

Stoiber, KcNair, Thompson 

Rodgers, Walton, MacClintock, Bartoloae 

Novotny, Billings, Chapman, Bradley, 

Preedwan, Stewart 

Bain, Johannson, Rice, Stobbe, Woodland, 

Brophy, Kierstead, Webb, Shaub, Nelson 

Rosenfeld, Eaton, Sanders, Porter, 

Longren, Rodgers 

Zen, Kay, Welby, Bain, Theekritoff, 

Osberg, Shuaaker, Berry, Thoapson 

Grlscom, Milton, Wolfe, Calwell, Peaeer 

Doll, Cady, White, Chidester, Matthews, 

Nichols, Baldwin, Stewart, Dennis 

Gill, Clark, Kranek, Sterensen, Steam, 

Elson, Eakins, Cold 

Quinn, Mutch, Schafer, Agren, Chappie, 

Feinin^er, Hall 

Skehan 

Huesey 

Caldwell 

Robinson, Drake 

Orville 

Bird 

tioone 

Lyons, Stewart 

Doolan, Stanley 



IX 



TABLE OF CONTENTS 

page 

Dedication to Charles G. Doll iii 

Conference Organization iv 

Forward and Acknowledgments xiii 

Bedrock Geology Trips 1 

B-1. Stratig raphy of the East Flank of the Green 
Mountain AnticTinorium ^ SoutherrT^ermont . 
James W, Skehan, S.J. and J. Christopher 
Hepburn 3 

B-2. Major Structural Features of the Taconic 
Allochthon in the Hoosick Falls Area, New 
York - Vermont . ^ 

Donald B. Potter 27 



B-3. Excursions at the North End of the Taconic 
Allochthon and the Middlebury Sy nclmorium y 
West-Central Vermont ^ with EmpFas is on tTTe 
Structure of the Sudbury Nappe and Associat- 
ed ParautocEthonous Elements . 
Barry Voight 



\^ 



B-4. The Cham p lain Thrust and Related Features 
near~Mr?dlebury , Vermont . 
Peter J. Coney, Robert E. Powell, Marilyn 
E. Tennyson, and Brewster Baldwin ^^ 



49 



B-5. Analysis and Chronology of Structures along 
the Cham p lain Thrust West of the Hinesbur g 
Sy nclinorium . 
Rolfe S. Stanley and Arthur Sarkisian ^^^ 

B- 6 . Sedimentary Characteristics and Tectonic 

Deformation of Middle andl jpper OrdovicTan 

Shales of Northwestern Vermont North of 

Malletts Bay. 

David Haw ley ^^^ 

B-7. Rotated Garnets and Tectonism in Southeast 
Vermont. 
John L. Rosenfeld 16'7 

B-8. Strati g ra p hic and Structural Relationshi ps 
across the Green Mountain Anticlinorium in 
North - Central Vermont . 
Arden L. Albee I'^S 



B-9. Sup er p osed Folds and Structural Chronolo gy 

alon g the Southeastern~Part of~the Hinesbur g 

Sy nclinorium . 

Richard P. Gillespie, Rolfe S. Stanley, 

Thelma E. Barton, and Terry K. Frank 195 

B-10. Lower Paleozoic Rocks Flankin g the Green 
Mountain Anticlinorium . 
James B. Thompson, Jr. 215 

B-11. Geology of the Guilford Dome Area , South- 
eastern Vermont . 
j"I Christopher Hepburn 231 

B-12. Stratigra p hic and Structural Problems of the 
Southern Part of the Green Mountain Anti - 
clinorium , Bennington-WiTinin g ton , Vermont . 
James W. Skehan, S.J 245 

B-13. Polymetamor p hism in the Richmond Area , Ver - 
mont . 

John E. Thresher. (Complete text will be 
available at the N.E.I.G.C. meeting in Bur- 
lington. ) 269 

Environmental Geology Trips 271 

EG-1. Mount Mansfield Trail Erosion . 

Roderick HalstedT ^Complete text will be 
available at the N.E.I.G.C. meeting in Bur- 
lington. ) 273 

EG-2. Feasibility and Desi gn Studies ; Cham p lain 
Valley Sanitary LandfTll . 
W. Philip Wagner and Steven L. Dean 277 

Glacial Geology Trips 295 

G-1. Glacial History of Central Vermont . 

Frederick D. Larsen i 296 

G-2. Ice Mar g ins and Water Levels in Northwestern 
Vermont . 
W, Philip Wagner 317 

Pro g lacial Lakes in the Lamoille Valle y, 

Vermont. 

G. Gordon Connally 343 

Roadlog for Trip G-2 352 



XI 



G-3. Strandline Features and Late Pleistocene 
Chronolo gy of NortlTwest Vermont . 
William R. Parrott and Byron D. Stone 359 

G-5. Till Studies y Shelburne, Vermont . 

W. Philip Wagner, James D. Morse, Charles 

C. Howe 377 

G-6. Woodfordian Glacial History of the Cham- 
p lain Lowland , Burlin g ton to Brandon , Ver- 
mont . 
G. Gordon Connally and Parker E. Calkin.... 389 

Lake Studies Trips 399 

LS-1. The Slud ge Bed at Fort Ticonderoga, New 
York . 
David W. Folger 401 

LS-2, LS-3. Sedimentolo g ical and Limnolo g ical 
Studies of Lake Cham p lam . 
Allen S. Hunt, E.B. Henson, and David P. 
Bucke 407 

Paleontology Trips 427 

P-1. Qrdovician Paleontolo gy and Strati g rap hy of 
the Cham p lain Islands . 
R.M. Finks, F.C. Shaw, and D.F. Toomey 429 

Paleontology and Strati graphy of the Chazy 
Grou p ( Middle OrdovicianT T Champlain , Is- 
lands , Vermont . 
F.C. Shaw 429 

Paleoecolo gy of Chazy Reef -Mounds . 

Robert M. Finlci" and Donald F. Toomey 443 

P-2. Cambrian Fossil Localities in Northwestern , 
Vermont. 
George Theokritof f 473 

Appendix 479 



XlLl 



FORWARD 



"Largely through. ... (the publi- 
cation of) the new geologic map 
of the state, a widespread active 
interest has been created among 
geologists who will come to Ver- 
mont to study and make comparisons 
with the geology of already classic 
areas elsewhere." (Doll, 1962, p. 11) 



These words written by Charles G. Doll in the 1960-62 
Biennium Report of the State Geologist were published a year 
after the last meeting of the N.E.I.G.C. in Vermont, a meeting 
hosted by the Vermont Geological Survey in celebration of the 
publication of the Centennial Geologic Map of Vermont, 

Charles Doll's perceptive insights of the impact of the 
new map on the geologic community have proven to be modestly 
correct. In the eleven years since the publication of the Cen- 
tennial Map, Vermont geology has been undergoing active reexam- 
ination to answer the seemingly never-ending problems of the 
complex geologic history of the northern Appalachians and, more 
recently, to relate Vermont to the history of continental drift 
and plate tectonics in the North Atlantic. 

Also, in the last eleven years, through the effort of 
Charles Doll, the Vermont Geological Survey has initiated and 
completed a surficial mapping program culminating in the publi- 
cation of the Surficial Geologic Map of Vermont in 1970, and 
initiated an Environmental Geology mapping program actively in 
progress for the past two years. 

With these accomplishments and activities clearly in mind, 
the editors, the many guidebook contributors, and numerous work- 
ers have striven to compile a guidebook which reflects the diver- 
sity of subject and areal extent of Vermont's complex geology. 

In meeting these goals and in anticipation of active parti- 
cipation of large numbers of professionals, students, and teach- 
ers at this conference, a record number of trips have been organ- 
ized (24) in Bedrock Geology, Environmental Geology, Glacial Geol- 
ogy, Lake Studies, and Paleontology. These trips have been alpha- 
betically arranged under the appropriate headings in the following 
pages for ease of reference and continuity of subject matter. 



XIV 



To accommodate more active participation by all those 
attending the conference, the editors sought (and gratefully 
received) cooperation from the contributors to publish the guide- 
book ahead of schedule so that it can be in the hands of partici- 
pants before they attend the conference. Since many of these 
participants will be students and professionals unfamiliar with 
many aspects of Vermont geology, we have compiled in the immedi- 
ately following introductory pages, pertinent maps and tables 
from Vermont Geological Survey publications for their perusal. A 
complete listing of Vermont Geological Survey publications is ap- 
pended at the rear of this guidebook for those wishing to obtain 
additional, more complete information on various aspects of Ver- 
mont geology before the conference. 

By including all this material under one cover to supple- 
ment the very fine array of papers by the contributors we sincere- 
ly hope that this guidebook will also be of use to high schools, 
laymen, and many university-organized field trips in the years to 
come. 

Acknowledgements 

With pleasure we gratefully acknowledge the significant con- 
tributions, generous suggestions and efforts of the field trip 
leaders and authors. The early publication of a guidebook with 
thirty-six contributors, nearly 500 pages, and twenty-four field 
trips is indeed a tribute to their cooperation. A great deal of 
this credit however must also go to two extremely dedicated indi- 
viduals who prepared the papers for publication, handled the num- 
erous logistical problems, and offered many suggestions. Margaret 
Newton, department secretary, proofread the entire guidebook and 
typed most of its pages. Terry Frank, our "NEIGC secretary" com- 
pletely revamped the NEIGC mailing list, organized the trip lists 
and handled all the correspondence and finances of this conference. 
To both of them thanks for a job well done ! Miscellaneous draft- 
ing chores and preparation of many of the guidebook figures by 
Sally Rising and Thelma Barton, University of Vermont geology stu- 
dents, are also gratefully acknowledged. 

Special thanks go to Art Huse of the UVM Geology Department 
for printing and layout of the "chapter headings" of this guide- 
book. 

Finally we acknowledge John Wiley and Sons for permission 
to reproduce Figures 14-1 , 14-5 and Table 14-1 from Zen, E. and 
others. Studies of Appalachian Geology ; Northern and Maritime, 
for John Rosenf eT5' s trip (B-7) , and the Vermont Geological Survey 
for permission to print figures, maps, and tables from earlier 
publications. 

This guidebook has been printed and bound by the University 
of Vermont Print Shop. 

Barry L. Doolan 
Rolfe S. Stanley 
Department of Geology 
University of Vermont 
Editors 



XV 




HELD TRIP LOCALITIES 
1972 N.E.I.G.C. 64 th ANNUAL MEETING 
BURLINGTON. VERMONT 

LEGEND 

• Bedrock 
a Environmental 
■ Glacial 
' Lake Studies 

• PaleontoloBy 

1-3 Field trip number 
and stop number 



10 13 ao 

MILES 



XVI 



QUEBEC-CANADA 




WILLIAMS ; NORTH 
TOWN I ADAMS 

MAlsSACHiusriTlfe 



! B E R L /N TOWN I ADAMS I ROWE 1 HEATH COLRAIN 

/ 



EDITING 
^^^H w M Cady 




C G Doll 








J B Thompson, Jr 


General: 


M. P. Billings 



INDEX MAP OF VERMONT 

Shows quadrangle grid, sources of primary geologic information, and 

(on inset map) areas of regional geologic studies and ot editorial responsibility 

from: Centennial Geologic 
Map of Vermont. 
(Doll, et al. , 1961) 



XVI 1 




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XVlll 



QUEBEC-CANADA 




MASSACHUSETTS 

METAMORPHIC MAP of VERMONT 



METAMORPHIC ZONES 
EXPLANATION 



Posl MBi»iti..fD(ilr tiult4 








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MuM ^ a™. «»|* 

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III! 

LO MoHa 




Adapted from the Centennial Geologic Map ol 
Vetmont by Chatlei G. Doll, Stole Geologist. 




bedrock geology 




*S«k.*. 



Bedrock Geology Cover page: Upper: Champlain overthrust at Rock 
Point, Lake Champlain, Vermont; see Stanley and Sarkisian (Trip 
B-4, this guidebook). Photo by Terry Frank. Lower left: De- 
tail of flow structure at the hinge of Scotch Hill syncline with- 
in dolostone bed (actual size approximately 1.5 x 2 inches). See 
Locality 2, Trip B-3; Barry Voight (this guidebook). Lower right: 
Shelburne fishing access area, Shelburne, Vermont; detail of sin- 
istral fault and associated fractures; see Stanley and Sarkisian 
(Trip B-4, this guidebook). 



Trip B-1 

STRATIGRAPHY OF THE EAST FLANK OF THE 
GREEN MOUNTAIN ANTICLINORIUM, SOUTHERN VERMONT 

by 

James W. Skehan, S.J.* and J. Christopher Hepburn* 

INTRODUCTION 

The Green Mountain anticlinorium in southern Vermont has an 
exposed core of Precambrian gneisses overlain to the east and 
west by metamorphosed Paleozoic rocks. The rocks of the west 
limb of the anticlinorium are chiefly quartzites and carbonates 
of a miogeosynclinal sequence. The east limb of the anticlinorium 
consists of a eugeosynclinal sequence of schists and gneisses 
from (?) Cambrian through Lower Devonian age. The purpose of the 
present field trip is to examine the stratigraphy of these schists 
and gneisses. A roughly west-to-east section across portions of 
the Wilmington and Brattleboro quadrangles (Fig. 1) will be 
followed. 

The earliest geological mapping in the area was done by 
E. Hitchcock and others during the compilation of the Geology of 
Vermont (E. Hitchcock et al., 1861). Hubbard (1924), Prindle and 
Knopf (1932) , Richardson TT933) , and Richardson and Maynard (1939) 
studied portions of the area. Thompson (1950) and Rosenfeld (1954) , 
working in the Ludlow and Saxtons River quadrangles respectively, 
started the comprehensive detailed mapping of southern Vermont. 
Detailed geological mapping of the field trip area has been com- 
piled by the authors (Fig. 1). The Wilmington-Woodf ord area was 
mapped by Skehan (1953, 1961), and the Brattleboro area by 
Hepburn (1972b) . 

Most of the stratigraphic units of the east limb of the Green 
Mountain anticlinorium in southern Vermont can be traced directly 
from the Wilmington-Brattleboro area to their type localities 
further north in Vermont or to the south in Massachusetts. A 
few can be traced into f ossilif erous strata. Currently a number 
of workers (see for example Hatch, Osberg , and Norton, 1967; 
Hatch, 1967; Hatch, Schnabel and Norton, 1968) are tracing many 
of these units and their correlatives southward through western 
Massachusetts and western Connecticut. 



*Department of Geology and Geophysics 
Boston College 
Chestnut Hill, Massachusetts 02167 



STRATIGRAPHY 

The stratigraphy of the field trip area is briefly summarized 
below. See Skehan (1961) and Hepburn (1972b) for more complete 
descriptions . 

Wilmington Gneiss 

The Wilmington Gneiss named by Skehan (1961) is of uncertain 
stratigraphic position. It may be Precambrian in age, resembling 
as it does the microcline gneiss sequence of the Mt. Holly Com- 
plex of the Green Mountain core. On the other hand the apparently 
conformable relationship immediately beneath the Hoosac and 
Tyson Formations along their eastern contact (Fig. 1) suggests 
strongly the possibility that the Wilmington Gneiss may be of 
Cambrian age. The complex and unexplained relationships of the 
Wilmington Gneiss to the members of the Cavendish Formation of 
Doll et al^. (1961) along the western contact make a decision as 
to the age of the Wilmington Gneiss impossible at this time. 

The Wilmington Gneiss consists of a medium to very coarse- 
grained, well-banded, somewhat foliated biotite-epidote-quartz- 
microcline augen gneiss. The microcline is gray to pink and 
occurs as lenticular augen and flaser in which the average 
long diameter is about 7mm. Locally the augen may reach 8 in. 
in length and are usually flattened into the plane of the folia- 
tion. Quartz rods and linearly aligned streaks of biotite are a 
common feature of the Wilmington Gneiss. 

The Wilmington Gneiss may be the correlative of the Bull Hill 
Gneiss of Doll et al. (1961) , an exposure of which is only one 
mile north of and on line with the northernmost exposure of the 
Wilmington Gneiss of the Wilmington quadrangle (Skehan, 1961, PI. I) 

Tyson Formation 

The Tyson Formation, named by Thompson (1950), is recognized 
in this area only as discontinuous lenses of fine to coarse- 
grained, schistose, white to blue quartz-pebble conglomerate; 
fine to coarse-grained gray, buff and pink microcline-pebble and 
coarse-grained albite-pebble conglomerate and conglomeratic schist; 
and thin-bedded quartzite and dark biotite-muscovite-quartz schist. 



Hoosac Formation 



The Hoosac Formation (Hoosac Schist of Pumpelly et a_l. , 1894) 
consists of gray, brown and black, mediiom to coarse-grained 
muscovite-biotite-albite-quartz schists locally containing variable 
amounts of chlorite, muscovite, paragonite and garnet. Rocks con- 
taining appreciable garnet commonly weather to a mottled rusty 
color. Albite megacrysts 2-15 mm. in diameter are characteristic 
of the formation, which is distinguished from the overlying 
Pinney Hollow Formation by the presence of more abundant albite 
megacrysts, its color, and its generally coarser and more granular 
texture. 

The Turkey Mountain Member of the Hoosac Formation (named by 
Rosenfeld, 1954) is typically a dense dark green to black amphibo- 
lite commonly characterized by rounded to sub- angular white, gray, 
green or dark brown "amygdules" composed of quartz and albite 
commonly with included epidote, hornblende and garnet. 

Pinney Hollow Formation 

The Pinney Hollow Formation named by Perry (1928) is character- 
istically a pale to dark green well-foliated chlorite-muscovite- 
(paragonite) -chloritoid-garnet-quartz schist. Epidote-albite- 
hornblende amphibolite including amygdaloidal amphibolite is 
interbedded with the chlorite schist. 

The Chester Amphibolite named by Emerson (1898b) and mapped 
as a separate formation by Skehan (1961) , is here considered as 
a member of the Pinney Hollow Formation, following the usage of 
Doll et al. (1961) . The Chester Amphibolite is mapped as the 
first thick sequence of amphibolites above the dominantly green 
Pinney Hollow chlorite schists and immediately below the black 
schists of the Ottauquechee Formation, 

The Chester Amphibolite is characteristically a banded, well- 
foliated epidote-chlorite-albite-hornblende schist containing thin 
beds of dark gray to black muscovite-quartz schist and green 
ch lor ite-muscovite- gar net-quartz schist. 





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Ottauquechee Formation 

The Ottauquechee Formation named by Perry (1928) is character- 
istically a rusty-weathering uniform sequence of black sulfide- 
bearing, muscovite-garnet- (chlorite) -quartz schist; sulfide- 
bearing feldspathic quartzite and vitreous black quartzite; and 
feldspathic biotite-quartz schist. 

Stowe Formation 

The Stowe Formation named by Cady (1956) is identical to 
the Pinney Hollow Formation proper. In the northern part of the 
Wilmington quadrangle a thick amphibolite unit similar to the 
Chester Amphibolite forms the base of the sequence and has been 
mapped separately (Osa) . 

Missisquoi Formation 

Following Doll et al. (1961) the Missisquoi Formation con- 
sists of the rocks lying between the Stowe Formation and the 
Ordovician-Silurian unconformity at the base of the Shaw Mountain 
Formation. It is continuous from the Wilmington-Brattleboro area 
to northern Vermont where it was defined as the Missisquoi Group 
by Richardson and Cabeen (1923) . The Missisquoi Formation is 
subdivided into three members. 

More town Member 



The Moretown Member, defined by Cady (19 56) as the More town 
Formation, is characterized by distinctive interlayered quartz- 
mica schists, mica schists, and quartz-rich granulites. Typically, 
light gray granulites and quartz-rich schists are interlaminated 
with light to dark gray micaceous laminae on a scale of 2 mm. 
to a few centimeters in thickness. Where the lamination is con- 
tinuous and abundant on a fine scale, the rock has a distinctive 
"pinstriped" appearance. At least some of the thin interlayering 
of the micaceous bands is of secondary origin. Garnet and chlorite 
porphyroblasts are common and pyrite cubes as large as 1.5 cm. 
are not an uncommon accessory. Fasciculitic chlorite and biotite 
sprays after an amphibole are seen on some schistosity surfaqps. 
Interlayers of amphibolite and garnet amphibolite account for up 
to 20 percent of the member. 



SYSTEM 



Wilmington- 
Brattleboro 
Area 



Western Mass. 
(Hatch et^ al. , 
1968 and 1970) 



Western Mass. 
(Emerson, 1898a, 
1898b, and 1917) 



New Hampshire 
(Billings, 1956; 
Thompson e_t al . , 
1968) 



Gile Mountain Fm. 



Waits River 
Formation 



Leyden Arglllite 



Littleton 
Formation 



DEVONIAN 



o 



Putney Volcanics 
_"» > ?— ?- 

Standing Pond Vol. 



Waits River Fm. 




Conway Amphib 



00 u 
c 0) 



Conway Schist 



SILURIAN 



Northfield 
Formation 



Goshen Formation 



Fitch Formation 



Shaw Mt. Fm. 



Russell Mt. Fm. 



Goshen Schist 



Clough Quartzite 



ORDOVICIAN 



o 
to 



Cram Hill Mbr. 



Barnard 

Volcanics 

Member 



Partridge Fm. 



Hawley Formation 



Hawley Schist 



Ammonoosuc Vol. 



Moretown 
Member 



Moretown 
Formation 



Albee Formation 



Stowe Formation 



Savoy 
Schist 



CAIIBRIAN 



Ottauquechee Fm. 



Rowe Schist 



I Chester Amphib 
Pinney Hollow Fm. 



Chester Amphib. 



Rowe Schist 



Hoosac Formation 



Hoosac Fm. 



Hoosac Schist 



? CAMBRIAN 



w 

•H 

c 
> 



Heartweilviile 



Readsboro 



Sherman Marble 
Searsburg Cgl. 



Wilmington Gn. 



PRECAMBRIAN 



Mt. Holly Complex 
Stamford Granite 
Gneiss 



Stamford Granite 
Gneiss 



Becket Gneiss 



Figure 2. Correlation Chart of the VJilmington-Brattleboro Area, Vermont. 



10 



Barnard Volcanic Member 

The Barnard Volcanic Member includes a wide variety of 
rocks, but three general types are most abundant: non-porphyri- 
tic amphibolite; porphyritic amphibolite with numerous feldspar 
megacrysts; and light-colored, felsic schist and gneiss. The 
felsic rocks make up 35 to 50 percent of the member. 

Cram Hill Member 

The Cram Hill Member, first designated as the Cram Hill 
Formation by Currier and Jahns (1941) , is correlative with 
fossiliferous late Middle Ordovician rocks at Magog, Quebec 
(Berry, 1962) . The member consists largely of fine-grained 
black phyllite and schist that weathers a rusty-brown from 
finely disseminated pyrite or pyrrhotite. Thin, fine-grained, 
black quartzite beds are not uncommon. Biotite and pyrite are 
the common porphyroblasts , and garnet may be present. Thin 
amphibolite layers are common. A zone at the top of the member 
in which amphibolite predominates has been separated on Figure 1 
as Omcha . 



Shaw Mountain Formation 



In the Brattleboro quadrangle the Silurian Shaw Mountain 
Formation (Currier and Jahns, 1941) occurs in only three thin 
lenses to the east of the regional unconformity at the top of 
the Missisquoi Formation. White to light brown weathering 
quartzite and quartz-pebble conglomerate occur at the base of 
the formation. These rocks grade upward into quartz-mica schist, 
mica schist, a coarse-grained hornblende fasciculite schist, and 
amphibolite . 

Northfield Formation 

The Northfield Formation, named the Northfield Slate by 
Currier and Jahns (1941) , is a uniform sequence of gray to dark 
gray, graphitic quartz-muscovite schists with very conspicuous 
almandine porphyroblasts 1 to 2 mm. in diameter. Biotite is a 
common additional porphyroblast , as is staurolite at the appro- 
priate grade. Crinkle lineations are commonly well developed in 
the schists. Thin quartzite beds are occasionally present but 
are not as abundant as they are along strike in the Goshen Forma- 
tion of western Massachusetts (Hatch et al. , 1968) . A few punky- 
brown weathering impure marble beds similar to those in the over- 
lying Waits River Formation are present. 



11 



Waits River Formation 



The Waits River Formation (Currier and Jahns , 1941) con- 
sists of interbeds of three broad categories of rocks: impure 
marbles, various schists, and impure quartzites. The most dis- 
tinctive rocks are the impure marbles, which weather to a punky- 
brown and have a friable surficial rind of non-calcareous minerals, 
largely quartz, left behind where the carbonate has weathered out. 
The impure marbles occur in beds a few inches to tens of feet 
thick. The percentage of these beds varies throughout the forma- 
tion. 

The schistose rocks are quite variable but generally weather 
dark gray to brown and contain quartz and muscovite with differing 
amounts of biotite, garnet, or carbonate. Zoisite may be an 
additional porphyroblast . 

Thin beds of light gray feldspathic and micaceous quartzite 
occur throughout the formation. A narrow band adjacent to the 
Standing Pond Volcanics has been separated (Dwrq, Fig. 1) in 
which the impure quartzites are present to the exclusion of the 
other rocks. 



Standing Pond Volcanics 

The Standing Pond Volcanics (Doll, 1944, Standing Pond 
Amphibolite) consist mostly of black, massive to moderately 
foliated amphibolite and epidote amphibolite. Very coarse- 
grained garnet amphibolite is commonly present near the contact 
with the Waits River Formation. Minor amounts of brown-weathering 
schist, feldspathic quartzite and coticule are also present. The 
eastern band of the Standing Pond Volcanics (Fig. 1) is composed of 
plagioclase-biotite-quartz and plagioclase-biotite-hornblende- 
quartz granulite. 

Gile Mountain Formation 

In the area to be visited by this field trip the Gile Mountain 
Formation (Doll, 1944, Gile Mountain Schists) is metamorphosed to 
the kyanite-staurolite zone. At this grade of metcunorphism the 
principal rocks in the Gile Mountain Formation are micaceous and 
feldspathic quartzites and mica schists. The quartzites weather 
light gray and contain variable amounts of quartz, feldspar, 
muscovite, and biotite. Garnet, hornblende, and ankerite are 
present in minor amounts. Kyanite, staurolite, and garnet 
porphyroblasts are common in the mica schist interbeds. 



12 



STRUCTURE 

The axial trace of the regional Green Mountain anticlinorium 
(Skehan, this volume, Sunday Trip, Figs. 1 and 3) lies just to 
the west of the field trip area. Most of the units seen on the 
field trip dip moderately to steeply east and are part of the 
homoclinal sequence of the east limb -of the anticlinorium (Fig. 1) . 
The Lower Cambrian miogeosynclinal facies, well-developed on the 
western limb of the anticlinorium, can be traced to its southeast 
limb, where it appears to be cut off by the Hoosac thrust fault. 
The (?) Cambrian Cavendish Formation in the southern part of the 
area overlies these Lower Cambrian rocks and the Precambrian 
core as a result of westward thrusting. In the northern part 
of the area, the Cavendish may be separated from the Precambrian 
by an angular unconformity or by the continuation of the Hoosac 
thrust. Overlying the Cavendish Formation is the Cambrian and 
Ordovician sequence of metasediments and metavolcanics . The 
Lake Rayponda and Sadawga Pond domes (Fig. 1) have locally dis- 
rupted the eastern limb of the anticlinorium. 

The Guilford dome lying east of the Green Mountain anti- 
clinorium is part of a belt of domes that stretches from central 
Vermont to Connecticut, west of the Connecticut River. The 
Chester and Athens domes, just north of the field trip area, 
have exposed Precambrian rocks in their cores. The Siluro- 
Devonian Waits River Formation is exposed in the center of the 
Guilford dome. Large recumbent folds are present in the strata 
mantling these domes in eastern Vermont. The doubly-closed loop 
of the Standing Pond Volcanics (Fig. 1) outlines such a fold, the 
Prospect Hill recumbent fold. This recumbent fold had formed 
prior to the doming and had a NE-SW trending axis. The sub- 
sequent doming arched the axial surface of the recumbent fold, 
causing the hinges to plunge moderately NE and SW away from 
the roughly N-S axial trace of the dome. 

A sequence of at least four minor fold stages (Hepburn, 1972a) 
has been worked out for the eastern portion of the field trip area. 
The following sequence of minor folds is inferred: 

(1) Small isoclinal folds with a schistosity developed 
parallel to their axial surfaces. 

(2) Tight to isoclinal folds related to the Prospect Hill 
recumbent fold. A schistosity is developed parallel 
to the axial surfaces of these folds in some of the 
metapelites . 



13 



(3) Open folds with a slip-cleavage developed parallel 
to their axial surfaces. This cleavage generally 
strikes northeast and dips moderately to steeply 
northwest. These folds may have formed during the 
development of the Guilford dome. 

(4) One or more generations of open folds, warps, or 
buckles in the foliation that fold the slip-cleavage. 

Metamorphism 

The area was regionally metamorphosed during the Acadian 
Orogeny. At this time the Precambrian rocks in the exposed 
core of the Green Mountain anticlinorium, previously metamorphosed 
to a high degree during the Grenville Orogeny, were extensively 
retrograded. The rest of the field trip area was metamorphosed 
to the garnet zone, except for the Guilford dome where the 
staurolite-kyanite zone was reached, as seen at the last two 
stops. 



1^ 



Road Log for Trip 
Friday, October 13, 1972 

James W. Skehan, S.J. and J. Christopher Hepburn, Leaders 

Primary references for this trip are: 

Doll, et_ al^. , (1961) Centennial Geologic Map of Vermont , 
October, 1961 ($4.00). 

Hepburn, J.C. (1972b) Geology of the Metamorphosed Paleozoic 

Rocks in the Brattleboro Area, Vermont , unpub . Ph.D. Thesis, 
Harvard University, 377 p. 

Skehan, J.W., S.J. (1961) Geologic Map of the Wilmington- 
Woodford Area , from Bulletin 17, Vermont Geological 
Survey (25<;:) 

Skehan, J.W., S.J. (1961) The Green Mountain Anticlinorium in 

the Vicinity of Wilmington and Woodford, Vermont , Bulletin 17, 
Vermont Geological Survey, 159 p. ($3.00) 

All references, except Hepburn (1972b) may be obtained from the 
State of Vermont, Department of Libraries, Montpelier, Vermont. 
Enclose payment with order. 

Mileage 

0.00 Assemble at the junction of Routes 9 and 100, 1.15 miles 
east of the center of Wilmington, Vermont in the parking 
lot of Coombs' Beaver Brook Sugar House (Fig. 1). Park 
south of tne store out of traffic. West of Route 100 
at this locality, large outcrops of Wilmington Gneiss 
can be seen and may be examined by those arriving early. 

Departure time at 8:45 a.m. SHARP . Proceed to Stop 1 by 
going south on Route 100. 

0.85 Turn left and proceed up the hill to Hubbard Hill Farm. 

1.35 Stop 1 . WILMINGTON GNEISS, TYSON AND HOOSAC FORMATIONS. 

Park off the unpaved road near the farm buildings of 
Hubbard Hill Farm. To the northwest one may see the 
Wilmington Valley and the Haystack-Mount Snow Ridge. 
Proceed on foot uphill to the northeast toward the crest 
of the hill. The outcrops west of the hillcrest are 
those of the micaceous microcline augen Wilmington Gneiss. 
At this locality, between the well-developed Wilmington 
Gneiss and the typical micaceous albite schists of the 



. 



15 



Mileage (cont'd) 

Hoosac Formation, is a blue-quartz-bearing gneiss and 
schistose gneiss assigned to the Tyson Conglomerate 
(Skehan, 1961, pp. 65-66). 

The structure is dominated by cascade folds in which 
the movement sense is such that the upper beds have 
moved easterly relative to the lower beds. Some out- 
crops on the eastern flank of this hill show well- 
developed cascade folds with amplitudes of 1 1/2 feet. 
Although a number of individual outcrops show shallow 
to steep westerly dips, the beds have an average dip 
to the east. The axial planes of the cascade folds 
dip at an average of 50° NW, Return to cars, turn 
around, and return 0.4 5 mile to Route 100. 

1.75 Proceed south on Route 100. 

1.77 Outcrops of rusty weathering, dark albite schist of the 
Hoosac Formation underlain by banded plagioclase gneiss 
of the Wilmington Gneiss on the east side of the highway. 

1.95 Turn right off Route 100 south at the Dix School. 

Proceed southwest on Boyd Hill Road. This road crosses 
terrain underlain by the micaceous microcline augen 
gneisses of the Wilmington Gneiss Formation. 

3.35 Stop 2. HOOSAC FORMATION, TURKEY MOUNTAIN MEMBER AND 

WILMINGTON GNEISS. 

Park off the road wherever you can near two houses on 
the left and the barn on the right. Proceed to the hill 
by a path between the two houses. Climb up the hill 
examining the Wilmington Gneiss in the lower ledges. The 
albite schist sequence of the Hoosac Formation and the 
amphibolites of the Turkey Mountain Member of the Hoosac 
are exposed in the upper ledges and constitute an outlier 
of Cambrian rocks surrounded by Wilmington Gneiss. Return 
to the cars and proceed north. 

3.60 On the west side of the road, outcrops of Wilmington Gneiss 
dip gently to the northwest at 15°. There is a strong 
quartz rodding and biotite lineation nearly down the dip. 

Proceed north to the end of Boyd Hill Road. 

5.20 Turn right and proceed to Wilmington Center (0.45 mile). 



16 



M ileage (cont'd ) 

5.65 At the lights in Wilmington Center, turn right (east) 
on Route 9 . 

6.35 On the hill to the north are rusty weathering, albite 
schists dipping gently to the north toward the center 
of the Wilmington syncline. 

6.80 Coombs' Sugar House where the field trip began. Late- 
comers may join the trip at this time (approximately 
10:15 a.m.) and place. Continue east on Route 9. 

7.10 Turn left at the NAJEROG sign and proceed 0.4 mile along 
an unpaved road (the original Molly Stark Trail) . 

Stop 2a. TURKEY MOUNTAIN MEMBER 

Park at a white house and barn belonging to Mr. and Mrs. 
Donald Koelsch. Go up the hill to the west, observing 
the Turkey Mountain Amphibolite Member and the overlying 
sequence of albite schists of the Hoosac Formation 
(Modes of the Hoosac Formation are in Tables 15-19, 
p. 68 Skehan, 1961) . Proceed to the top of the hill 
where you may observe recumbent folds in the albite schist 
and the development of small-scale microcline pegmatites. 
Structural analysis indicates that the sense of movement 
of the upper beds is toward the east relative to the 
lower. Such folds have been described by Skehan (1961, 
p. 103) as cascade folds. They are commonly well 
displayed in association with the Sadawga Pond dome and to 
a lesser extent with the Lake Rayponda dome. Commonly 
throughout southern Vermont such minor folds are late 
structures and are selectively better developed on the 
eastern flanks of the domes. The fact that the cascade 
folds seem not to be equally well developed on all sides 
of the dome calls into question Skehan' s (1961) and 
Thompson's (1950) earlier conclusion that these folds 
are a product of the doming. Such cascade folds as seen 
at Stop 1 may, however, be related antithetically in some 
as yet unexplained way to the development of nappe 
structures in the "upper decken." 

Return to Route 9 and proceed east. 

7.10 Albite schist of the Hoosac Formation on the left. 



17 



Mileage (cont'd) 

7.60 Pass Shearer Hill Road on the right. 

7.95 Thick-bedded albite schist (similar to those rocks 

referred to by Hitchcock et al. , 1861, as the gneiss 
at Jacksonville) . 

8.4 5 Junction with road leading north to Lake Rayponda. 

9.40 Stop 3. HOQSAC FORMATION 

Park on the west side of the road at the picnic and 
rest area. Outcrops of fairly massive, slightly 
schistose, nearly vertical beds on the east side of 
the Molly Stark Trail. These vertically dipping beds 
strike N.55°E. and consist of garnet-biotite-muscovite- 
quartz-albite schist alternating with less micaceous, 
more gneissic beds and thin quartzites. The albite 
schist encloses buff-weathering calcite lenses and 
pods 1/4-2 in. 

This is one of only two localities in the Hoosac Forma- 
tion where carbonate lenses or beds have been observed 
in the Wilmington-Woodford area. If the Hoosac Formation 
proves to be a facies equivalent of the Readsboro albite 
schist, these carbonate pods may be the easternmost 
exposures of albite schists enclosing the Sherman Marble 
Meiriber of the Readsboro Formation. 

Continue east on Route 9. 

10.30 Stop 4. CHESTER AMPHIBOLITE 

Park on the roadside near Hogback Ski Area. Observe the 
dominantly easterly-dipping folded beds of the Chester 
Amphibolite near the Skyline Lodge and Restaurant. The 
Chester Amphibolite here is characteristically a well- 
laminated ankerite-bearing epidote-chlorite-hornblende 
schist with quartz lenses. Note overturned synformal 
fold plunging to the northeast in which the axial plane 
dips north. These beds and exposures of the intensely 
folded Chester Amphibolite and the Stowe Formation, 
well exposed for the next 3/4 mile on Route 9 east, are 
near the axis of the Hogback syncline. Figures 20-23 in 
Skehan (1961) are photos taken at Skyline and Hogback 
Mountain. On a clear day Shelburne Mountain and the 
Holyoke Range, Massachusetts may be seen from this stop 
along with Mount Monadnock and the White Mountains of 
New Hampshire. 



18 



Mileage (cont'd) 

Some may wish to walk east along Route 9 approximately 
1.1 miles to Stop 5. The drivers and those wishing to 
ride should proceed east on Route 9, a distance of 1.3 
miles . 

11.60 At the junction of the road to Adams School, Marlboro, 

turn right and park along the unpaved road leading south. 
Walk back along the highway 0.2 mile, and proceed westerly 
along a logging road to an ankeritic steatite deposit 
near the boundary of the Stowe and Moretown Formations 
(Fig. 1) . 

Return to cars. A trip to alternate Stop 5a can be made 
by continuing east on Route 9 as follows: 

4.75 Boudinaged amphibolite of the Stowe Formation on the 
north side of the highway. 

5.50 Stop 5a. VIEW STOP 

Just beyond the crest of a steep hill with large outcrops 
on either side of the highway, take a sharp right turn 
into the driveway of the Golden Eagle Motel. Park out 
of the way in the driveway. The view to the north 
looks toward Central Mountain on the boundary of 
the Wilmington and Brattleboro quadrangles, which is 
underlain by the rocks of the Missisquoi Formation (Fig. 1) . 
This view is shown in Skehan (1961, Fig. 26, p. 89). 
Proceed westerly on foot along Route 9 for 0.2 mile. The 
first outcrops on either side of the highway are thin- 
bedded amphibolites at the top of the Stowe Formation. 
More ample descriptions of the rocks of the Stowe 
Formation are given on pages 85-88 of Skehan (1961) . 
Mapping by Osberg (1965) has led to a number of correlations 
that indicate that the Stowe Formation is probably partially 
Cambrian and partially Ordovician in age. 

Within the Wilmington-Woodford area only two outcrops of 
unmetamorphosed basalt have been observed, one of which 
cuts the amphibolites of the Stowe Formation at this 
locality and may be observed on the south side of Route 9. 
The other is at Stop 3 of the Sunday Field trip of 
Skehan (this Guidebook). Outcrops of very coarse-grained, 
flattened and rotated garnets may be observed on the north 
side of the road on the Tannelli property. Please do not 
engage in unrestrained collecting of specimens of these 
rocks . 



19 



Mileage (cont'd) 

Return to cars and proceed west, returning to the 
intersection where cars were parked for Stop 5. Go 
south 0.55 mile on the road to Adams School at the 
crossroads. Continue south to Jenckes ' Farm. 

13.5 Stop 6 . PINNEY HOLLOW FORMATION 

Turn into Jenckes' Farm and park at the top of the 
driveway. Proceed south to the artificial pond and 
begin traverse downstream in the Green River. Excellent 
exposures of the Pinney Hollow Formation. A mode is 
presented in Skehan (1961, Table 21, p. 78) for a garnet- 
chlorite-biotite-muscovite-quartz schist from the 
Pinney Hollow Formation. Table 30 (p. 133) gives the 
chemical analysis of the chlorite from this formation. 
A traverse will be made downstream and up-section through 
the green schists and minor amphibolites of the Pinney 
Hollow Formation. The Pinney Hollow at this locality 
is typical of the Pinney Hollow of the east flank of the 
Green Mountains. For those making the Sunday Trip with 
Skehan (this Guidebook) note this rock and compare it 
with rocks to be seen at Sunday Stop 7. 

The Chester Amphibolite is well-exposed in the Green 
River and here is overlain by the thin sequence of black 
schists and quartzites of the Ottauquechee Formation and 
the garnetiferous chlorite-muscovite-quartz schists and 
minor amphibolites of the Stowe Formation. The Stowe 
Formation is lithologically indistinguishable in hand 
specimen or thin section from Pinney Hollow and from the 
green schists of the Cavendish, except that the latter are 
commonly more intensely deformed. In certain localities, 
the Pinney Hollow, the Stowe and the Cavendish carry 
chloritoid. 

Return to cars and continue south along road. 

14.60 Junction Green River Road, turn left (east). 

14.70 Junction with road to West Halifax, continue straight (east) 

14.90 Stop 7. MORETOWN MEMBER, MISSISQUOI FORMATION 

Park on the side of road. Outcrops in field to north of 
road are the Moretown Member of the Missisquoi Formation. 
Rocks are fairly typical, light gray quartz-mica schists 
with interlaminations of quartz-rich granulite and mica 
schist. The scale of the interlamination ranges from 
0.5 mm. to several centimeters. Porphyroblasts include 
garnet, chlorite, and biotite. 



20 



Mileage (cont'd) 

Return to cars, continue east on Green River Road. 

15.30 Entering Brattleboro quadrangle. 

15.60 Road junction in Harrisville, continue straight (east) 
on the Green River Road. 

16.00 Stop 8. BARNARD VOLCANIC MEMBER, MISSISQUOI FORMATION 

Park cars on the side of road. Small outcrops along the 
north side of the road are in the Barnard Volcanic 
Member. These outcrops show some of the variety of the 
rocks in the Barnard. Hornblende-plagioclase amphibolite, 
epidote amphibolite, and porphyritic amphibolite with 
prominent feldspar megacrysts are exposed here. Dark 
gray to brown weathering chloritic schists and light- 
colored felsic gneisses and schists are not as abundant 
here as they are elsewhere in the member. 

Continue east on Green River Road. 

16.20 Outcrops of Cram Hill Member, Missisquoi Formation. 

16.50 Stop 9. CRAM HILL MEMBER, MISSISQUOI FORMATION 

Park on the side of the road. This outcrop is typical 
of the Cram Hill Member, which consists largely of 
rusty-brown weathering, fine-grained, black phyllite 
and schist. The rusty weathering is due to finely 
disseminated pyrite and pyrrhotite. The only porphyro- 
blasts large enough to be seen here are biotite and 
pyrite. Bedding is difficult to distinguish where thin 
black quartzite interbeds are not present. A few amphi- 
bolites are present in the outcrop. A secondary cleavage 
cuts the schistosity here, causing the rock to break into 
elongated tabular blocks used locally as fence posts. 

17.50 Crossing Middle Ordovician-Silurian unconformity (not 
well-exposed along the road) . 

17.60 Outcrops of Northfield Formation. 

18.60 Stop 10. NORTHFIELD FORMATION 

Park with care along side of road. The Northfield 
Formation is a gray quartz-muscovite schist with con- 
spicuous garnet porphyroblasts 1 to 2 mm. in diameter. 
Biotite porphyroblasts are also common. The dip direction 
of the principal schistosity is changing in this area from 



21 



Mileage (cont'd) 

east-dipping off the Green Mountain anticlinorium to 
west-dipping adjacent to the Guilford dome to the east. 
A prominent slip-cleavage is present here and is probably 
related to the rise of the Guilford dome. The slip- 
cleavage is developed parallel to the axial surfaces of 
the minor folds of the third stage. The ubiquitous 
crinkles are the result of the intersection of the 
schistosity and slip-cleavage surfaces. 

19.50 Stop 11. WAITS RIVER FORMATION 

Park at the bottom of the hill and walk back uphill to 
outcrops on the north side of the road. These are 
fairly typical of the more calcareous portions of the 
Waits River Formation. The impure marbles weather a 
punky-brown with a friable surficial rind of the non- 
carbonate minerals left by the leaching of the carbonates. 
The fresh marble is steel gray. The modal percentages of 
carbonates in the impure marble beds range from 35 to 
70 percent. Quartz accounts for most of the rest of these 
beds with minor amounts of muscovite, biotite, garnet, 
plagioclase and actinolite present. Note the small 
"skarn" reaction zones at the contact of the marble beds 
and the surrounding mica schists. The large folds in 
the marble beds seen here are tentatively correlated 
with the second stage of minor folding, that congruous 
with the development of the Prospect Hill recumbent 
fold. 

Return to cars and continue east on Green River Road. 

19.60 Guilford-Halifax town line. 

20.20 Outcrops of Waits River Formation to north. 

20.70 Road junction, turn right (south) toward village of Green 
River . 

21.30 Stop 12. WAITS RIVER, STANDING POND, AND GILE MOUNTAIN 

FORMATIONS 

Park near abandoned farm house. Walk to north end of 
pasture. From here walk southwest across the pasture 
through the units in the Prospect Hill recumbent fold. 
The recumbent fold has been arched by the later doming 
so that now the units at this locality dip southwest 
away from the axial trace of the Guilford dome. The 
exposures in the pasture and along the base of the hill 
show a nearly continuous section through the Standing 



22 



Mileage (cont'd) 

Pond and Gile Mountain Formations. At the north end 

of the pasture, observe the contact of the Waits River 

Formation with the amphibolites of the Standing Pond. 

Note garnets to 1/2 inch but please do not remove 

them. Cross the Standing Pond amphibolites (small ridges) 

and interbedded brown weathering schists (small gullies) . 

On the second small ridge note the contact of the am- 

phibolite with a schist interbed. Which way is up? 

The Standing Pond here is some 400 feet thick. The Gile 

Mountain is exposed along the base of the hill and along 

the road (see as follows) . 

The Gile Mountain Formation consists of feldspathic and 
micaceous quartzites with thin mica schist interbeds . 
Kyanite and staurolite occur locally in these interbeds. 
The contact of the Gile Mountain with the Standing Pond 
at the southwest side of the pasture is placed at the 
appearance of the first amphibolite. A few thin beds of 
impure quartzite similar to those in the Gile Mountain 
occur in the Standing Pond here. Note the development of 
thin pink bands of coticule (spessartine garnet and 
quartz) in the Standing Pond near the contact with the 
Gile Mountain in the woods at the southwest end of the 
pasture. 

Return to road and to cars . 

Stop 12a. 

Walk south along road 0.1 mile to road cut in the 
typical interbedded feldspathic and micaceous quartzites 
and mica schists of the Gile Mountain Formation. The 
quartzite beds range from a few inches to 3 feet thick. 

END OF FIELD TRIP 

Return to cars, turn around, head north and proceed to 
Brattleboro and Burlington. 

22.00 Junction with road to Brattleboro, turn right (east). 

22.50 Outcrop of Waits River Formation dipping west off the 

Guilford dome. (Note hill to west — Governors Mountain — 
formed by the west-dipping Gile Mountain Formation and 
Standing Pond Volcanics in the Prospect Hill recumbent 
fold. Slopes on the west side of hill are essentially 
dip slopes.) 



23 



Mileage (cont'd) 

23.4 Outcrop of Waits River Formation. 

25.60 West-dipping Waits River Formation. 

27.10 Junction with unpaved road to left, bear right (stay on 
paved road) . 

28.60 Junction Route 9 in West Brattleboro. Turn right (east) 
and continue approximately 2.5 miles to junction 
Interstate 91. Take 91 north to 1-89 to Burlington. 
(Note — In the northbound entrance to 1-91 from Route 9 
there are excellent exposures that include the eastern 
band of the Standing Pond Volcanics. Here the Standing 
Pond is a quartz-plagioclase-hornblende-biotite granulite 
due to the lower, biotite zone, metamorphic grade.) 



2i^ 



BIBLIOGRAPHY 

Berry, W.B.N. , 1962, On the Magog, Quebec, graptolites: Amer . 
Journ. Sci. , v. 260, pp. 142-148. 

Billings, M.P., 1956, The geology of New Hampshire, Part II-- 
bedrock geology: N.H. Plan, and Devel. Comm. , 203 p. 

Cady, W.M. , 1956, Bedrock geology of the Montpelier quadrangle, 
Vermont: U.S. Geol. Survey Geol. Quad. Map GQ-79. 

Currier, L.W. and Jahns, R. , 1941, Ordovician stratigraphy of 
central Vermont: Geol. Soc. Amer. Bull., v. 52, pp. 
1487-1512. 

Doll, C.G., 1944, A preliminary report of the geology of the 

Strafford quadrangle, Vermont: Vt. Geol. Survey, State 
Geologist 24th Ann. Rpt., 1943-44, pp. 14-28. 

, Cady, W.M. , Thompson, J.B., Jr., and Billings, M.P., 1961, 

compilers and editors. Centennial geologic map of Vermont: 
Vt. Geol. Survey, Montpelier, Vermont, Scale 1:250,000. 

Emerson, B.K., 1898a, Geology of Old Hampshire County, Mass.: 
U.S. Geol. Survey, Mon . 29, 790 p. 

, 189 8b, Geology of the Hawley, Massachusetts-Vermont quadrangle; 

unpub. U.S. Geol. Survey, Folio 0. 

, 1917, Geology of Massachusetts and Rhode Island: U.S. 

Geol. Survey, Bull. 597, 289 p. 

Hatch, N.L. , Jr., 1967, Redefinition of the Hawley and Goshen 
Schists in western Massachusetts: U.S. Geol. Survey 
Bull. 1254-D, 16 p. 

, Osberg, P.H., and Norton, S.A., 1967, Stratigraphy and 

structure of the east limb of the Berkshire anticlinorium: 
pp. 7-16 in Field trips in the Connecticut Valley, 
Massachusetts, New England Intercollegiate Geological 
Conf . , 59th Ann. Meeting. 

, Schnabel, R.W. , and Norton, S.A., 1968, Stratigraphy and 

correlation of the rocks on the east limb of the Berkshire 
anticlinorium in western Massachusetts and north-central 
Connecticut, pp. 177-184 in Studies of Appalachian Geology — 
Northern and Maritime, Zen, E., White, W.S., Hadley, J.B., 
and Thompson, J.B., Jr., editors, Wiley Interscience , New 
York, 475 p. 



25 



Hepburn, J.C., 1972a, Structural and metamorphic chronology of 
the Brattleboro area, southeastern Vermont (abst) : 
pp. 20-21 in Geol. Soc. Amer . abstracts with programs, 
vol. 4, no. 1, January, 1972. 

, 1972b, Geology of the metamorphosed Paleozoic rocks in 

the Brattleboro area, Vermont: unpub. Ph.D. thesis, 
Harvard University, 377 p. 

Hitchcock, E et al., 1861, Report on the geology of Vermont: 
Vt. Geol. Surv., 2 vols., 982 p. 

Hubbard, G.D., 1924, Geology of a small tract in southern 
Vermont: Vt. Geol. Surv., State Geologist 24th Ann. 
Rpt., 1943-44, pp. 29-37. 

Osberg, P.H., 1965, Structural geology of the Knowlton-Richmond 
area, Quebec: Geol. Soc. Amer. Bull., v. 76, pp. 223-250. 

Perry, E.L., 1928, The geology of Bridgewater and Plymouth 
townships, Vermont: Vt. Geol. Surv., State Geologist 
16th Ann. Rpt., 1927-28, pp. 1-64. 

Prindle, L.M. , and Knopf, E.B., 1932, Geology of the Taconic 

quadrangle: Amer. Jour, Sci., 5th ser., v. 24, pp. 257-302. 

Pumpelly, R. , Wolff, J.E., and Dale, T.N., 1894, Geology of the 
Green Mountains in Massachusetts: U.S. Geol. Surv., Mon. 
23, 206 p. 

Richardson, C.H., 1933, The aerial and structural geology of 
Putney, Vermont: Vt. State Geologist, 18th Ann. Rpt., 
1931-32, pp. 349-357. 

, and Cabeen, C.K., 1923, The geology and petrography of 

Randolph, Vermont: Vt. State Geologist, 13th Ann. Rpt., 
1921-22, pp. 109-142. 

, and Maynard , J.E., 19 39, Geology of Vernon, Guilford and 

Halifax, Vermont: Vt. State Geologist, 21st Ann. Rpt., 
1937-38, pp. 349-57. 

Rosenfeld, J.R., 1954, Geology of the southern part of the 
Chester dome, Vermont: unpub. Ph.D. thesis. Harvard 
University, 303 p. 

Skenan, J.W., S.J., 1953, Geology of the Wilmington area, Vermont; 
unpub. Ph.D. thesis. Harvard University, 172 p. 

, 1961, The Green Mountain anticlinorium in the vicinity 

of Wilmington and Woodford, Vermont: Bull. 17, Vt. Geol. 
Surv. , 159 p. 



26 



Thompson, J.B., Jr., 1950, A gneiss dome in southeastern Vermont: 
unpub. Ph.D. thesis, Mass. Inst, of Technology, 160 p. 

, and Rosenfeld, J.R., 1951, Tectonics of a mantled gneiss 

dome in southern Vermont (abst) : Geol . Soc . Amer. Bull. 
V. 62, pp. 1484-1485. 

, Robinson, P., Clifford, T.N., and Trask, N.J., Jr., 1968, 

Nappes and gneiss domes in west-central New England, 
pp. 203-218 in Studies in Appalachian Geology — Northern and 
Maritime , Zen, E. , White, W.S., Hadley, J.B., and 
Thompson, J.B., Jr., editors , Wiley Interscience , New York, 
475 p. 



27 

Trip B-2 

MAJOR STRUCTURAL FEATURES OF THE TACONIC ALLOC HTHON 
IN THE HOOSICK FALLS AREA, NEW YORK-VERMONT 

by 

Donald B. Potter 
Hamilton College 

Purpose; We will see on this trip the two major thrust sheets that comprise the 
eastern part of the Taconic allochthon in this area. We will examine 
in detail some of the thrust contacts, and see the recumbently folded 
nature of the base of the lower thrust sheet. We will also see the 
Middle Ordovician submarine slide breccia, with its giant clasts, 
that occurs immediately beneath the allochthon. 

Background and acknowledgements This trip is based on a ten-year detailed 
stratigraphic and structural study (Potter, 1975) in the Hoosick Falls area 
(Figure 1). Field work has been supported by the New York State Geological 
Survey, the National Science Foundation, The Geological Society of America, 
and Hamilton College. Lane (1970) has made a detailed structural analysis at 
selected localities in the area aimed at deciphering the deformational history. 
His work is not intended to be an assessment of thrust-no thrust problem. 

E. Zen, W. Berry, J. Bird, G. Theokritoff, and D. Fisher have greatly 
aided Potter's study through field visits, identification of fossils, and through 
published data (see Zen, 1967 and references cited therein.) 

Prior to the present work the most definitive study in the Hoosick Falls 
area was by Prindle and Knopf (1932). Bonham (1950), Balk (1953), and 
Lochman (1956) have also contributed to our knowledge of the geology and 
paleontology of this area. MacFadyen (1956), and Hewitt (1961) mapped the 
quadrangles east and northeast, respectively, of the Hoosick Falls area; and 
Metz (1969) has recently mapped the Cambridge Quadrangle to the north. 

Stratigraphy While not the major concern of this trip, the stratigraphy of this 
area must be understood in at least summary fashion for the stratigraphic details 
enable us to establish structures which constitute prime evidence for the major 
thrusts. Figure 2 summarizes the relations of the two major stratigraphic 
sequences. 

The Taconic Sequence, comprising the allochthon, is approximately 4000 
feet thick, and consists of turbidites and pelites suggesting deposition in 
deep water with unstable bottom conditions: delicately laminated argillite 
and thin-bedded chert suggest deep, quiet water conditions; euxinic conditions 
are suggested by pyritiferous black slate with and without graptolities; 
transportation and deposition by turbidity currents is indicated by the litholigic 
character, graded bedding and sole markings of the major graywacke units; 
unstable bottom conditions and submarine slumping are indicated by 
intraformational breccias (ibc, Figure 2) and by the presence of a few exotic 
clasts in some of the units. Stratigraphic units within the Taconic Sequence 
show great continuity north and south within the allochthon, but exhibit 
maximum change in thickness and in lithic character east-west (across strike). 
Thus, practically every unit shown in Figure 2 can also be identified 60 miles 



28 



A 



H-*-ck 



a,,/.. 







dm.'^ 



(Sr^fl**^ 




ft f S 






ryPLANATlON 






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C««w^^'" •*•* 






0''Jo V*'*. /mm rwt/ii 



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P- P.tU/.,IJ 



A - R>uahk«mfijim P- PutUmJ 



FiQUrc /■ 



Oecfoy/c Setti'ta o-f He Tacomc H llochfhon ctncf 

fof.a'ton o/ tfic Hoo^K-k fal/'b A reel 




^ 
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31 





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6YNCLIN0RIUM ^CQUCNCE 



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/J Jar k fl'xv jktt vJ SJItip^ttt-k Breccia., Ja-i>> a-J <rlif p*f^f^ /J 
Aujf'i" O/f- <3rtifMat.ke Alack hlobi art ■Jt.k'Ktrime j)>Jt biacki 
ff iSjmcl'Oritm crhtn afft (**c)^ Tacin.c sS**aertee(i*T) nlcamaiui) 



n ' . r ' I ' .x 



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anj Jotoi't'onti (\5yac /■ » or, uim cmr bo />»tei) 



RP 



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nexsie Utr /"tatetu TArmjt fay It 



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<5 ^""\-^""^ 



\^cu)ftt>itjfitc/.mf, fraem af 'fcmmtamt jf* 

\x.l,Kt(rJ-i) bKt*atl> rteitm^af antn I.Mt Iratj 



Ml /eJ 



tiaurc O Geo/o^/C r/ap anJ u/ruc/ure Oecfion^ of Hoodie lalU area 



32 

north, at the north end of the allochthon. 

The Syncllnorium Sequence, largely synchronous with the laconic Sequence, 
is about 2000 feet thick and consists of limestones, dolostones, and quartzites 
that attest to a shallow water shelf environment. These are overlain by slate- 
graywacke-submarine slide breccia that mark the period of Middle Ordovician 
thrusting. 

Major structures and their evolution The allochthon in this area consists of 
two sheets, one above the other, that have been thrust westward onto the 
Synclinorium Sequence. Evidence for thrusting includes lithologic contrasts 
and gross structural discordance between synchronous formations above and 
below the thrust traces (Figure 3); slices of carbonate rock from the 
Synclinorium Sequence between the two thrust sheets (Stop 2); crushing, 
shearing, and mineralization at the thrust zones. The lower (North Petersburg) 
thrust sheet includes all the rocks of the Taconic Sequence except the 
Rensselaer Graywacke; recumbent folds are extensively developed in the lower 
1000 feet of this sheet which consists of younger formations than the upper part 
of the sheet (structure sections. Figure 3). The North Petersburg sheet is thus 
a huge recumbent anticline or nappe (Figure 4), and it is correlated with Zen's 
(1967) Giddings Brook slice (Figure 5). Beneath the North Petersburg thrust is 
the Middle Ordovician Walloomsac formation consisting of slate, graywacke, 
and submarine slide breccia. The Whipstock submarine slide breccia contains 
clasts of the Taconic Sequence and some giant blocks of carbonate rocks from 
the Synclinorium Sequence. It is inferred that thrusting was a submarine 
phenomenon, that Austin Glen Graywacke was deposited on both Taconic and 
Synclinorium sequences at the early stages of orogeny, that as the thrust sheets 
moved into this area from the east, blocks of limestone and dolostone up to 
1. 8 miles long and 700 feet thick (from the shelf environment) and blocks of 
Taconic Sequence rocks (from the advancing thrust sheets) slid westward into 
the mud in the deeper parts of the basin to form the Whipstock. Unconsolidated 
breccia, graywacke, and mud were overridden by the North Petersburg sheet, 
and, because of the gross overturning of this sheet, unconsolidated Austin Glen 
Graywacke of the Taconic Sequence was locally melded with the unconsolidated 
material beneath the thrust. 

The upper (Rensselaer Plateau) thrust sheet is perhaps the eastern core of 
the North Petersburg nappe which was thrust westward onto the core and 
inverted limb of the leading part of the nappe (Figure 4). On the plateau the 
Rensselaer Plateau sheet consists of Rensselaer graywacke and underlying 
Mettawee slate. Eight formations or stratigraphic units of the Taconic Sequence, 
ranging from Early Cambrian to Middle Ordovician, constitute the Rensselaer 
Plateau sheet on Mount Anthony and the Taconic Mountains. Identification of 
these units rules out MacFadyen's (1956) conclusion that the schists and 
related rocks here, which he called the "Mount Anthony Formation," are Middle 
to Upper (?) Ordovician and autochthonous. The correlation of this thrust 
sheet here with that capping the Rensselaer Plateau is based on the extensive 
exposures of Rensselaer Graywacke at the base of the sheet on Mount Anthony 
and on the Taconic Mountains (Figure 3), and on the fact that no other thrust 
sheet occurs between this one and the North Petersburg sheet or the autochthonous 
rocks below. Thus, Zen's (1967) Dorset Mountain slice in this area is considered 
to be the Rensselaer Plateau thrust sheet (Figure 5). 

Both major thrust planes and thrust sheets have been refolded by a later 
stage of deformation that produced a pervasive slaty cleavage-foliation. All 



33 




5 









o 



Si 



i 

« 

^ 






Hi 



uT 



3k 

the rocks in the area underwent a regional metamorphism in Middle Ordovician 
time. Increase in rank from west to east is shown by the recrystallization of 
limestones and dolostones, and by metamorphism of argillites and slates to 
phyllites and schists containing chlorite, chloritoid, sericite, and albite. 
High-angle reverse and normal faults, striking north- northea st , cut the two 
thrust sheets and the autochthonous rocks beneath. 

Lane's work suggests that four deformational episodes can be recognized 
in this area. The first, Dq, occurred at least in part before complete 
lithification of sediments, and consisted of large-scale westward transport 
and formation of recumbent folds and nappe structures. The next episode, D, , 
produced a system of NNE-trending , westward-overturned folds and a 
pervasive axial plane slaty cleavage, S,. Extensive mylonite zones along 
the Rensselaer Plateau thrust were formed contemporaneous with S^ , and 
metamorphism also occurred at this time. After the formation of S, and the 
mylonites. minor movement occurred on the Rensselaer Plateau thrust and 
perhaps on the North Petersburg thrust as well. D„ and D. established the 
overall geometry of structures in the central Taconics. Later deformations, in 
this area at least, served only to modify the structure. During D„ , the pervasive 
slaty cleavage was refolded on a NNE axis, and an axial plane slip cleavage, S 



was locally developed. The final episode of deformation, D- , caused folding 
of S, about an ESE axis, and locally developed axial plane slip cleavage, S„. 

The use of the term "deformational episode" is not intended to imply 
knowledge of temporally discrete deformations. It is possible that some of the 
deformations described may have been essentially continuous. 

STOP DESCRIPTIONS 

The location of each stop is plotted on the geologic map. Figure 3, and 
the general structural setting at each stop is indicated on the structure sections. 
The topographic maps (1:24,000) accompanying descriptions of Stops 1-6 show 
the limit of outcrops (fine dotted lines) and main geologic contacts. Refer to 
Figure 2 for letter symbols of stratigraphic units. 



2' 



35 






Ru tU^J 







"Zen's 0<?67) fArujt 

o^ mimp/m cm mfmt, oUmsT 
mf 6a t tarn) 



Gf ey lock j/ic»i 



S ne ft sj e /n e r PJai'eau jIicc 



^ C/iafham j/id 



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ZG, jJin^j 3r90k j/ice. 



T'Arust ^At€ts tft /i< 

Noe^ick f='m/h A fa. 
(fin r»p»rt) 



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MST£ 2»n's jl.<m * ,0 j'««A«- 
ft m*^^ m ALtH ^J^mt^miy ^im^t. 



Figure O. Lorre lai'j'on o-f Nor-fh Peiersi)ur^ cnJ Pe*tjje/mer P/afe*i 



'Crj 



36 



STOP-l 




North Pownal 
Quadrangle 



o 



Feet 



1 000 



Exposure of North Petersburg thrust fault, west of North Petersburg. 
Walk to thrust contact on steep slope (elevation 800 feet) via outcrops of 
limestone and dolostone of the Synclinorium carbonates. Steep slope above 
carbonates and below thrust is believed to be largely underlain by Walloomsac 
slate. There are a few small outcrops of slate on this slope, and a good 
exposure of the slate beneath the thrust fault 3/4 mile north of this stop. 
Less than five feet beneath the thrust fault, and inbedded in Walloomsac slate, 
is a large block of limestone (Synclinorium carbonate), interpreted to be a 
submarine slide block. 

The thrust zone is characterized by shearing, mylonitization, bleaching 
and calcification of argillites, cherty argillites, and slates belonging to the 
Owl Kill Member of the Poultney Formation. Above this, through a vertical 
distance of some 200 feet, is an inverted sequence of the White Creek Member 
of the Poultney (ribbon limestones in black slate). Hatch Hill (thin-bedded 
quartzites in dark gray slate). Eagle Bridge Quartzite, and Bomoseen Graywacke. 
The Bomoseen marks the core of recumbent anticline, ra-2 (Figure 3), one of 
several recumbencies in this part of the area that characterize the lower part 
of the North Petersburg nappe. 






37 



STOP-2 




North Pownal 
Quadrangle 



looo 

I ' . ■ ■ 1 

reef 



Exposure of the Rensselaer Plateau thrust fault north of Prosser Hollow. 
Below the thrust fault is an apparently normal sequence of Bomoseen, Mettawee, 
and Hatch Hill (with Eagle Bridge Quartzite) - all part of the North Petersburg 
thrust sheet. The Rensselaer Plateau thrust fault is marked by a large sliver of 
limestone and dolostone of the Synclinorium carbonates that have been 
tectonically dragged to their present position. Immediately above the 
Rensselaer Plateau thrust is the Rensselaer Graywacke, perhaps several 
hundreds of feet thick and intensely sheared. The graywacke is faulted against 
chloritoid schist (Mettawee) 0.3 miles east of this stop. 

The following details of the fault zone are noted. First, the Rensselaer 
Graywacke above the thrust is mylonitic through a zone approximately 150 feet 
thick (measured perpendicular to foliation), and the mylonitic foliation is 
concordant with normal foliation above and below the thrust zone (Figure 6). 
Second, the thrust plane truncates the mylonitic foliation. Third, a well- 
developed foliation parallel to the thrust plane occurs in the uppermost 2-3 feet 
of the limestone. Numerous other structural features may be observed. Widely 
spaced fractures parallel to the thrust plane also truncate the foliation and show 
a similar sense of movement to that on the thrust. Several warps in the thrust 
plane apparently represent areas where (later) movement on the thrust has 
locally followed the foliation instead of cutting across it. Near the upper 
(western) end of the outcrop, a sliver of mylonitic graywacke about 5' x 5' is 
completely enclosed within the limestone. West of this, the thrust plane 
steepens and follows the trend of the foliation in the graywacke for an indefinite 
distance. 



Two generations of folds are occasionally visible in the mylonites above 
the thrust. In one generation, the axial planes are parallel to the foliation; the 
axes generally trend to the north but are variable. In some cases, the plunge of 
the axes is perpendicular to the strike of the axial plane, thus forming a 
reclined fold. This fold style is common in other thrust zones, notably along the 
Moine thrust in the Scottish Highlands. The second visible generation of folds 
has NNE trending axes and nearly vertical axial planes. These folds are 
correlated with F„, one of the four fold systems in the non-mylonitic rocks in 



this area. 



2' 



38 

Interpretation: The earliest structural event well -represented at this 
stop is the formation of the pervasive axial plane foliation, S. , and the 
accompanying regional metamorphism. Emplacement of the graywacke and 
chloritoid schist along the Rensselaer Plateau Thrust may have occurred prior 
to the formation of S,. Evidence for this is the occurrence in several places 
along the thrust of tectonic slivers of autochthonous carbonates around which S, 
has been refracted. 

The mylonites either were pre S^ and rotated into their present orientation 
during the formation of S. , or else formed at the same time as the foliation. 

Following the ideas of Johnson (1967) the latter explanation is preferred. The 

mylonites are not necessarily related to large scale thrust movement, and 
consequently, evidence for emplacement of the Rensselaer Plateau thrust must 
come mainly from regional stratigraphic and structural studies. 

Following S. , minor movement occurred between the graywacke and the 
slates beneath. This movement caused the presently observed thrust plane, 

the thin zone of well-developed foliation in the upper few feet of the limestone, 
and the low angle fractures in the rocks immediately above and below the thrust. 
In other localities, notably west of the Little Hoosic Valley, and at Stop 3, the 
later movement caused a marked, but local, disturbance of foliation. 



Explanation of Figure 6. 

Equal area diagrams (lower hemisphere) showing orientation of poles to 
foliation in vicinity of Rensselaer Plateau thrust at Stops 2 (A-C) and 3 (D-F). 
Contours are 15%, 10% and 5% per 1% area unless otherwise indicated. 

A. Below thrust at STOP-2: 105 measurements. 

B. Thrust zone, within 5 feet of thrust plane, at STOP-2: 28 measurements. 

C. Above thrust at STOP-2: 42 measurements. 

D. Thrust zone, within 5 feet of thrust plane at STOP-3: 44 measurements. 

E. Above thrust, 20 to 50 feet vertically up slope to the NE of STOP-3: 
20 measurements. 

F. Regional trend of foliation in NE 4/9 of North Pownal Quadrangle. 
410 measurements. Contours are 10%, 5% per 1% area. 

These diagrams are intended only as a qualitative guide to foliation 
orientation. The contours are not statistically rigorous. 



39 



I 





r^yore 6 £faa/ area J.a^rams o/ poJc^ i-a -fo/^ai^on 



^0 



STOP- 3 




North Pownal 
Quadrangle 



O /OOO 

I .... I 



reef 



Exposure of folded Rensselaer Plateau thrust fault on west shoulder of 
Mount Anthony (this stop treats you to a 3/4 mile ride or walk, 700 feet relief- 
one way). The rocks beneath the thrust are autochthonous Synclinorium 
carbonates-limestones and dolostones. In the low ground north of the shoulder 
of Mount Anthony these carbonates are recumbently folded (axis of fold trends 
east-west) with Walloomsac slate. 

At closed contour 1300 we will see some least metamorphosed Rensselaer 
Graywacke. The thrust fault is exposed at elevation 1500. Immediately 
beneath the folded thrust plane the upper few feet of limestone is 
conspicuously thinly foliated, with foliation parallel to thrust plane. The 
graywacke above the thrust is schistose and contains characteristic seams of 
granular quartz. The foliation in the overlying graywacke is also parallel to 
the thrust plane, but within approximately 20-30' vertically, S, strikes NNE 
and dips moderately to steeply ESE, ie. , concordant with the regional 
attitude of foliation (Figure 6). The graywacke is mylonitic for several 
hundred feet up the slope. In thin section and occasionally in outcrop, a slip 
cleavage is seen to displace the mylonitic foliation. This cleavage is not 
related to any of the regional fold systems. 

As in Stop 2, the graywacke is believed to have been emplaced prior to 
the formation of the pervasive slaty cleavage and regional metamorphism. The 
mylonite formed at the same time as S, , and was locally deformed by later 
movement on the Rensselaer Plateau thrust. 



41 



STOP-4 




Hoosick Falls 
Quadrangle 

o /ooo 

Feet 



Exposure of Whipstock Breccia at Whipstock Hill. Several small 
scattered outcrops of Whipstock Breccia can be seen in the grassy terrain at the 
1180 crest of Whipstock JHill and these afford a close examination of the dark 
gray silty argillite or slate matrix, intraformational clasts, and a few exotic 
submarine slide blocks. 

The matrix of the breccia is irregularily cleaved because of the intra- 
formational clasts which range from about 1 mm. to 5 cm. in maximum dimension. 
Many of these small clasts lie in the plane of foliation and are smeared out and 
elongated so that they define a prominent lineation. The dominant clasts are fine 
grained serictic siltstone, green-gray argillite, quartzite, and fine grained 
limestone. The similarities between these lithologies and thin laminae and 
layers in the Walloomsac slate suggests an intrabasinal origin for the clasts. 
In addition, however, there are in the Whipstock exotic blocks of the Taconic 
Sequence, the Synclinorium carbonates, and volcanic rocks. Two exotic blocks 
can be seen at Whipstock hill: one is a conglomeratic quartzite (Rensselaer 
Graywacke or Zion Hill Quartzite), about 16 inches in maximum dimension, 
consisting of subrounded grains of quartz, quartzite, and oligoclase in a matrix 
of fine grained quartz, sericite, and chlorite. A second exotic block, about 
4x4 feet in plan, is inequigranular pyritic quartzite resembling the Mudd Pond 
Quartzite. 

The Whipstock Breccia on Whipstock Hill is infolded with a large mass of 
fine grained phyllitic siltstone, and recrystallized radiolarian chert (Owu), 
rocks of unknown stratigraphic position. These rocks may be beds in the breccia, 
large intraformational clasts, or perhaps giant clasts of the Taconic Sequence. 

The Whipstock is an integral part of the Walloomsac Formation. It is 
widely distributed beneath the North Petersburg thrust fault, and is closely 
associated with lenses of Austin Glen Graywacke. Its age is Wilderness or 
post-Wilderness for the breccia is underlain on the west slope of Whipstock 
Hill by a black slate containing graptolites of the Climacoqraptus bicornis Zone. 



1*2 



A similar submarine slide breccia (Forbes Hill) has been identified by 
Zen (1967) in the northern laconics; and wildflysch conglomerates are 
extensively exposed at the west edge of the allochthon (see Bird^ 1963, 
pp. 17-19). 

The crest and west flank of the Green Mountains are visible northeast of 
Whipstock Hill. Pre-Cambrian gneisses of the Mt. Holly Complex are exposed 
along the crest of the range, and the Lower Cambrian Cheshire Quartzite, which 
rests unconformably on the Mt. Holly, forms prominent dip slopes on the mountain 
flank. The Cheshire here is at the base of the Synclinorium Sequence. The 
Taconic Allochthon, being intermediate in facies between that of East Vermont 
(eugeosynclinal) and the Synclinorium Sequence (miogeosynclinal) presumably 
came from an area east of the exposures of the Cheshire Quartzite. Zen (1967) 
has proposed the Green Mountain core as the likely root zone. The prominent 
hill to the southeast is Mount Anthony, and the base of its steep north face 
marks the trace of the Rensselaer Plateau thrust fault. 



STOP- 5 




Hoosick Falls 
Quadrangle 



o 

L 



1000 



Feet 



I 



Exposure of large submarine slide block in bed of Little White Creek. 
The block here consists of Synclinorium carbonates and measures about 300 x 
400 feet in plan. Whipstock Breccia is exposed above and below the block 
which consists of highly folded limestone and dolostone (Old-l) overlain by 
black argillaceous limestone (Old-2). The contact between the black lime- 
stone of the block and the overlying Whipstock is locally conformable, but at 
the west (downstream) end of the exposure the contact between layers in the 
block and foliation in the breccia is discordant, and the Whipstock Breccia at 
the contact is crumpled, sheared, and faulted. Slaty cleavage in the Whipstock 
near the block is cut by a younger slip cleavage. 



The problem of identity of masses of Synclinorium carbonates as discrete 
submarine slide blocks ("ssb" on Figure 3) is difficult for exposures in the 
western part of the Hoosick Falls re-entrant are poor, and these carbonate 
masses could be isolated outcrops of the complexly folded carbonate sequence. 
The following evidence suggests a submarine slide block origin: 1. an 
apparent structural discordance occurs from one block to another in the area 
southwest of STOP 5; 2. discrete masses (blocks) of the Taconic Sequence 



^3 



occur in the same terrain; 3. limestones at five of the "blocks" carry 
fossils of Early and Middle Ordovician age, yet the blocks are surrounded by 
Mid. Ordovician breccia, graywacke, or slate, or occur at the contact 
between graywacke and slate. The last relation suggests that submarine 
sliding occurred after a thick accumulation of mud (Walloomsac slate) and at 
the onset of deposition of the Austin Glen Graywacke. 



STOP- 6 




Eagle Bridge and 
Hoosick Falls 
Quadrangles 

lOOQ 



Feet 



Recumbently folded Austin Glen Graywacke at readout on Route 22. 
The Austin Glen Graywacke, with interbedded dark gray slate and cross- 
bedded siltstones, is recumbently folded here in the core of recumbent 
syncline, rs-1, near the base of the North Petersburg thrust sheet. The 
exposure is apparently just east of the Case Brook reverse fault. Axial 
planes of recumbent folds here strike between N25° E and N80° E and dip 
from 13° to 23° southeast; axes plunge east-southeast from 3 to 20 degrees. 
Recumbent anticlines open to the northeast, synclines open to the southwest. 

The exposure is notable for its wealth of primary sedimentary structures 
which includes subtle graded bedding and sole markings in the graywacke beds, 
and various types of cross-bedding in the siltstones. 



I 



MILEAGE LOG 



Note : Depending on the size and interests of the group we may adhere strictly 
to the log or we may include unlogged localities to examine some of the 
stratigraphic and structural details within the laconic and Synclinorium 
sequences. 

Mileage 

00.0 Intersection of Routes 22 and J46 at North Petersburg. N.Y. This 

is the southern tip of the Hoosick Falls re-entrant. (See Figure 3) 
The valley bottom to the north and northeast is underlain by 
autochthonous carbonate rocks and slates of the Synclinorium 
Sequence. The North Petersburg Thrust Fault is exposed near the 
base of the steep hills to the west and northwest and above this 
thrust is the Taconic Sequence of formations. 

Turn north on Route 2 2 

00. 3 Park cars at transformer on west side of road and walk up steep 

slate-mantled slope, crossing a few outcrops of Synclinorium 
carbonates, to the North Petersburg thrust zone: STOP-1 

Return to cars and drive south on Route 22. 

00. 6 Intersection of Routes 346 and 22. Keep south on Route 22. 

01.3- Large exposures of recumbently folded Synclinorium carbonates on 

01.4 west side of highway. 

02. 1 Cross trace of North Petersburg thrust fault, and proceed south on 

Taconic Sequence formations near base of N. P. thrust sheet. 

02. 2 Barn on east side of highway, house on west. We are at north edge 

of younger (stippled) formations at core of Church Hollow anticline 
(Figure 3). Bold cliffs on Taconic Mountains to east are Rensselaer 
Graywacke near base of Rensselaer Plateau thrust sheet. 

02.8 Bomoseen Graywacke on west side of highway. 

03.0- Massive exposures of Mettawee slate (subfacies -b) on west side 

03. 5 of highway. These slates are at the core of the North Petersburg 

nappe. 

03. 5 Junction of Prosser Hollow Road and Route 22; turn east on Prosser 

Hollow Road. 

03.7 Cross Little Hoosic River 

04.4 White house on south side of highway, barn on north side. Unload 

for STOP-2 . Walk up (west) across field to spur for exposure of 
Rensselaer Plateau thrust fault. 

Return via Prosser Hollow Road and Route 22 to North Petersburg 



Mileaae 


08.2 


08.5 


08.8 



^5 



Intersection of Routes 22 and 34 6 at North Petersburg. Proceed 
east on 346. 

Cross Little Hoosic River. 

Turn north off 346 at intersection. Grassy low hills ahead underlain 
by Synclinorium carbonates; approximate trace of North Petersburg 
thrust fault marked by lower edge of woods. 

09.0 Cross B&M Railway and Hoosic River, bear left at intersection. 

09. 2 Cross 10-ton-limit bridge over B&M Railway. Immediately north of 

firidge are outcrops of Synclinorium carbonates. 

09.4 Walloomsac slate on right. 

10. 1 Turn right at road intersection and proceed around south end of Indian 

Hill (long finger of North Petersburg thrust sheet. Figure 3) on 
County Road 20. View to south (right) into Little Hoosic Valley with 
Rensselaer Plateau on west side of valley and Taconic Mountains on 
east. 

10. 7 Slates of the Owl Kill Member of the Poultney Formation on west side 

of road. 

11.5- Cross sheared and contorted sliver of Synclinorium carbonates which 

11.6 marks the hanging wall of Breese Hollow reverse fault. Walloomsac 

slate on foot wall to west. 

12. 1 Turn right (east) off County Road 20, and proceed to Cipperly farm. 

12.4 Unload at farmyard for STOP-3; Good exposure of metamorphosed 

Rensselaer Graywacke in R. P. thrust sheet, and of folded R. P. 
thrust plane. 

12. 7 Intersection of County Road 20 and Cipperly farm road. Proceed 

north on County Road 20. North nose of Mount Anthony visible to 
northeast. Rensselaer Plateau thrust fault is at base of upper steep 
slope. Green Mountains visible in background to north. 

Walloomsac slate on west side of road. 

Walloomsac slate on west side of road. 

Walloomsac slate and Whipstock Breccia on west side of road. 

14. 5 Red barn on right (north) side of road, Synclinorium carbonates in 

field on south side. 

14. 6 Intersection of County Road 20 and NY-7. Turn east on Route 7. 

15. 2 New York-Vermont line. Start Vt. -9. 



13.0 




13.4 




14.0 
14. 


1 



46 

Mileage 

'ft- 

16. 1 '-^rurn left (north) off Vt. -9 on Houran Road. 

16. 6 Unload at road bend for STOP-4; Whipstock Breccia on crest of 

''Whipstock Hill. 

17. 1 Intersection of Houran Road and Vt. -9. Turn right on 9. 
18.0 New York -Vermont line. 

19.4 Turn right (north) off N.Y. -7 on East Hoosick Road (County Road 51). 
Our route now takes us into the western part of the Hoosick Falls 
re-entrant. 

20.0 Walloomsac slate on left side of road. 

20. 5 Y intersection, bear left. 

21.2 Road from north intersects County Road 51. Keep straight. 
22. 5 Walloomsac slate on right side of road. 

22. 7 Walloomsac slate on right side of road. 

22. 8 Keep straight at intersection on County Road 124. County Road 51 

bears left. 

23. 1 View of west edge of Hoosic Falls re-entrant. The base of the hills 

to the west-across the valley of the Hoosick River-marks the 
approximate trace of the North Petersburg thrust fault. 

24.3 Intersection of County Road 124 and Rt. 22. Turn right (north) on 22. 
24.8 Cross bridge over Walloomsac River. 

25.0 Intersection of Rts. 22 and 67. Turn left on 22. 

25.05 Turn right off Rt. 22 on White Creek Road. 

25. 6 Unload for STOP-5 at private parking area near Little White Creek. 

USE NO PICKS AT THIS STOP. BE CAREFUL NOT TO DAMAGE DECKS 
OR WALKWAYS. FOLLOW THE LEADER. We will see a large 
submarine slide block of Synclinorium carbonates surrounded by 
Whipstock Breccia and Walloomsac slate. 

25. 65 Continue north on White Creek road. Cross bridge over Little White 

Creek. Whipstock Breccia in stream bed upstream from bridge 
(right side of road). Some clasts (not the cobbles in old concrete 
dam) in breccia are 6 to 8 inches in diameter. 

26. 1 Y intersection. Bear left on dirt road, then straight ahead at 

intersection 150 feet north. 

27.4 Turn left (west) at intersection on County Road 63. Recumbently 
folded formations at base of North Petersburg nappe exposed on 
steep wooded hill to north. 



47 



Mileage 



27.9 County Road 63 intersects road leading south to Eagle Bridge. 

Keep straight on 63. Grassy hill in foreground to south is under- 
lain by fossiliferous West Castleton, at the base of the North 
Petersburg nappe. Low grassy land south of hill underlain by 
Austin Glen Graywacke Member of the Walloomsac In middle 
distance to south is the North Hoosick klippe with trace of North 
Petersburg thrust fault at lower edge of woods, Austin Glen 
beneath the thrust, and allochthonous Lower Cambrian formations 
above. 

28.2 Intersection of County Road 63 and Delevan Road. Grassy hill on 
right (north) capped by fossiliferous West Castleton limestone, 
and dolo stone. 

29. Intersection of Lincoln Hill road with County Road 63 at Post 

Corners. 

29.3 Recumbent anticline (ra-1. Figure 3) in low ground to right (north), 
nested below other recumbent folds which are well exposed on 
slopes of hills in background. 

29.5 Hatch Hill black slate with interbedded calcareous quartzites on 

right side of road. 

30. 2 Intersection of County Road 63 and Rt. 22. Turn right (north) on 22. 

30. 5 Slate of the Owl Kill Member of Poultney Formation exposed on east 

side of highway. 

30. 6 Unload for STOP-6 . BEWARE OF TRAFFIC. We will see here 

recumbently folded Austin Glen Graywacke Member of the Normanskill, 
near the base of the North Petersburg thrust sheet. Gross structures 
best seen from west side of highway. 

END FIELD TRIP 

Burlington is about 110 miles to the north. Best route is 22 to Middle 
Granville, 22A from M.G. to Vergennes, and 7 from V. to Burlington. 



48 

REFERENCES 



Balk, Robert, 1953, Structure of the graywacke areas and laconic Range, east of 
Troy, New York: Geol. Soc America Bull., v. 64, pp. 811-864. 

Bonham, L. D. , 1950, Structural Geology of the Hoosick Falls area, New York - 
Vermont in relation to the theory of laconic overthrust: University of 
Chicago PhD Thesis, 111 p. 

Hewitt, P.C. , 1961, The geology of the Equinox quadrangle and vicinity, 
Vermont: Vermont Geol. Survey Bull. 18, 83 p. 

Lochman, Christina, 1956, Stratigraphy, paleontology, and paleogeography of the 
Elliptocephala asaphoides strata in Cambridge and Hoosick quadrangles. 
New York: Geol. Soc America Bull. , v. 67, pp. 1331-1396. 

Johnson, M.R.W. , 1967, Mylonite zones and mylonite banding. Nature, v. 213, 
pp. 246-247. 

Lane, M.A. , 1970, Structural Geology and Structural Analysis of part of the 

Central Taconic Region, Eastern New York, U. of Indiana PhD Thesis, 68 p. 

MacFadyen, J. A. , Jr. , 1956, The Geology of the Bennington area, Vermont: 
Vermont Geol. Survey Bull. 7, 72 p. 

Metz, Robert, 1969, Taconic Stratigraphy of the Cambridge Quadrangle, New York: 
(Abs.): Program for 1969 Ann. Mtg. , Northeastern Section Geol. Soc. 
America, Albany, N.Y. , p. 41. 

Potter, D. B. , 1972, "Stratigraphy and structure of the Hoosick Falls area, east- 
central Taconics, N.Y. -Vt. ", N.Y. State Museum and Science Service 
Map and Chart Series No. 19. 

Prindle, L. M. and Knopf, E.B. , 1932, Geology of the Taconic quadrangle: 
Am. Jour. Sci. 5th ser. , v. 20, pp. 257-302. 

Zen, E. , 1967, Time and Space Relationships of the Taconic Allochthon and 
Autochthon, Geol. Soc. America Spec. Paper 91, 107 p. 



49 



Trip B-3 

EXCURSIONS AT THE NORTH END OF THE TACONIC ALLOCHTHON AND THE 
MIDDLEBURY SYNCLINORIUM, WEST-CENTRAL VERMONT, WITH EMPHASIS ON 
THE STRUCTURE OF THE SUDBURY NAPPE AND ASSOCIATED PARAUTOCHTHONOUS 

ELEMENTS 

by 

Barry Voight, Department of Geosciences 

The Pennsylvania State University 

University Park, Pa., 16802 



SUfdf-lARY 

This excursion is designed to provide insight into the 
Paleozoic displacement and strain patterns at the juncture of the 
Taconic Allochthon and .'liddlebury Synclinorium. The nature of 
structural contacts will be examined in detail, and sequences of 
fault, fold, foliation and lineation evolution will be examined. 
Field trip stops will include locations within the allochthon and 
tne synclinorium in order to place their mutual boundary relation- 
ships into proper perspective. 

Assembly point: front of the office of the Vermont Struc- 
tural Slate Company, near junction Routes 4 and 22A south of Poult- 
ncy River in Fair Haven, Vermont. 8:30 A.M. sharo, Saturday, Oct- 
ober 14. 

Quadrangle maps: Sudbury (1946) , Bomoseen ( 1944) , Thorn 
Hill(1946), and Middlebury (1963) 7 1/2' topographic sheets. Most 
stops will be in the Sudbury quadrangle. 

The two standard published references for the area of the 
excursions are: 

Cady, W. M. , 1945, Stratigraphy and structure of 
west-central Vermont: Geol. Soc. America Bull., v. 46, p. 515-558. 

Zen, E-an, 1961, Stratigraphy and structure at the 
north end of the Taconic Range in west-central Vermont: Geol. Soc. 
America Bull., v. 72, p. 293-338. 

Excursion participants may wish to review these references in ad- 
vance of the field conference. Also to be recommended is the more 
recent review of Taconic geology by Zen (1967) . 

Begin Excursion: Enter Fair Haven Village and turn west 
on Route Tl Stop, approximately 2.5 miles at William Miller Chapel 
south of Route 4 . 

Locality 1 : T aconic thrus t ; Structural Window at William 
Miller Chapel - An area of intensely-deformed Ordovician Beldens 



50 



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52 



limestone and dolostone (Chipman formation, Cady and Zen, 1960) 
overlain in nearly horizontal contact by the early Cambrian Bomo- 
seen graywacke member of the Bull formation (Figure 1; cf. Zen, 
1961, Figure 4, p. 1.3; Plate 1). This is a structural window 
(Figures 1,3) in which the autochthonous carbonate is exposed 
through an overthrust fault sequence. The superjacent allochtho- 
nous sequence within the general vicinity is normal, showing that 
at least here no recumbent fold (Figure 2, B-B') exists in the 
Taconic sequence (Zen, 1961, p. 319; Plate 1). The structural con- 
tacts are locally exposed and can be examined in detail; there is 
no outcrop to the South. 

The Bomoseen graywacke (Zen, 1961, p. 301-302) is typical- 
ly a hard, olive-grey, coarsely-cleaved rock, weathering to white 
or to pale brick red. Quartz and feldspar grains, typically 1 mm, 
are common; white mica occurs in alignment with cleavage surfaces. 
A common assemblage is muscovite-chlorite-albite-microcline-stil- 
pnomelane-quartz. Zen has presented evidence suggesting that the 
Bomoseen graywacke is a lithofacies that becomes progressively 
older and thicker to the west. It is the oldest unit in the Tac- 
onic sequence exposed west of Glen Lake. 

The Beldens member of the Chipman formation is typically 
a white marble limestone with local interbeds of orange- to buff- 
weathered dolostone. 

Return to Fair Haven and take the Scotch Hill road north 
to West Castleton. 



Interlude ; The first quarrying of slate in Rutland County was done 
by Col. Alanson Allen of Fair Haven in 1839 on Scotch Hill, about a 
mile north of Fair Haven village. The first quarry was worked for 
8 years, using the products for hearths, headstones for cemeteries, 
school slates and flagging for walks, before any roofing slate was 
manufactured. It was one year more, in 1848, before the first roof 
was covered with Vermont slate. This was done by Col. Allen under 
the following conditions. He was to wait for one year for his pay, 
and if, in the meantime the roof should break down from the weight 
of the slate, he was to receive no pay, but should pay all damages. 
The farmer was disappointed and the roof is good today (Smith and 
Rann's, History of Rutland County, 1866). The barn still stands 
on the farm of Stanley Kruml , about a mile south of Fair Haven on 
Rt. 22-A; the roof is in excellent condition. 

Locality 2 : Scotch Hill Syncline, West Castleton - This 
is private property. We are permitted to be here by the courtesy 
of the owners. Sampling of rock specimens is not permitted; LEAVE 
ALL HAT^I^ERS IN THE VEHICLES ! Please cooperate — thank you. 



53 




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Exposed cross-section of the Scotch Hill syncline : the 
east limb is nearly vertical at this locality (Figure 4). The 
west limb dips east at a shallow angle. This is the West Castle- 
ton formation (Zen, 1961, p. 304), within which early Cambrian fos- 
sils have been found by several workers, in ledges near this local- 
ity. 

The West Castleton formation ranges from a dark-grey, hard, 
poorly-cleaved sandy or cherty slate that weathers white or pale-red 
to a jet-black, fissile, graphitic and pyritic slate that contains 
many paper-thin white sandy laminae and commonly also black cherty 
nodules, and when weathered displays much alum bloom. Locally in- 
terbedded in the fine black slate are beds of buff-to yellow-weath- 
ering black dolostone or dolomitic quartzite, a few inches thick, 
some of which, however, become massive, siliceous, and heavily bed- 
ded in the harder black slate. The varieties of black slate do not 
form mappable units but grade into each other along strike (Zen, 
1961, p. 304-305). The rock becomes a phyllite to the east. 

Immediately to both the east and west of this fold are 
quarry belts of green and purple slates (Mettawee member. Bull for- 
mation) . The simplicity of the Scotch Hill structure and the rela- 
tion to the underlying Bull formation is consistent with the rela- 
tive ages of the two units as proposed by Zen (1961, p. 317). The 
flexural flow fold displays a host of well developed minor struc- 
tural elements, e.g. cleavage in several rock types, "refraction" 
of cleavage, slip and flow phenomena in the dolostones; calcite- 
filled fractures; and pressure-shadows associated with porphyro- 
blasts. Cleavage is axially-planar in thicker slate beds. 

The dating of the cleavage is an important but unclosed 
question; Zen (1967, Appendix 7, p. 101) has suggested a post-Ordo- 
vician age of the regional metamorphism based both on regional re- 
lations and on radiometric dating. Zen noted that the regional 
metamorphic grade increases steadily eastward, from the non-meta- 
morphosed rocks of the Chcimplain Valley, to almandine-kyanite 
grades in eastern Vermont. No multiple-metamorphic effects were 
observed in the Paleozoic sequence; rocks as young as Devonian are 
involved and the metamorphic episode was presumed to postdate this. 
Radiometric dates in the range 350-390 m.g., from the southern Ta- 
conic region and from north-central Vermont (Camels Hump area) are 
cited by Zen in support of this view. Yet Harper (1968) has cited 
radiometric dates from slate belt minerals in the range 445-460 
m.g. , which dates would be compatible with Ordovician (Taconic) de- 
formation. This problem remains unresolved, and demands attention; 
a correct interpretation of regional structural relationships with- 
in the "Taconic" and "synclinorium" areas hinge upon its resolution. 

Drive eastward along the Cedar Mountain Road to the (dead) 
end. Quarry on the left at the end. 



55 



k 



Locality 3 : Cedar Mountain Syncline; slate quarry 
This, the first major structure west of Lake Bomoseen, is specta- 
cularly exposed in the abandoned quarry cut into Cedar Mountain 
(Figure 4). Fold is overturned to the west, nearly recumbent, 
and plunges south; axial plane cleavage dips gently eastward. The 
deformational mechanism associated with the exposed portion of the 
fold, appears to be (chiefly) passive flow; on a larger scale, 
flexural mechanisms may have played a role. Exposed rocks are in 
the upper beds of the Bull formation , Me ttawee slate facies (Zen, 
1961, p. 300-301), chiefly a soft purple" and green slate with loc- 
al thin beds of limestone. 

Typical mineral assemblages are muscovite-chlorite-albite- 
quartz and muscovite-chlori te-hematite-quartz (Zen, 1961). 

The anticline separating location 2 and 3 is not well ex- 
posed here, being for the most part masked in the pervasive cleav- 
age of the Mettawee slates; its presence, however, is indicated by 
exposures of Bomoseen graywacke southwest of Lake Bomoseen (Zen, 
1961, Plate 1) . 

The purple and green colors of these slates reflect dif- 
ferent relative proportions of chlorite and hematite. Certain col- 
or features bear on the question of whether or not chemical equi- 
librium was obtained during conditions of metamorohism (Zen, 1960, 
p. 167) : thus it may be observed that hematite-bearing purple 
slates are never found in contact with graphite-bearing black 
slates without an intervening layer of green slate and that pyrite- 
spots and limestone layers in purple slates are always surrounded 
by a rim of green slate. These layers are reaction rims; this ev- 
idence, together with textural data and the observation that min- 
eral assemblages obey the phase rule, suggest the rocks have, in 
the main, achieved chemical equilibrium during metamorphism (Zen, 
1960) . 

Within the cleavage plane a subtle lineation can sometimes 
be observed; this is termed "grain" by quarrymen. Grain has been 
observed to be roughly perpendicular to fold hinge lines; it ap- 
pears to be formed from a preferred orientation of elongate mineral 
grains, although definitive evidence on microstructure of the fea- 
ture has not been reported. As a working hypothesis, the writer 
has believed "grain" to be the direction of greatest finite exten- 
sion within the plane of flattening; this view remains hypothetical. 
Nonetheless the feature may ultimately prove to be an important one 
in structural analysis. In support of this view, Wright (1970, p. 
55) observed ellipsoidal green reduction spots in purple slates, 
and concluded that the longest dimension was parallel to the grain 
direction. Reduction spots appear to be reliable as strain indica- 
tors, and the implication is that "grain" may also be a useful 
strain indicator. The reduction spots have long and medium dimen- 
sions within the plane of flow cleavage; flow cleavage is thus pre- 
sumed to have developed perpendicular to the axis of greatest finite 



J 



5(> 




57 



compressional strain. It should be noted that this direction is 
in general not equivalent to the axis of maximum compressional 
stress. Maximum values of analyses of flattening in the Vermont 
slate belt, based on reduction spots, is approximately 80% (Wright, 
1970, p. 64) . 

Larrabee (1939-40) and Dale (1899) have discussed the 
principles of structural geology in relation to flagstone and slate 
quarrying. Within the slate belt of Vermont and adjacent portions 
of New York State, slate and flagstone are quarried from three rock 
units; the Mettawee Slate, the Poultney Slate, and the Indian Riv- 
er formation. Mettawee yields purple, grey, and rarely grey 
slates; Poultney slates are grey-green, and the Indian River red 
and blue-green slates. The latter is quarried only in New York, 
near Granville. 

Interlude : To the south of the quarry is Neshobe Island, formed 
principally of slates of the West Castleton formation, but locally 
containing the Beebe limestone member of the West Castleton forma- 
tion, a massive, lenticular black limestone. A thin band of Met- 
tawee slate occurs at the eastern extremity of the island. Of 
greater interest perhaps is the observation that author Alexander 
Woolcott owned the island in former years, and that such diverse 
fauna as Marx Brothers were known to have prowled through its lush 
undergrowth. 

Due east, on the crest of the Taconic Range, is the 1976-foot peak 
of Grandpa Knob. Here, in 1941-45, Palmer Putnam's 1500-kilowatt 
wind turbine made electrical research history. A 150-foot wind- 
mill with stainless steel blades generated power that was fed into 
utility lines of the Central Vermont Public Service Corporation, 
Rutland. A technical success, financial obstacles hindered further 
development when, in 1945, one of the eight-ton blades had been 
ripped from its shaft and tossed 750 feet down the mountain. 

Return to West Castleton; turn north on Moscow-Black Pond- 
Hortonville Road to its intersection with the Seth Warner Memorial 
Highway (Route 30) . A few miles to the southeast of the road in- 
tersection is the site of the Battle of Hubbardton , the only con- 
test fought on Vermont soil during the American Revolution, on Ju- 
ly 7, 1777. A museum at the site is contained within an 18th cen- 
tury-style building; it features an animated electrical relief map 
and diorama depicting the important stages of the battle. (The Bat- 
tle of Bennington took place on New York soil) . Turn north along 
Route 30, for about 0.5 miles. Stop south of Eagle Rock camp 
(parking may be difficult) . 

Locality 4 : Structure of the Giddings Brook "Slice" : 
Problem of the Giddings Brook -Ganson Hill Fold Complex - In the 



58 




Figure 5, Schematic diagram showing the geometry of the 
Giddings Brook bottoming fold as proposed by 
Zen (1959» PI. A-4j I96I, Fig. 4). Surface 
shown is the top of the Biddle Knob formation. 
Topographic effects are ignored. The structure 
is shown to be recumbent with a shallow South- 
plunging hinge line. 



59 




Figure 6. Schematic diagram showing the geometry of the 
hypothetical Giddings Brook bottoming fold 
with the outcrop pattern of West Castleton 
formation and younger rocks included in plan 
vif»w, and its inferred profile. 



60 



east-central part of the geologic map (Figure 1) there is a large, 
boomerang-shaped tract of Biddie Knob formation, and a half -moon 
shaped area of the West Castleton formation and the Poultney Riv- 
er group immediately to the northwest (Zen, 1959, p. 3); these 
represent the Giddings Brook-Ganson Hill fold system of Zen (1961, 
p. 316) , in which the Biddie Knob formation is assumed to form the 
core of recumbent "bottoming fold"* along the Giddings Brook val- 
ley, and the West Castleton and younger rocks are assumed to be 
contained within a recumbent syncline, the Ganson Hill syncline 
(also a "topping" fold) . Locality 4 in Figure 1 occupies the west- 
ern tip of the Ganson Hill syncline. The schematic diagram shown 
in Figure 5 (cf.. Figure 2, A-A' ) provides a clear picture of the 
structural geometry as envisaged by Zen (1959, Plate A-4; 1961, 
Figure 4) . 

Such a structure seems plausible if only the Biddie Knob 
formation is considered; but in my view it seems implausible when, 
in addition, West-Castleton and younger rocks in the vicinity of 
Ganson Hill are considered. The Ganson Hill syncline exhibits clo- 
sure at its western end near the Seth Warner Memorial Highway, as 
previously shown by Zen (1961, Plate 1; p. 316) and other workers. 
This would require a schematic illustration something akin to Fig- 
ure 6, which in turn suggests the "cylindrical" structure portray- 
ed in Figure 7. Such a structure would be explicable only by 
large-scale boudinage; this latter hypothesis does not appear to 
fit the field evidence, which evidence suggests that the Ganson 
Hill structure is a comparatively shallow overturned syncline with 
a flat northeastrtrending hinge line, comparable to and possibly an 
extension of the Scotch Hill syncline (Locality 2). 

Continue north on Route 30 to Sudbury. 

Interlude : Church at Sudbury Village. Built in 1807 and later 
granted joint use by town and the congregational services, the ex- 
terior shows in its design the lingering tradition of "gothic" de- 
tail of Old England's churches. The former galleries have now 
been replaced by a floor, the Town Hall being on the ground floor 
and the religion services upstairs. 

Take the road southeast from Sudbury Church for 0.6 mile 
to sharp turn with road cut. Go through fields westward to expo- 
sures of white marble, crossing a "Taconic thrust"; follow the con- 
tact southward . 

*Zen (1961 , p. 313-314) introduced two new terms in order to des- 
cribe the structural complexity of this area: "By topping fold is 
meant a fold whose core contains the relatively youngest beds . 
By bottoming fold is meant one whose core contains the relatively 
oldest beds. For rocks that have only been simply folded, these 
terms are equivalent to synclines and anticlines, respectively; 
however, for rocks which have been complexly deformed, these terms 
are not necessarily synonyms ... topping- and bottoming folds are 
terms with stratigraphic connotations." 



61 



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62 



Locality 5 ; Taconic Margin east of Hyde Manor and Sud- 
bury; Historical Ground for Taconic Controversy - Here Taconic 
sequence rocks of the "Signal Hill Slice" (viz., all Taconic se- 
quence units north of the Keeler Pond fault of Zen (1961, Plate 
1; cf. Voight, 19.65) overlie parautoch^onous rocKs of the Sud- 
bury nappe in imbricate thrust contact (Figures 8, 9, 10; cf. Kay, 
1959). The field relationships here suggest that Arthur Keith's 
original evidence for the Taconic klippe, which had long since 
fallen into disrepute, was basically correct. Keith (1913) main- 
tained that an overthrust was indicated because the limestones 
and slates were unconformable with the general contact: "Inasmuch 
as the divisions of the Ordovician Stockbridge limestone in this 
area dip under the slates known to be Cambrian and these in turn 
dip and pitch away from the limestone, and inasmuch as the lime- 
stones and slates are all unconformable with the general contact, 
an overthrust seems the only competent explanation." Keith was 
correct; the fact that Keith probably misidentif ied the infolded 
black Hortonville slate, and the possibility that local occurrenc- 
es of so-called "Taconic sequence" slates may also be Hortonville, 
have little bearing on this general conclusion. This is a thrust 
contact, not simply an unconformity as had been contended by some 
subsequent workers. 

Also of historical interest is an "outlier" described by 
T. N. Dale, one of the pioneers of Taconic geology. In his 1904 
paper describing the geology of the northern Taconic region. Dale 
cited an "outlier" west of Hyde Manor as evidence that the carbon- 
ate sequences lay unconformably on top of the slate-phyllite Tac- 
onic sequence rocks. Subsequently Ruedemann (1909), in the first 
suggestion that a "Taconic thrust sheet" underlay the slate belts, 
cited Dale's "outlier" as a true "fenster" and called it "positive 
evidence" for the overthrust. Ruedemann claimed that the limestone 
was an anticline protruding from below, rather than a syncline as 
visualized by Dale. The Ordovician age of the "outlier" limestone 
was known from fossil evidence (streptelasma, crinolds) as reported 
by Dale. Valuable as is the use of imagination in geplpgical in- 
r vestigations, geological sciences are a till 1 best advanced by care- 
ful observation and deduction; thus heeiplihg his own wpr^s , Dale 
advanced in 1910 on the outcrop and, 'JwIl^ the aid 0f fWo men and 
-dyneunite" made six excavations^ in 19||l|Djale drilled a jsore through 
tthe center of ; the outcrop. that'pjanetrS^ti^d the c»i:l>pn;ij^^ layer at a 
'depth of 14 feet (Figures il, 12). Rui^demann's ;fefttt^^i theory was 
tlius deemed uAlikely (Dale, 1912) r but not lnvalid«i«ijliisonpletely , 
for an overturned 'anticline with an east-dipping jilclal "plane could 
be cpmpatible with dr-ill c6re data. Hence Dale :3[19|3j. continued 
his ^tudy of the\^locality,'^ increasing the number^ of ^^cavations to 
fifteen, and drilled another core, inclined 45*,?rouc^^ parallel 
to the axial plane, which passed through limestone artg^^out 32 feet 
(Figujre 11) . These papers by Dale might well be consl&red classic 
but in fact do not seem to be well known. ^ cVD'u w 

pushing and Ruedemann (1914, p. 113) then admitted the like- 
lihood of (the outcrop as representing a small infolded mass , but at- 

1..' 



63 




sedimentary contact 
\^^\ thrust troce 
Y^\ high angle fault 
I ° I road intersection 



Fi-urv- 8, Geology of Sudbury nappe region. 



64 



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EXPLANATION 

LITHIC UNITS 

ALLOCHTHONOUS SEQUENCE 

Block slole, oqe uncetloin I •'■'•'' I 

Vitreous quotlzile, oge unceflom I "a*" I 

Ferruginous quortzile L*£^ 

PARAUTOCHTHONOUS SEQUENCE 

Hoilonnille Fm .block stole l'''l 

Middlebuiy, Oriell, Glens FbllsPI . limestone I '^- I 

Beldens Member, Chipmon Fm 'dolomite l°°° I 

Beldens IMember, Chipmon Fm tcolcite morble I I 

STRUCTURAL SYMBOLS 

Sedimentory conloct . ticks on structurolly-upper loyer I ^-^i 

Bedding Surloce I -^ I 

Horizontol Bedding I ^ I 

PHASE I STRUCTURE 

Secondoiy Foliolion (S;). slote I -^ I 

Secondory Foliotion (Sj) ' corbonotes ' -^ I 

S; ond Penetrotive Lineolion . slote I -^ I 

Sj and Penetrotive Lineolion ;corbonotes I -^ I 

Thrust Foull Troce . corol on upper plote l-^^l 

Boudinoge, dolostone in morble l^i^lU 

Fold Hinge Line . I "^ I 

PHASE II STRUCTURE 

Secondory Foliolion (Sj) I -^ I 

Verticol (Sj) _ . _ I -^ I 

Fold Hinge Line _ I '^ I 

TOPOGRAPHIC SYMBOLS 

Building or Remnant Foundotion_ . . I ° * I 

Fence _ I' ■ I 

Contour Line I »°° I 

Swomp ... . . I -*" I 

Intermittont Streom _ . . L ~ 1 



GEOLOGIC MAP 
of the 

TACONIC MARGIN 

between latitudes of 
HYDE MANOR and SUDBURY, VERMONT 



././. V 



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(ieology hy Barry ioight 
i artoftraphy by R.J. Texter 



Firure 9, Geologic map of the Taconic Marf^in between latitudes 

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tempted to diminish its importance because of its small size. 
Kaiser (1945, p. 1095) commented that Dale's investigations were 
of historical value only, since present workers "agree that the 
slate is on top of the limestone here"; he discounted the drill 
core evidence. Keith was at the outcrop with Dale when field work 
for Dale's 1912 paper was in progress, but never mentioned it in 
his brief accounts of the geology of the region (1912, 1913, 1932, 
1933) although he must have considered it in evidence. Most other 
workers have not cited it. Notwithstanding the above, a multiple 
working-hypothesis approach is effective only if a sufficient num- 
ber of hypotheses are included in those to be tested. In this in- 
stance the "outlier" seems to be but one of several located near 
the "Taconic" margin; more recently they have been interpreted, 
not as "outliers" or "fensters", but as carbonate slivers caught 
up in imbricate thrust slices (Voight, 1965) . The "outlier" of 
Dale is the most southerly of the tectonic "lenses" shown in Fig- 
ure 9. Similar imbricate relationships have been observed at the 
northern tip of the "Taconic" margin (cf. Figures 8, 13, 14). 

Interlude : The FIFTH, who chanced to touch the ear, 

Said: "E'en the 'blindest man 
Can tell what this resembles most; 

Deny the fact who can. 
This marvel of an Elephant 

Is very like a fan ! 

Return to Route 30 via Sudbury; turn north on Route 30 
approximately two miles to the Webster School, and turn left toward 
Orwell. Stop about 2.3 miles to the west, before the Lemon Fair 
River Bridge. Cross fence (keep all gates closed !) and enter 
fields to the north of the road. 

Interlude : Any wandering movement would have to occur across the 
mountain chain... The "axles" and "rollers" would have to operate 
parallel to the length of the mountain wall, and the guiding tracks 
would have to run at right angles to it. 

When we began to use the compass and plot the measurements on the 
map, we found that our expectations were being met only in respect 
to the glide tracks. All signs of a rolling motion were at right 
angles to the direction we had expected. In other words, axles and 
track ran parallel ! 

We were in the position of the engineer who stands on the railroad 
tracks, and sees a locomotive travelling towards him. As it draws 
closer he suddenly discovers that the wheels are placed crosswise 
to the track, and that the axles run parallel to the rails. There- 
fore it is obvious that the machine cannot roll. Yet it does ! 
Should he jump to one side and out of the way ? Or shall he trust 
his theory that motion is impossible under such conditions and stay 



69 




70 



where he is, and perhaps get run over ? We jumped. But some 
five years later we regretted this cowardice, and returned to 
stand on the rails... 

There were, however, still many unsolved problems. Is it strange 
that we were unable to comprehend the behavior of a mountain range 
625 miles long in terms of lathe and locomotive ? 

Locality 6 . Boudinage, Lineation and "Early" Folding , Lemon 
Fa ir River Bluffs - LEAVE ALL HA^tMERS IN THE VEHICLES. All rele- 
vant features can be seen best on natural surfaces; the outcrop is 
unique and should be preserved from death by percussion . 

Bluff exposures are of interbedded white to grey marble 
and buff-to-brown ("chamois weathering") massive and "cleaved" dol- 
ostone, typical of Beldens member, Chipman formation, and structur- 
ally near the base of the Sudbury nappe. These rocks have been de- 
formed into a magnificant cascade of nearly-isoclinal (early) folds 
with associated structural features (see map. Figure 15). A synop- 
tic diagram of structural data for this locality (Station 7 of 
Voight, 1965) is given in Figure 16; early fold hinge lines trend 
toward the southeast at a low plunge, fold axial planes and assoc- 
iated secondary foliations dip eastward at a shallow angle, pene- 
trative lineations within the marble dip eastward, neck lines of 
boudins plunge northward at a shallow angle. 

Boudins thus have a different trend than early fold hinge 
lines, and are somewhat younger structures than the fold hinges; 
locally fold hinges are pinched-off, although maximum development 
occurs on fold limbs (Figure 17). Nonetheless, boudins are assign- 
ed to an early deformational event; their evolution appears to be 
related to the development of the secondary foliation associated 
with the early folds. The enormous ductility of marble inferred 
from the boudins is characteristic of early deformation, and devel- 
opment of boudinage can be logically envisaged as the result of 
continued compression of isoclinally folded structures. A detailed 
sketch of boudins at this outcrop is given in Figure 18, with num- 
bers assigned with reference to Figure 15. The smoothly-tapered 
boudin geometry had earlier led one mis-informed geologist to con- 
clude that the massive dolostone layers were extremely ductile dur- 
ing conditions of deformation (Voight, 1964a; 1965) , a conclusion 
having some significance with regard to the inferred deformational 
environment and to the inferred mechanics of formation. However, 
inspection of the boudins themselves shows clearly that the mode 
of deformation of the dolostone layers has been by pervasive brit- 
tle fracture and fragmentation; the pseudo-" rounded" boudin geo- 
metry appears as a consequence of fragmentation and (predominantly) 
calcite vein filling. The characteristic buff-weathering of the 
dolomite tends locally to mask the degree of fragmentation and vein 
filling in boudin necks, although the "thread-scored beeswax" pat- 
terns on the weathered surface are, in point of fact, fracture trac- 



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Figure 16. Synoptic diagram of structural data, Schmidt Net, 
for Locality 6, Fold hinge lines (small circles), 
pole to TTSi (large circle), pole to "n-Sp (crossed 
circle), neckline 13% maxima (lined pattern), 
bedding pole (S.) 10% maxima (dotted pattern), 
secondary foliation pole (S2) 10% maxima (crosses), 
penetrative lineation 27% maxima (triangles). 



7* 




Figure 17. Schematic block diagram of isoclinal folds, 

boudinage, foliation, penetrative lineation for 
Locality 6, 



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es on that surface . 

Boudins can be utilized in strain and ductility measure- 
ments according to a simple procedure outlined by Voight (1964a) . 
In the description hero, two-dimensional analysis is assumed ap- 
propriate. 

The neck (constriction) separating contiguous boudins is 

treated, assuming zero axial strain, constant volume in deformation, 

and an original layer thickness (t_) not less than maximum boudin 

thickness. Original neck width (W„ ) is given by 

"o 

(1) W = A /t , where A represents neck area, easily derived from 

n^ no n 

planimeter-measured tracings of down-axis boudin photographs. 

Average strain at the neck (6 ) obtains: 

n 

(2) e„ « (W - W ) / W ; the existing neck width is W . 

n n no n^ n 

If boudins are isolated, their separation is indicative of 
matrix strain; minimum values may be computed. By restoring boud- 
ins to their positions at initial separation, average boudin-layer 
strain is determinable. If A. equals individual boudin area in an 
array, tlie equation: ^ 

(3) W^ = (i A.) / t^ 

i = 1 
provides width of an assumed original layer of constant thickness. 
Coupling this dimension with the extended width (W) of the boudin 
layer gives: 

(4) e = (W - W ) / W . 

o o 

Longitudinal strain values for both boudin and matrix layers pro- 
vide data on rock ductility during deformation. The limiting thick- 
ness ration, t /t , where t is the minimum thickness of the neck, 
also serves as a measure of'^ductility for boudins which have devel- 
oped as a consequence of continuous flow. An example of this kind 
is given in Figure 19. 

Total cross-sectional area for necks 11 to 17 is about 11.5 
sq. ft.; cumulative width is 24.1 ft.; the "best estimate" of ini- 
tial thickness is 1.1 ft. From equation (3), cumulative initial 
width is 11.5/1.1 = 10.5 ft. Minimum(local) extensile strain in 
the marble "matrix", from equation (4), is ((24.1 - 10.5)/10.5) 100 
= 131%. Restored width at incipient separation is about 19.7 ft.; 
hence average dolomite (boudin layer) strain is ((19.7 - 10.5)/10.5) 
100 = 88%. In this.«xample no corrections were made for vein fill- 
ings, hence the calculated values are minimum values. 

Note that the spacing between necks is reasonjUaly consis- 
tent within individual layers, but extremely variable when one lay- 
er is compared with another. The critical factors controlling spac- 
ing include both material properties and geometric properties; in a 



77 






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locale characterized by repeated layers with ^^^^l^l^^lUll''^^ 
orooerties and boundary conditions, spacing varies primaril/ as 
a function of boudin-layer and matrix-layer thickness variations. 

A preliminary account of boudin mechanics has been given 
by Voight (1965); in that study an attempt was made (not without 
error) to theoretically account for such phenomena as soacinq of 
Soudins Figure 20, taken from that study, includes data from 
this localit?; the data have not been corrected for vein fillings. 
Portions of this work on boudin mechanics have since been revised 
but remain unpublished. 

A distinctive east-to southeast-trending lineation is 
oresent within the plane of secondary foliation; these lineations 
are penetrative; they are not restricted to discrete surfaces and 
Sey'dS not simply represent ordinary sUckensides P-^^-'^^^^V 
late-sta^^flexural fold deformation. Development of the linea 
tion IS lyngenetic with secondary foliation, and hence with early 
folding and boudinagc. 

The mean orientations of neck lines (i.e., boudins) and 
penetrative lineations are aporoximately orthogonal ^tr.os^ local 
ttils (cf. Figures 21, 22), and this relationship is general!/ 
oorne out by individual field observations ^^^^^^ P^^J^^^ij^f ,^'^1 
eation and well-developed boudins occur m association. T>^^^^^ 
lationship is interpreted to suggest that the penetrative linea- 
ttois represent the direction of principal extension -th- ^he 
Diane of flattening. Locally, distorted fossils can be found 
Sitch seem to reinforce this^iew. Planispiral gastropods found 
at this locality were elongated parallel to penetrative lineations 
and perpendicular to boudin axes. 

Return to automobiles and drive eastward to the Webster 
school. continue across Route 30, on Route 73 in ^he direction_ 
of Brandon. Continue past Mrs. Selleck s ^-eneral J^ore on Plea 
sant Brook, where a limited but fine selection °f Vermont cheese 
was always available for a hungry geologist, to School No. i. 
Distance from Webster School about 1.2 miles. 

Locality 7. Parautochthon and Aut ochthon: Paid Hill,. 

Stony Hil l. Mille r -Hi ll, and Vicinity - B eginning at che western 
IdF e of Figures 2i and i4, reference' s made to the nearly contin- 
uous bluff ^f white marble, which can be traced from Route 30 

(south of the Webster School) to a ^i^g^^^^J^^^fli/S^"" over- 
yards west of School Mo. IMcf. Figures 8, 23). The marble over 

r-fhF-following may be of assistance to the reader in understanding 
the descriptions of the Bald Hill area. Figures 23 and 24 Ref 
erence: 7 1/2' U.S.G.S. Sudbury, Vermont, ^^f ""jj^ * ^^^^^^Jer 
Hill area is traversed by Route 73, passing from the Seth Warner 
Memorial Highway at the Webster School, to Brandon. South of Route 
73 is Stony Hill (800 ft. contour); north of ^oute 73 ^^ "^^^/J^' 
and Bald Hill (713 ft. elev.); east of Stony Hill and Route 73 is 
Miller Hill. 



79 




OS lO 1.5 20 

initial boudin layer thickness (to) 



Figure 20. Initial (restored) boudin width versus initial 
boudin layer thicJcness, Station ? of this 
figure corresponds to Excursion Locality 6. 



80 




^ irure 21. Synoptic diagram of boudin maxims, Sudbury 
nappe I Station 8 data (Miller Hill klippe) 
given for original (split circle) and rotated 
(circled dots) positions. 



81 




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Fifcure 22, Synoptic diagram of penetrative lineation 
maxima, Sudbury nappe. 



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lies and truncates the contact of slate and mid-Ordovician lime- 
stones in the synclinorium core. This is the Sudbury thrust of 
Cady (1945, p. 570). The thrust contact is exposed locally; a 
20" dip discordance exists between the thrust and foliation. 

To the east, structural relationships seem more complex. 
In western ledges of Hill 641, Beldens marble appears to grade 
stratigraphically-upward into Middlebury limestone across a con- 
tact sub-parallel to dolomite bedding and secondary foliation. A 
typical sequence is as follows: beginning with the oldest, (1) 
white marble with massive dolostone beds seems to grade into (2) 
blue-grey calcite marble with massive dolostone, to (3) blue-grey 
marble, to (4) sugary-textured slightly argillaceous calcisiltite , 
often dolomitic, to (5) argillicalcilutite , typical of Middlebury 
limestone. The section is inverted at Hill 641; the contact can 
be traced to Brandon Swcimp , and appears to be essentially strati- 
graphic although subjected to large strains; there seems to be no 
evidence for an unconformity as suggested by Zen (1961, p. 321). 

The summits of Bald Hill and Hill 641 are interpreted as 
containing the overturned limb of a recumbent anticline with a 
core of Beldens marble. Amplitude exceeds one mile, and is of 
course much greater if this structure is continuous with the main 
body of the Sudbury nappe. Several smaller structures exposed on 
the north flank of Bald Hill, possibly recumbent anticlines, or 
nappes (with basal shear zones) , have similar characteristics of 
style (Figures 23, 25). The Sudbury nappe may be in fact complete- 
ly detached from subjacent structure, for field evidence is incon- 
clusive on this point; nonetheless a genetic relationship amongst 
these structures seems most likely, and they are regarded as par- 
asitic "digitations" on the overturned limb of the Middlebury syn- 
clinorium, here considered as a complex early fold. 

On the north slope of Stony Hill, a sliver of slate (of 
unknown age and origin) occurs athwart Route 73. The contact is 
well exposed about 200 feet south of the road, with foliation with- 
in both slate and marble approximately parallel to the southeast- 
dipping contact. Zen (1961, plate 1) shows this slate as a con- 
tinuous unit connected to the synclinorium core. Because of a 
small gap in outcrops, evidence to the contrary is not conclusive, 
but it favors no connection. The sliver is interpreted as either 
a thrust sliver, bounded top and bottom by "ductile" faults masked 
in secondary foliation. 

Further to the east, detailed relationships between marble 
and limestone have been literally uncovered by hand-dug excavations 
along the contact zone. Structural discordance has been observed 
at a small klippe on Miller Hill, in ledges 200 ft. north of the 
klippe, at the eastern foot of Miller Hill near Brandon swamp, and 
at the foot of Stony Hill west of Route 73. Some of the contact 
relationships are schematically shown in Figure 26, in which figure 
the effects of subsequent folding have been ignored. Near the 



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87 



"Spring House" (shown in the figure) west of Route 73, a subhori- 
zontal fault contact sharply truncates steeply-dipping bedding 
(dolostone and marble) within the Beldens marble. Similarly, a- 
cross Route 73, at the klippe, the fault truncates steeply-dip- 
ping, northeast-striking dolostone and marble layers. The rocks 
have been severely strained, as evidenced by inter-meshed boudins 
in the dolostone, superbly shown on the west face of the klippe*; 
much marble has been squeezed out in conjunction with boudinage 
evolution, which is presumed to be approximately synchronous with 
the large-scale low-angle thrust faulting. These outcrops seem 
to represent a dissected thrust plate — the Miller Hill thrust 
(Voight, 1965). 

The fault contact relationships vary as a function of 
rock type. South of the "spring house", in a bluff where more 
than fifty feet of continuous exposure occurs along the contact, 
a massive dolostone layer about one foot thick directly overlies 
the contact (Figure 26). Secondary foliation within marble and 
subjacent limestone essentially is parallel to the contact, which 
contact locally varies in attitude from vertical to sub-horizontal, 
presumably on account of subsequent folding. Despite this "appar- 
ent conformity" at the contact, rock flowage has been intense, as 
evidenced by broken fragments of dolomite within the marble; the 
dolomite beds have changed systematically in attitude, from an 
east-northeast strike, steeply-dipping attitude to virtual paral- 
lelism with the contact, a consequence of a "drag" effect associ- 
ated with the Miller Hill thrust. This thrust appears to be a 
discontinuity within a mass undergoing large strains, i.e., pre- 
sumably a discontinuity in terms of displacement, strain, and vel- 
ocity. Locally concordance or discordance may be apparent, de- 
pending upon the rheology (e.g., ductility) of the bordering rock. 
Within the environment of deformation associated with the Miller 
Hill and Sudbury thrusts, the def ormational mode for dolomite was 
by fracture; under identical conditions, calcite readily flowed. 
Hence where dolomite formed the predominant rock type, brittle 
fracture and discordant relations are observed; where marble pre- 
dominates, the contact relationships can seem to be concordant. 
Incidentally, it should be mentioned that there is some danger of 
misidentifying secondary foliation as bedding, particularly as 
thin-bedded limestone. Decisions concerning concordance or dis- 
cordance, which concern data on foliation rather than bedding, 
are to be interpreted cautiously. 

On the northern slope of Miller Hill, near the 550-foot 
contour, the marble unit appears to underlie the limestone. Thus 
a structural inversion of the marble-limestone contact apparently 
takes place at Miller Hill. The contact is definitely a fault 
contact in the vicinity of Route 73, but no definitive evidence 

* Boudin orientation is shown in Figure 24 ; by unrolling axes in 
small-circle paths about the "late" fold axis to account for rot- 
ation of the fault surface, the pre-folding orientations were re- 
constructed. An initial horizontal attitude of the folded surface 
was presumed. 



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favorable to either a concordant or discordant hypothesis was ob- 
served where the marble underlies limestone. 

Amongst other possibilities, the "inversion" could repre- 
sent a folded thrust, or a thrust plate of marble overlying a se- 
quence of marble and (younger) limestone in "normal" order. 

Part of the interpretation problem for the entire Bald 
Hill area arises from the fact that thrust relationships are rec- 
ognizable only where dissimilar rocks are in contact — and some- 
times not even under those conditions. IIo structural breaks are 
recognizable where marble rests upon marble, despite the fact that 
exposures are unusually good for this region, a locale of Alpine 
tectonics typically lacking alpine exposures. This is not to denv 
the existence of faults within the marble, only our ability to rec- 
ognize them; these faults are principally ductile phenomena, masked 
by and associated with the development of secondary foliation. 

A unique explanation satisfying all field relationships 
is not known to me. Two hypotheses are given here for purposes of 
discussion by excursion members (cf . Figure 28) : 

(A) double-nappe hypothesis; Miller Hill nappe overlies the 
Sudbury nappe; 

(B) single-nappe hypothesis; Miller Hill and Sudbury thrusts 
are part of a single structural element. 

Additional hypotheses or variants of the above may be suggested, 
none of which in detail have the attribute of simplicity. Ultimate- 
ly, however, it should be noted that the "key" to understanding the 
structure at this locality hinges on two units, the slate north of 
Stony Hill, and the limestone at Miller Hill. A blank cross-sec- 
tion, approximately an extension of line A' -A on Figure 23, is pro- 
vided for the excursion participants (Figure 29) in order to pro- 
vide an opportunity for individual interpretation based on the ev- 
idence presented at this stop. 

An overall view of the structure associated with "Sudbury 
nappe" is shown in Figure 30; the right side of this figure depicts 
the geology at Locality 7. and shows its assumed relationship to 
the structure of the Middlebury synclinorium and Taconic alloch- 
thon. 

Return west on Route 73 to Route 30; drive north 14 miles 
to Middlebury, Vermont, and junction Route 7. Park on north side. 
Otter Creek; walk to below falls. 

Interlude: This region marked a main route for the Algonquin and 
Troquois ; beginning on Lake Champlain (the Iroquois "Gate of the 
Country") , the route followed Otter Creek from Basin Harbor to its 



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headwaters. Here a portage followed, from the Vermont Valley 
across the Green Mountains to Weston, thence along the West Riv- ■ 
er to the Connecticut River at Brattleboro, southbound to Connec- 
ticut. Another main route followed the Lemon Fair River (Locali- 
ty 6.) from its headwaters to Lake Chcunplain; this route was used 
by Mohawks from the Hudson Valley.- The name Bomoseen means "big 
pond with grassy banks" in Abnaki language; the lake of that name 
(Locality 3.) was used by Algonquin and Iroquois to catch fish, 
which were smoked and carried to their permanent winter lodges. 
Certain parts of the Otter Creek and Champlain valleys were pre- 
viously occupied by peoples associated with the "Laurentian cult- 
ure"; Laurentian sites in New York have been dated at 2500-3000 
B.C. Little appears to be known of the ancient peoples, sometimes 
referred to as the "red paint" or "slate" culture; excavations of 
living sites had been carried out in Orwell by the Heye Foundation 
of the Museum of the American Indian, New York City, in 1933-35. 
A unique custom of the mourners was to place red hematite, symbol- 
ic of life, with their regarded dead. 

Locality 8 . East limb of the Middlebury Synclinorium; 
Middlebury Village - The critical Deldens-Middlebury contact has 
been traced northward from the Bald Hill vicinity in order to see 
if the style of deformation evident at Bald Hill was present along 
the entire eastern edge of the Middlebury synclinorium. Much of 
this contact is covered, but where exposures permit, the contact 
seems to dip moderately eastward, generally approximately parallel 
to secondary foliation. 

As an example, a locality several hundred feet west of 
Middlebury Village will be examined. Beldens marble, containing 
superb exposures of north-trending boudins in thick massive dolo- 
stone beds, lies in inverted contact with Middlebury limestone 
on the north bank of Otter Creek below the falls (cf. Cady , 1945, 
Plate 4, Figure 3; Seely, 1910, p. 30, plate 39). Foliation par- 
allels the contact, dipping eastward at 40°. Absence of a transi- 
tional zone and profound attenuation of dolostone above the con- 
tact (as evidenced by boudinage) suggest a thrust contact involv- 
ing differential flow between the two rock units. The limestone 
below the thrust has very likely undergone strains on the same 
order as marble overlying the thrust, as suggested by the presence 
of foliation; however its magnitude cannot be estimated in the ab- 
sence of structural elements such as boudinage. 

Field observations show that the Beldens marble - Middle- 
bury limestone contact is inverted throughout the east synclinor- 
ium limb (Voight, 1964b) , and suggest that phenomena described at 
Bald Hill are not restricted to that locality. The observed re- 
lationships are compatible with the hypothesis that the sequence 
Bascom formation - Middlebury limestone is involved in (or com- 
prises) a "root" zone characterized by differential, and locally 
discontinuous, flow (Figure 30). The "root" is taken to be that 



94 



zone from which a nappe arises, and as such, in the present in- 
stance, represents a zone of detachment between the nappes and 
less extremely deformed foreland rocks of the synclinorium east 
limb. 

Take Route 7 toward Burlington, 33 miles to the north. 

Interlude ; It's fun to watch the way they're made. 

They wasn't built by grafters; 
The cords , the uprights , oak -hewed pins , 

The ridge pole and the rafters ; 
An iron bridge turns rusty red 

A concrete bridge gets sooty; 
Give me a good old covered bridge 

For business, love, or beauty. 

Locality 9 . The Synclinorium core; Ledge Creek section . 
(To be visited if time permits.) - Inversion of contacts extends 
to the synclinorium core, and can be demonstrated, e.g., at Ledge 
Creek, 3 miles northwest of Middlebury Village. Here, with about 
a quarter-mile of continuous exposure, the Glens Falls limes tone- 
Hortonville slate section can be studied from the west to the 
east limb of the Middlebury synclinorium. East-dipping early fol- 
iation is consistent with an axial-plane relationship to the over- 
turned section, which seems precisely as shown by Augustus Wing 
( see Cady , 1945, Figure 2) in a section drawn approximately 
through this same locality. The synclinorium is not merely a late, 
relatively open fold structure, the concept apparently accepted by 
many workers of recent vintage, but has an origin dating back to 
the development of isoclinal fold structures, associated folia- 
tions, and ductile faults such as the Miller Hill thrust. 

Interlude: Reader, what I have here written, is not a Fiction, 
Flam, Whim, or any sinister Design, either to impose upon the Ig- 
norant, or Credulous, or to curry Favor with the Rich and Mighty, 
but in meer Pity and pure Compassion to the Numbers of Poor Lab- 
ouring Men, Women, and Children in (New) England, half sterv'd, 
visible in their meagre looks, that are continually wandering up 
and down looking for Employment without finding any, who here need 
not lie idle a moment, nor want Encouragement or Reward for their 
Work, much less Vagabond or Drone about it. Here are no Beggars 
to be seen (it is a Shame and Disgrace to the State that there are 
so many in England) nor indeed have any here the least Occasion 
or Temptation to take up that Scandalous Lazy Life. 



95 



REFERENCES CITED 

Cady, W. M. , 1945, Stratigraphy and structure of west-central 
Vermont: Geol. Soc. America Bull., v. 56, p. 515-558. 

, and Zen, E-an, 1960, Stratigraphic relationships of the 

Lower Ordovician Chipman formation in west-central Vermont: 
Amer. Jour. Sci., v. 258, p. 728-739. 

Crosby, G. , 1963, Structural evolution of the Middlebury Synclin- 
orium, west-central Vermont (abstract) : Geol. Soc. America Ann. 
Mtg. Program, p. 3 7A. 

Gushing, H. P., and Ruedemann, R. , 1914, Geology of Saratoga 
Springs and Vicinity: N. Y. State Museum Bull. 169, 177 p. 

Dale, T. N. , 1899, The slate belt of eastern New York and western 
Vermont: U. S. Geol. Survey Ann. Rept. 19, pt. 3, p. 163-307. 

, 1904, The geology of the north end of the Taconic Range: 

Amer. Jour. Sci., 4th ser., v. 17, p. 185-190. 

, 1912b, The Ordovician outlier at Hyde Manor in Sudbury, 

Vt. : Amer. Jour. Sci., 4th ser., v. 33, p. 97-102. 

, 1913, Ibid . (second paper): Amer. Jour. Sci., 4th ser., v. 

IS", p. 395^I5¥. 

Harper, C. , 1968, Isotopic ages from the Appalachians and their 
Tectonic significance: Canad. Jour. Earth Sci., v. 71, p. 162- 
195. 

Kaiser, E. P., 1945, Northern end of the Taconic thrust sheet in 
western Vermont: Geol. Soc. America Bull., v. 56, p. 1079-1098. 

Kay, M. , 1959, Excursions at the north end of the Taconic Range 
near Sudbury: p. 17-18, in Zen, E. , editor , 51st New England 
Intercollegiate Geol. CoiTT. , Rutland, Vt. , 85 p. 

Keith, A., 1912, New evidence on the Taconic question (abstract): 
Geol. Soc. America Bull., v. 23, p. 720-721. 

, 1913, Further discoveries in the Taconic Mountains (abstract): 



Geol. Soc. America Bull., v. 24, p. 680. 

, 1932, Stratigraphy and structure of northwestern Vermont: 

Washington Acad. Sci. Jour., v. 22, p. 357-379, 393-406. 

, 1933, Outline of the structure and stratigraphy of north- 
western Vermont: 16th Internat. Geol. Cong. Guidebook I, p. 4 8- 
61. 



96 



Seely, H. M. , 1910, Preliminary report on the geology of Addison 



County: Vt. State Geol., 7th Ropt. 



275-313, 



Voight, B. , 19643, Boudinage: a natural strain and ductility 

gauge in deformed rocks: Geol. Soc. America Annual Meeting Pro- 
gram, Miami Beach; p. 213-214 in_ Geol. Soc. America Spec. Paper 
82, 400 p. 

, 1964b, Structural relationships of the Sudbury Nappe to the 



subjacent Middlebury synclinorium and superjacent Taconic alloch- 
thon in west-central Vermont: Geol. Soc. America Annual Meeting 
Program, Miami Beach; p. 214-215 i_n Geol. Soc. America Spec. 
Paper 82, 400 p. 

, 1965, Structural studies in v/est-central Vermont: Ph.D. 



dissertation, Columbia University, New York City. 

Wright, W. H., 1970, Rock deformation in the slate belt of west- 
central Vermont: Ph.D. dissertation, Univ. of Illinois, Urbana, 
91 p. 

Zen, E. , 1959, Stratigraphy and structure of the north end of the 
Taconic Range and adjacent areas: p. 1-16, in Zen, E. , editor , 
51st Now England Intercollegiate Geol. Conf., Rutland, Vt., 
85 p. 

, 1961, Stratigraphy and structure at the north end of the 

Taconic Range in west-central Vermont: Geol. Soc. America Bull., 
V. 72, p. 293-338. 

, 1967, Time and Space Relationships of the Taconic Alloch- 

thon and Autochthon: Geol. Soc. America Spec. Paper 97, 107 p. 




Plate 1 . Polished cross- 
section across the "neck" 
of a dolostone boudin from 
Locality 6. Dolostone is 
dark grey, calcite and 
quartz veins are white, 
marble (matrix) is light 
grey. The fragmentation 
and brittle fracture of 
dolostone within the neck 
region is well shown; un- 
der the "same" conditions, 
the surrounding calcite 
marble layers deformed by 
f lowage. 



97 

Trip B-4 
THE CHAMPLAirJ THRUST A?^D RELATED FEATURES NEAR MIDDLEBURY, VERMONT 

by 

Peter J. Coney, Robert E. Powell, 

Marilyn E. Tennyson, Brewster Baldwin 

Department of Geology, Middlebury College 

Middlebury , Vermont 

This field trip will review preliminary results from investi- 
gations of the Champlain thrust, Middlebury synclinorium, and Green 
Mountain anticlinorium near the latitude of Middlebury by senior 
geology majors at Middlebury College. During the past seven years 
20 senior theses have been completed; seven of these provide a near- 
ly continuous geologic map of the Champlain thrust belt between 
Vergennes and Route 125 west of Middlebury at a scale of 500 feet 
to the inch. Other theses have included regional and local gravity 
studies, geologic mapping of critical localities in the Middlebury 
synclinorium and Green Mountain anticlinorium, petrologic studies 
of greenstone and ultramafic bodies east of the anticlinorium, sed- 
imentological studies of lower Paleozoic rocks, and mapping and 
petrologic studies of Mesozoic igneous rocks. These efforts have 
built upon earlier studies in west-central Vermont by Cadv (1945) , 
Welby (1961) , Osberg (1952) , and the unfortunately unpublished work 
of Crosby (1963) . Although the field trip will concentrate on the 
Champlain thrust west of Middlebury (Figure 1) , the regional tec- 
tonic setting of the thrust is briefly discussed here as background 
for participants. 

TECTONIC SETTING 

At the latitude of Middlebury four distinct tectonic provin- 
ces are from west to east: the Adirondack massif, the Lake Cham- 
plain lowland, the Middlebury synclinorium bounded on its west side 
by the Champlain thrust belt, and the Green Mountain anticlinorium. 
The tectonic significance of the Champlain thrust must be sought in 
the nature of these provinces and their boundaries. 

In the Lake Champlain lowland (Welby, 1961) a relatively un- 
deformed 5,000 foot sequence of Upper Cambrian through Middle Ordo- 
vician clastic and mainly carbonate shelf assemblage rocks rest 
with profound unconformity on a crystalline Precambrian basement 
(Figure 2) . The Precambrian is extensively exoosed in the Adiron- 
dack massif. The boundary between the Adirondacks and the lowland 
is a complex of fault blocks, down-faulted to the east, and struc- 
tural relief on the Precambrian basement is at least 5,000 feet. 

To the east of the Champlain lowland an Eocambrian to Middle 
Ordovician clastic and mainly carbonate shelf assemblage nearly 
10,000 feet thick presumably rests on Precambrian basement (Figure 



98 



ROUTE MAP FOR FIELD TRIP B-4 



M 



NEIGC, 1972 



mn. 



AT- 



, • 1 1 

• •ill ,1 



slate 
€-0 carbonate 
tv!-:-: € quartzit* 



\l 



t 



Ottar 1 



c Champlain thrust 

Orwsll thrust 

s St. Osorgs thrust 



fisid trip routs 



— 44* 



MIddlsbury 



• t«rt 



milat 



9 



FIG. I 







99 



Xbtrville Sht)e 

anJ dttomitit tihsianei 



S^ony Po\nt Sha)e 



'^^^ MothnyiDe S)il* - l»t,k ,U>i 



G)gnf trails J-imtt>»nt: 

ttttyreJ hmesttnt ■ et)e>it '€im 

inTSTTbur^ LimtsUnr: (Mln-^rJdtJ, i'n<tmp»t»nt, hlvi-^rti 
Jomeuihjit Jttomih'c limtsttnf 



Bridporf Dol«iton«.' 
\m t© brown 



tin J,). tmJ 
Uil>,1t m»rklt 




k/ «. w.tli r,/*y /-.it 



limnttnt doloticnt, futrftitt 



urch*r3s Ls.: fr^y /i ^./% eurj/f, J J,l 



iJ 



CuUinf Dolotfone: 

) imetttnt i nd dtlttlont ; ch«r^u m ufper p»ri ; 
trnjtttne w'ifh breecit fi Sflithrt (utrm hiltl) at tj<f 

Shelburne Marblf. 

i««hi>« m»rbl<; <'fA^ 1f^ /"^fStene , Jute de)»it»n* 



Clarendon Springs 'Do)oston€ : 



Dtnbu Forma.\ien : {- Pthdim) 

Kpptr p*rt (\^i)h'ntjj»ri Member) m«j/)y doUttont 

Wt'noojki Di)osfon«: 

pinK, crf»ifi, rnj ^ r*^ ; beds < I', fti^llf ItminMteJ. 

rionkttn OuarYi-itt : V*/<if>»^ »i" 



Dunham DaJostone: 

doUsfonf uifh KitjtreJ ^ojrri ^ tfmt 



Cheshire Ouart^iiit- 



/«u/fi- .^00 * ii/-«k>n-wr«t''>rri 



r/i/<» 



na Schiiftu f t/^ 



3.3jIJw1'», y-*r 



ffG. 2. Sequence of straka near Clid^U^ury,\fL 

CompHed from CaJuj'iHS'; Kai/ And CadyJ?'/? CaJ^ and Zen, 1940. U«lby, I'Jt/. 



100 



2). This sequence is rather intensely deformed into the south- 
plunging, westward inclined, Middlebury synclinorium (Cady, 1945). 
The two disparate early Paleozoic shelf assemblages of the Lake 
Cheimplain lowland and the Middlebury synclinorium (Figure 2) are 
separated by the Champlain thrust belt. The thrust belt is a ser- 
ies of east-dipping, low-angle faults which can be traced from at 
least southwestern Vermont and the adjacent Mew York northward 
into Canada (Cady, 1969). 

The Green Mountain anticlinorium (Cady, 1945) rises sharply 
just east of the Middlebury synclinorium and is a wast-vergent , 
doubly plunging, complex anticlinorium with an exposed core of 
Precambrian Mount Holly basement (Figure 3) . Structural relief 
on the Precambrian unconformity between the floor of the Middle- 
bury synclinorium and the crest of the anticlinorium is at least 
3 miles, and probably as much as 6 miles, in an east-west distance 
of about 8 miles (Powell, 1969; Tennyson, 1970). The boundary be- 
tween the synclinorium and the anticlinorium at the surface is loc- 
ally marked by east-dipping thrusts, but is mainly a descending 
cascade of west-vergent folds (Osberg, 19 52; Tennyson, 19 70) 
termed the Green Mountain front. 

The Green Mountain front is a major stratigraohic as well as 
tectonic boundary marking an abrupt facies change in Eocambrian 
to Ordovician rocks from the mainly carbonate miogeoclinal shelf 
assemblage on the west to "eugeoclinal" graywacke assemblage on 
the east. The Taconic "klippe", also of the eastern eugeoclinal 
facies, now lies athwart the Middlebury synclinorium on top of 
shelf rocks of the same age to the south of Middlebury, but has 
been removed by erosion northward. 

With the exception, presumably, of the Chester dome, no bona 
fide "Yankee" Precambrian cratonic basement is known east of the 
Green Mountain anticlinorium. Significantly a belt of serpentin- 
ized dunites (Beyer, 1972) and meta-greenstones (Crocker, 1972; 
Doolan and others, in preparation) lie just east of the anticli- 
norium embedded in meta-graywackes of the early Paleozoic "eugeo- 
clinal" assemblage. These rocks certainly mark a most significant 
tectonic boundary. It would appear, thus, the entire lower Paleo- 
zoic North American continental margin assemblage is exposed in a 
belt now less than 50 miles wide. Putting it another way, in the 
context of current plate tectonic theory, once one takes a single 
step east of the Green Mountain anticlinorium everything to the 
Bay of Maine is of suspect geo-political allegiance. 

An unconformity of late Middle Ordovician age seen at one 
place or another in most of the region, including the Taconic 
"klippe", separates the apparently west-derived shelf and "eugeo- 
clinal" assemblage from an apparently east-derived detrital-shale 
assemblage. The critical overlying rocks are the Hortonville 
Formation in the Middlebury synclinorium, the Pawlet Formation in 
the Taconic "klippe" (Zen, 1962) , and the Moretown Formation east 



lUl 




^ 



• "» o •» o 

• - « ri n 

E ' I I < 



102 



of the Green Mountain anticlinorium. Silurian-Devonian detrital 
rocks mask all prior tectonic relationships east of the Moretown 
Formation to the Ordovician Oliverian volcanic arc along the 
Vermont-New Hampshire border (Rodgers, 19 70), the presumed source 
of the detrital-shale flood. Very preliminary studies by Sedgwick 
(1972) suggest the Moretown Formation has a distinctly different 
heavy mineral assemblage compared to all older west-derived shelf 
and "eugeoclinal" rocks sampled to date. 

The Champlain and related thrusts and the folds in the Mid- 
dlebury synclinorium involve rocks as young as late Middle Ordovi- 
cian. The east side of the Green Mountain anticlinorium is often 
argued to involve Silurian-Devonian rocks as well (Cady, 1968). 
If all these major structures have any genetic relationship to one 
another, as is generally assumed, much deformation is as young as 
Acadian (Middle Devonian) at least. The emplacement of the Tacon- 
ic "klippe" is well documented as Taconic (Middle Ordovician) and 
numerous ductile folds and minor structures beneath and adjacent 
to the "klippe" in synclinorium rocks are correlated with this em- 
placement (Crosby, 1963). All these "Taconic" structures, includ- 
ing the "klippe" (Crosby, 1963; Johnson, 1970) are redeformed by 
younger more "brittle" deformation thought to be Acadian (Crosby, 
1963). The Middlebury region, then, has suffered at least two 
deformations. To what extent these phases were discrete events 
or a single continuum is yet to be resolved. 



THE CHAMPLAIN AND RELATED THRUSTS 

General Statement . The Champlain and related faults form a belt 
of east-dipping, low-angle thrusts which separate the Middlebury 
synclinorium on the east from the Lake Champlain lowland to the 
west. The belt of thrusts brings up resistant rocks, such as 
Cambrian Monkton Formation quartzite, which have produced a line 
of hills and ridges. Snake and Buck Mountains are the prominent 
ridges at the latitude of Middlebury. The system of faults forms 
a tightly packed series of slices exposed in a belt seldom more 
than 2 miles wide. The Champlain thrust is the most easterly of 
the faults while the other faults lie just west of, and structur- 
ally below, the Champlain thrust. For regional stratigraphic de- 
tail the reader is referred to Cady (1945) and Welby (1961) , and 
to Figure 2. 

Champlain Thrust . The Champlain thrust (Stop 3) enters the area 
at the north end of Buck Mountain and extends southward for at 
least 15 miles to Route 125 west of Middlebury. The fault can 
be easily traced northward into Canada, but its fate south of 
Route 125 is still in question (Stop 5) . Cady (1945) and the 
Centennial Geologic Map of Vermont (Doll and others, 1961) termin- 
ate it in the very poorly exposed south-plunging anticline just 
west of Cornwall several miles south of Route 125. Over almost 
the entire trace west of Middlebury, Cambrian Monkton Formation is 



103 



thrust over highly deformed Ordovician carbonate and shale. 

The thrust plane lies within several hundred feet of the base 
of the Monkton Formation and only at the south end of Buck Mountain 
(Cady, 1945; Welby, 1961; Egan , 1968) does it bite lower into sev- 
eral tens of feet of Dunham Dolostone. The Monkton Formation on 
the upper plate generally dips gently eastward into the Middleburv 
synclinorium forming a prominent dip slope on the east sides of 
Buck and Snake Mountains. Near the fault trace, however, local im- 
brications and folds are evident in Monkton Formation layers. The 
fault plane is only rarely exnosed, but at several points on Buck 
and Snake Mountains dips between 7 and 25 degrees eastward are 
seen. 

The trace of the fault wanders in topography and has right 
en echelon offsets from the north end of Buck Mountain south to 
Snake Mountain. South of the summit of Snake Mountain it trends 
southward then angles southeasterly until lost beneath glacial 
cover south of Route 125. The en echelon offsets result in a ser- 
ies of salients and re-entrants. Structure contouring on the 
fault surface (Westervelt, 1967) , gravity studies and geologic 
mapping (Davidson, 1970) suggest the salients are shallow down- 
warps and the re-entrants are mainly up-warps . Thus, the marked 
offsets are apparently primarily due to topographic expression of 
undulations in the fault plane rather than numerous cross-faults 
as shown on earlier maps (Welby, 1961; Doll and others, 1961). 
The southern "termination" near Route 125, where the trace angles 
southeastward, is marked by a southward structural plunge of the 
Monkton Formation before it and the fault trace are buried by 
glacial cover. If the fault continues southward it must climb 
up-section to place higher units on the sole. If the fault in- 
deed terminates near Cornwall then the plunge of the Monkton is 
probably due to rapid decrease in dip separation into the anti- 
clinal core (Smith, 1972) . 

Stratigraphic separation on the fault reaches nearly 5,000 
feet. If the shallow dips of the fault surface are projected 
eastward beneath the Middlebury synclinorium, and reasonable re- 
constructions of geometry are made on the upper and lower plate, 
the dip separation is well over 10,000 feet. Depending on how 
far the Monkton Formation extended westward from its present ex- 
posures along the fault trace, the dip separation could be much 
more. If the fault terminates west of Cornwall this dip separa- 
tion must decrease rapidly to zero, but where last seen Monkton 
Formation must lie over at least Bridport Formation giving a 
stratigraphic separation of about 3,000 feet. 

Related Thrusts West of the Champlain Thrust . The lower plate of 
the Champlain thrust is made up of a series of thrust slices from 
north of Buck Mountain to its apparent termination near Route 125. 
South of Route 12 5 the lower thrusts angle to the southwest away 
from the last seen southeasterly trend of the Champlain thrust. 



lOif 



Rocks within the slices are generally intensely deformed into 
tight west-vergent folds. 

At the south, near Route 125 (Stop 5) , two thrusts are iden- 
tified. The most westerly is the St. George thrust (Cashman, P., 
1972; Cashman, S., 1972; Lyman, 1972) followed eastward by the Or- 
well thrust (Cady, 1945; Welby, 1961). The St. George thrust 
generally places Glens Falls Formation over Middle Ordovician 
shales whereas the Orwell thrust generally places Bridport Forma- 
tion over Glens Falls Formation. Mapping at the north and south 
ends of Snake Mountain suggests the thrusts become younger from 
west to east since the St. George thrust is truncated by the Or- 
well thrust and the Champlain thrust truncates both the Orwell 
and St. George thrusts (Cashman, P., 1972; Cashman, P. and others, 
1972; Cashman, S., 1972; Lyman, 1972). Dips on the fault planes 
of the two older thrusts vary. Of the two the St. George thrust 
often appears the steeper, and in several places it must exceed 
30°E. Dips on the Orwell thrust are horizontal at the Crane School 
"klippe", or salient (Cashman, S., 1972), but elsewhere may be 
close to 10°E. At the south end of Snake Mountain both thrusts are 
truncated by the Champlain thrust placing Monkton Formation direct- 
ly on Middle Ordovician shale north of the truncation. The Orwell 
thrust reappears from beneath the Champlain thrust on the north 
side of Snake Mountain and has been maoped northward to Buck Moun- 
tain. At Buck Mountain, particularly in the re-entrant north of 
the main summit, several small thrust slices lie between the Or- 
well and Chcimplain thrusts superimposing Bridport and Crown Point 
Formations in imbricate slices (Westervelt, 1967) . 

Although stratigraphic separations on the older thrusts are 
understandably less than those found on the Champlain thrust, dip 
separation on the Orwell thrust could be equally as large as that 
calculated for the Champlain thrust. In reality the soles of all 
these thrusts probably converge at depth beneath the Middlebury 
synclinorium. 

Folds and Minor Structures . Most folds found directly below the 
Champlain thrust (Stop 3) are tight f lexural-f low or passive folds 
usually inclined or overturned in westerly directions. A well 
developed axial surface "crenulation" or "fracture" cleavage is 
common, particularly in Crown Point limestones (Stop 3) . Directly 
above the Orwell thrust, particularly in Bridport dolostones and 
limestones, fold patterns are more complex (Stop 4). Trends of 
folds are generally northward, but locally axial traces sweep in- 
to more latitudinal trends. In many places the folded bedding, 
particularly just above the Orwell thrust, is truncated by thrust- 
ing and the folds seem to have developed before as well as during 
faulting. At no place, however, has the axial surface crenulation 
cleavage of the folds below the Champlain thrust been found to be 
deformed by any penetrative later cleavage. On the other hand, 
numerous overturned to recumbent folds with variable trends are 
found in Ordovician shales below the thrust belt. Some of these 



105 



have a well developed axial surface cleavage, but one large fold 
on the west face of Snake Mountain where the Champlain thrust 
lies directly on the shale, has a north-trending cleavage unrelat- 
ed to fold geometry (Lyman, 1972) . Crosby (1963) reports evidence 
of two deformations south of Route 125 in Bridport Formation on 
the upper plate of the Orwell thrust. In general, however, evi- 
dence for two "distinct" deformations so characteristic of the 
Middlebury synclinorium to the east of the thrust belt is not so 
obvious in and west of the thrust belt. 



GRAVITY DATA 

About 500 gravity stations have been made in the vicinity 
of Middlebuiry. The results thus far are very preliminary. Two 
east-west profiles by Powell (1969; Powell and Coney, 1969) be- 
tween the Adirondack Mountains and the east flank of the Green 
Mountain anticlinorium show a sharp, asymmetrical westward, gravi- 
ty high of nearly 50 milligals over the anticlinorium relative to 
a broad low over the Middlebury synclinorium and Lake Champlain 
lowland (Figure 3) . There is also a slight gravity high over the 
Adirondacks. The absolute Bouguer anomaly over the Green Mountains 
is only cibout -15 milligals which is anomalously high for continen- 
tal regions. These results are similar to those of Diment (1968) 
and Bean (1953) . It would appear that the structural relief dis- 
played on the Precambrian unconformity from the floor of the syn- 
clinorium to the crest of the anticlinorium also affects the en- 
tire crust bringing dense material to high levels beneath the 
anticlinorium. 

More detailed studies adjacent to the Champlain thrust by 
Smith (1972) show a distinct south-trending trough-like gravity 
low of about 8 to 15 milligals just east of the trace of the Cham- 
plain thrust east of Snake Mountain. The trough appears to turn 
southwesterly at the south end of Snake Mountain migrating to a 
similar position just east of the Orwell thrust. It thus crosses 
the southeasterly projection of the last outcrops of the Champlain 
thrust at nearly 90°. 

Davidson (1970) carried out gravity studies and geologic map- 
ping in the offset of the Champlain thrust between Buck and Snake 
Mountains (Stop 4) where an east-west cross fault was mapped by 
Welby (1961) and shown on the state geologic map (Doll and others, 
1961) . Welby estimated the down to the south displacement on this 
cross fault at about 2,000 feet to explain the westward offset of 
the Champlain thrust from Buck to Snake Mountain. Considering the 
trace of the Orwell thrust less than 100 feet of dip separation 
on such a fault can be generated. Gravity contours trend norther- 
ly west of the thrust traces between Snake Mountain and Addison 
and northwesterly east of the thrust traces between Buck and Snake 
Mountain. These trends, combined with results from numerous com- 



106 



puter-generated gravity models, and the structural data, suggest 
the cross-fault is unnecessary. 

REGIONAL ASPECTS 

If the dip separation on the Champlain thrust belt is 
10,000 to 20,000 feet or more it becomes difficult to get rid of 
this displacement without driving the master sole thrust of the 
system into and beneath the Green Mountain anticlinorium offsett- 
ing the Precarabrian basement (Figure 3) (Powell, 1969; Tennyson, 
1970) . Judging from structure sections drawn across northern Ver- 
mont (Doll and others, 1961) and at the latitude of Brandon (Cros- 
by, 1963) south of Middlebury others reach similar conclusions. 
Several efforts to determine if the Champlain thrust system re-ap- 
pears out of the eastern flank of the synclinorium, passing in the 
air over the anticlinorium, have resulted in no evidence to sup- 
port such an option. This suggests the Champlain thrust belt, the 
Middlebury synclinorium, and the Green Mountain anticlinorium are 
inescapably linked in a strongly west-vergent tectonic system 
which drove the western cratonic foreland beneath the Champlain 
thrust belt and the west-vergent synclinorium-anticlinorium couple. 
Silurian-Devonian rocks seem to be involved in some way east of 
the anticlinorium. Thus, the massive eastward underthrusting and 
resultant couple, which based on gravity data must have involved 
the entire crust, are presumably in part at least "Acadian". 

At James Pasture (Stop 2) and elsewhere in the Middlebury 
synclinorium (Crosby, 1963; Soule, 1967) there is ample evidence 
of a northwest-trending early "ductile" deformation which produced 
recumbent flow-folds with penetrative axial surface "mineral" clea- 
vage. These structures are clearly deformed by later north-trend- 
ing folds and cleavage (Stop 2) , generally of a more "brittle" as- 
pect. A similar fabric is found in schists on the Green Mountain 
anticlinorium (Tennyson, 1970). The later deformation appears to 
produce some, but not all, of the main map pattern of the syncli- 
norium and anticlinorium. If the axial surface cleavage in folds 
found below the Champlain thrust is the same as the "late" clea- 
vage it often resembles in the synclinorium (which has not been 
proved) , it would appear the thrust belt developed sequentially 
west to east during and after most of the folding on both sides 
of the belt. Most workers conclude the early deformation was 
Taconic and relate it to emplacement of the Taconic "klippe". The 
later deformation is related to the Acadian and linked to the 
Chcimplain thrust and much of the gross geometry of the synclinor- 
ium-anticlinorium couple. Nothing in studies made thus far at 
Middlebury College refutes this general interpretation, but on the 
other hand neither does it prove it. Much remains to be done. 

Finally, a most interesting problem is what happens to about 
4,000 feet of Cambrian stratigraphy exposed in the Middlebury syn- 
clinorium which is missing in the Lake Chcunplain lowland. The 



107 



thrust belt appears to separate the two stratigraphies, and the 
thrust belt itself may have been controlled by the westward on-lap 
and thinning indicated by the facies change. Perhaps the initial 
thrust rode up a basement step on the base of one or another of 
the massive quartzite or dolostone struts breaking upward and out 
as the layers end to the west. On-going and future work will hope- 
fully clarify this and many other interesting problems. 

ACKNOWLEDGEf^ENTS 

The senior author is grateful to the students of geology at 
Middlebury College upon whose senior theses this report is based. 
Discussion with them during the course of their work brought fo- 
cus to many problems. My gratitude is expressed to Research Corp- 
oration which generously funded the gravimeter used in geophysical 
investigations and student field travel. Field excursions and 
discussions with Marshall Kay, WaUaoe M. Cady , Fred A. Donath, Ian 
W. Dalziel, and Charles G. Doll, and correspondence with John Rod- 
gers were most helpful. Close cooperation with Rolfe S. Stanley 
and Barry Doolan of the University of Vermont is much appreciated. 

ROAD LOG B-4 

Note: Exercise caution while driving on narrow, dirt, country 
roads, and at blind, busy intersections. Parking space 
at Stops is generally limited. Park off road and do not 
block farm entrances or gates. Road Log starts from 
parking lot east of Middlebury College Science Center. 

Miles 



0.0 Leave Science Center parking area heading north, turn left 
onto Franklin Street which turns quickly north toward 
Route 125. 

0.1 Stop. Turn right onto Route 125. 

0.2 Turn left onto Weybridge Street. 

1.0 Turn right following signs to Morgan Horse Farm. Chipman 
Hill at 1 o'clock. Chipman Hill rises 400 feet above the 
surrounding terrain and exposes no bedrock anywhere on its 
slopes. Gravity work over the feature suggests it is en- 
tirely of unconsolidated material, thus a glacial deposit, 
presumably a kame or drumlin. 

1.4 Bear left. Road to right crosses Pulp Mill covered bridge, 

1.8 Otter Creek on right. 



108 



2.7 Morgan Horse Farm on right. 

3.3 Road intersection. Continue straight. 

4.4 Descend into valley of Otter Creek. 

4.6 On skyline at 3 o'clock, axis of Green Mountain anticlin- 
orium. 

4.9 Cross iron bridge over Otter Creek at Weybridge-New Haven 
town line. Power dam on left at Huntington Falls. 

5.3 Stop 1: Folds in Middleb ury synclinorium . Park along 

right side of road near power pole. Cross fence and des- 
cend across small ravine. Proceed up low rise to east to 
pasture and lov; hill about 1,000 feet east of road. Ex- 
posed on the hill, and in adjacent woods is a series of 
north-trending westward inclined folds with a well devel- 
oped north-trending axial surface cleavage in limestones 
and dolos tones of the Chipman Formation. Several promin- 
ent dolostone layers and the distinctive banded Weybridge 
Member enable the fold geometry to be clearly seen. These 
structures are interpreted by Crosby (1963) as late struc- 
tures related to the gross geometry of the Middlebury syn- 
clinorium and probably Acadian in age. 

5.3 Return to car, continue north up hill. 

5.4 Turn sharp left at intersection. 

6.0 Snake Mountain ridge at 12 o'clock on skyline. 

6.2 Descend into valley of Otter Creek. Profile of Buck Moun- 
tain at 3 o'clock on skyline. 

6.9 Turn sharp left at road intersection. 

7.2 Turn left at intersection. Proceed across twin-bridges 
below Weybridge power dam and bear right. Continue south 
through Weybridge Village. 

9.1 Weybridge Elementary School on left; cemetery on right. 

9.3 Stop at yield sign. Then bear left onto Route 23 for 50 
yards, turn left onto gravel road just past church on left. 

9.9 Stop 2: Two deformations . Park at road intersection just 
before large white barn with two silos. Enter gate to pas- 
ture on northwest side of intersection. Please close gate 
after entering pasture. Proceed northwest across pasture 
toward low wooded ridge. No hammers, please. 



109 



This pasture, which lies in the core of the Middlebury 
synclinorium, was mapped by plane table by Crosby (1963) 
and lias since been mapped hundreds of times by students 
from Middlebury College and numerous other institutions 
in New England. It is certainly one of the finest dis- 
plays of multiple deformation geometry and fabric avail- 
able for instructional use, and is probably one of the 
key areas for interpretation of the tectonic evolution 
of the riiddlobury synclinorium. 

Exposed in the pasture are a number of very subtle north- 
west-trending recumbent folds with a distinct axial sur- 
face mineral cleavage. The geometry of these folds is 
outlined by the contact between the base of the Middle- 
bury Formation grey marbles and the top of the Beldens 
Formation dolostones and marbles. A thin grey slate just 
above the base of the Middlebury is a most useful marker. 
These folds and related cleavage arc clearly deformed by a 
north-trending set of small folds and a prominent axial 
surface "crenulation" cleavage. The assumption is that 
the late folds in this pasture are the same generation as 
the folds seen at stop 1. The early folds here are inter- 
preted as "Taconic". 

9.9 Return to cars, turn around and retrace route to Route 23. 

10.4 Stop. Turn right onto Route 23, bear to left of cemetery. 

10.8 At 9 o'clock, valley of Lemon Fair River. Beyond wide val- 
ley is the dip slope on Monkton Formation off the east side 
of Snake Mountain. The Champlain thrust lies just on oth- 
er side of skyline ridge dipping eastward beneath the Mid- 
dlebury synclinorium. 

11.1 Profile of Buck Mountain at 12 o'clock on skyline. 

11.5 Slow for sharp turn to left in road. 

13.4 Bridge over Lemon Fair River at confluence with Otter Creek 
on right. 

14.5 First of many outcrops of Monkton Formation red quartzites 
and shales at base of dip slope of Snake Mountain. 

15.1 Stop. Turn right onto Route 17. 

15.4 Bridge across Otter Creek. Prepare for dangerous left turn 
on blind hill dead ahead. 

15.6 Slow by white barn on right, then turn left off Route 17 on- 
to road leading north, just before red brick farmhouse on 
northeast side of intersection. 



no 



16.7 Buck Mountain at 12 o'clock. The Champlain thrust lies 
just below the cliffs west of sununit placing Monkton 
quartzites over Ordovician limestones and shales. The 
gentle east slope is a dip slope on f-tonkton Formation. 

18.3 Stop 3: Champlain Thrust . Park at cemetery. Walk east 

along north side of cemetery fence to east end of cemetery. 
Cross fence and enter juniper woodland and pasture and pro- 
ceed northeastward toward summit of Buck Mountain. The 
best route to the summit is up the northwest ridge on sky- 
line through grove of large hemlock trees. The walk to 
the summit first crosses outcrops of Orwell limestone on 
. the west flank o*f an overturned syncline. Glens Falls 
Formation, largely covered, is in the core. A minor 
thrust fault places Middlebury Formation limestones over 
the east flank of the fold. East of the thrust the Mid- 
dlebury limestones are caught in a tight overturned anti- 
cline with a well developed axial surface fracture clea- 
vage. An overturned syncline follows to the east with a 
core of Glens Falls Formation. The axis of the fold is 
just above the base of the steep slope rising to the sum- 
mit at about the 550-foot contour line. Continuing up 
the steep slope outcrops of Orwell appear followed quick- 
ly by Middlebury limestone, all here overturned to the 
west. Directly above the Middlebury limestone are out- 
crops of Monkton quartzites and dolostones, followed 
above and to the summit by red Monkton quartzites. The 
Champlain thrust lies between overturned Middlebury lime- 
stone and right side up Monkton quartzite. The trace of 
the thrust is exposed to the south at the foot of the 
quartzite cliffs. Excellent panoramic view from the sum- 
mit: Snake Mountain to the southwest, the Lake Champlain 
Lowland and the Adirondack Mountains to the west. Re- 
trace route to cemetery and cars. 

18.3 Turn around and return to Route 17. 

18.4 Profile of Snake Mountain at 1 o'clock. Champlain thrust 
lies at base of steep cliffs and slopes just below sky- 
line and dips about 7* east. 

20.9 Slow for right turn onto Route 17. 

21.3 Continue straight on Route 17 past junction from left of 
Route 23. 

21.5 Stop 4: Orwell Thrust . Park along north side of road 
near gate into pasture on right. Walk west along road to 
outcrops of Bridport dolostones on right. Just beyond to 
west is a large readout in Ordovician Stony Point shale. 
The Orwell thrust lies between the two exposures placing 
Bridport over Stony Point. If one enters woods and as- 



Ill 



cends hill north of road the fault trace can be followed 
to the summit of the hill in a pasture where Bridport 
caps the west face of the hill over shale. Good exposures 
of Bridport Formation in pasture. Looking south -southwest 
across road and valley to Snake Mountain from summit of 
hill the Orwell thrust lies several feet into woods at 
edge of hillside pasture. The Champlain thrust lies just 
above it descending from summit of Snake Mountain far to 
west. The Champlain thrust truncates the Orwell thrust 
several hundred yards to west and Monkton quartzite lies 
directly on shale from here to the west face of Snake 
Mountain. Note similar elevation of thrust traces north 
and south of road suggesting minor, if any, cross faulting. 
Return to cars. 

21.5 Continue west on Route 17. 

23.0 At 9 o'clock the Champlain thrust is exposed at base of 
quartzite cliffs near skyline ridge. Several caves which 
have formed in weak shale below the resistant quartzite 
provide excellent exposures of the overhanging fault plane 
and minor structures in shale below. 

23.3 Turn left off Route 17 onto gravel road leading south along 
west face of Snake Mountain. 

26.6 Turn left (east) on gravel road. 

27.1 At 3 o'clock. Crane School hill half a mile to south is 
either a klippe or tongue-like salient of the Orwell thrust 
placing Bridport and Crown Point Formations over Ordovician 
shales. At 10 o'clock, just to left of saddle on Snake 
Mountain ridge on skyline the Orwell and St. George thrusts 
are truncated by the Champlain thrust. 

2 8.0 Turn right at intersection. Orwell thrust "klippe" 
straight ahead. 

28.5 At 3 o'clock cliffs of folded Bridport Formation in woods 
just above Orwell thrust. 

2 8.8 Beehives on left. On right, lower slopes in pasture expose 
Ordoviciein shales below Orwell thrust. 

29.0 Slow for road junction. Turn left. 

29.2 Iberville shale exposed on knolls and hills surrounding 
farms. 

29.6 At about 10 o'clock Champlain thrust lies at foot of prom- 
inent cliffs of Monkton quartzite at edge of farmland. 



112 



29.7 Culvert across small creek. From this point to pass over 
Snake Mountain at 30.2 the route crosses all three thrusts. 

29.9 Road crosses Champlain thrust. Monkton Formation is ex- 
posed in small road cuts and in quarry at right on upper 
plate. 

30.2 Pass over Snake Mountain. Shift to lower gear for steep, 
winding descent. 

30.6 Crossroads. Turn right (south). 

30.8 Winooski Formation exposed in cliffs on east side of road. 

31.9 First of many dip slope outcrops of Monkton Formation. 

32.4 Stop. Intersection with Route 125. Cemetery on right. 
Turn right. Around this intersection are the last and 
southernmost exposures of the Monkton Formation and the 
Champlain thrust which presumably angle southeasterly 
beneath glacial cover. 

32.8 At 3 o'clock cliff of well-bedded Monkton quartzites. At 
12 o'clock, and extending south, low hills are in Bridport 
and Crown Point Formations on upper plate of Orwell thrust 
here heading southwest. 

33.3 Continue on blacktop past dirt road to right. From here 
to 34.0 road passes complex relationships involving Orwell 
and St. George thrusts. At 33.5 road cuts on right expose 
Glens Falls Formation on upper plate of St. George thrust 
which angles nearly east-west up the brow of hill to north. 
On left at 33.9 outcrops of Bridport Formation on upper 
plate of Orwell thrust. 

34.5 Turn right (north) off Route 125 onto narrow blacktop. 

35.0 Intersection. Turn right. Good panorama of Snake Mountain 
to northeast. 

35.8 Stoy 5; St. George Thrust . Park in larger quarry in Ordo- 
viclan shales on right. Brief stop to examine the St. 
George thrust and minor structures in lower plate, and to 
view problem of the southern termination of the Champlain 
thrust. From quarry ascend into woods and then pasture to 
top of hill. Glens Falls Formation outcrops on north side 
of hill on upper plate of St. George thrust. From top of 
hill cliffs of Monkton Formation to east can be seen plung- 
ing southeastward into Lemon Fair valley. Champlain thrust 
is at foot of cliffs and hills. The thrust is lost from 
here southeastward beneath extensive glacial cover. Fol- 
low trace of St. George thrust east-northeast down hill to 



113 



streeim and dirt road. Both Orwell and St. George thrusts 
continue north of road on west face of long south-plung- 
ing ridge in woods. Turn left on dirt road and return to 
cars. 

35.8 Continue east along dirt road. 

36.3 Stop. Blind intersection with busy Route 125. Turn left 
(east) on Route 125. 

37.3 Slow down for sharp left turn on Route 125 after bridge 
over Lemon Fair River. 

38.3 Straight ahead are The Ledges, a prominent north-trending 
cliff exposing Bascom through Middlebury carbonates on 
west flank of Middlebury synclinorium. 

38.7 Slow for left bend amd winding ascent of The Ledges. 

39.8 Slow for right bend in road at ridge crest. 

40.0 Slow for hidden crossroad. Hortonville shales in core of 
Middlebury synclinorium exposed in small readouts and out- 
crops . 

41.8 Blinker light at edge of Middlebury College campus. 

42.0 Turn right opposite Catholic Church onto Franklin Street 
and Middlebury College Science Center. End of trip. 

REFERENCES CITED 

Bean, R. J., 1953, Relation of gravity anomalies to the geology of 
central Vermont and New Hampshire: Geol. Soc. America Bull., v. 
64, p. 509-538. 

Beyer, B. J., 1972, Petrology and origin of ultramafic bodies in 
Vermont (abs.): Vermont Acad. Arts and Sci., 7th Intercoll. Stu- 
dent Symp. , April; also unpubl. senior thesis, Middlebury Coll. 

Cady, W. M. , 1945, Stratigraphy and structure of west-central Ver- 
mont: Geol. Soc. America Bull., v. 56, p. 515-558. 

, 1968, Tectonic setting and mechanism of the Taconic slide: 



Amer. Jour. Sci., v. 266, p. 563-578. 

, 1969, Regional tectonic synthesis of northwestern New Eng- 

land and adjacent Quebec: Geol. Soc. America Mem. 120, 181 p. 

Cashman, P. H. , 1972, Structural geology of southern Snake Moun- 
tain, Addison County, Vermont: unpubl. senior thesis, Middle- 
bury Coll. 



11^ 



, Cashman, S. M. , and Lyman, T. J., 1972, Structural analy- 
sis of the Champlain thrust at Snake iMountain, Addison County, 
Vermont (abs.): Vermont Acad. Arts and Sci . , 7th Intercoll. 
Student Symp. , April. 

Cashman, S. M. , 19 72, Structural geology of the Crane School sal- 
ient and central Snake Mountain, Addison County, Vermont: 
unpubl. senior thesis, Middlebury Coll. 

Crocker, D. E. , 1972, Petrologic and tectonic analysis of the orth- 
ogeoclinal greenstones in Washington County, Vermont (abs.): 
Vermont Acad. Arts and Sci., 7th Intercoll. Student Symp., April, 
also unpubl. senior thesis, Middleburv Coll. 

Crosby, G. W. , 1963, Structural evolution of the Middlebury synclin- 
orium, west-central Vermont: unpubl. Ph.D. dissertation, Col- 
umbia Univ. , 136 p. 

Davidson, Gail, 1970, A new interpretation of Champlain thrust 
structure near Snake Mountain (abs.): Vermont Acad. Arts and 
Sci., 5th Intercoll. Student Symp., April, also unpubl. senior 
thesis, Middlebury Coll. 

Diment, W. H. , 1968, Gravity anomalies in northwestern New England, 
in: Zen, E-an, White, W. S., Hadley, J. B., and Thompson, J. B. , 
Jr., editors. Studies of Appalachian geology, northern and 
maritime (Billings vol.): New York, Wiley-Interscience , p. 399- 
413. 

Doll, C. G. , Cady, W. M. , Thompson, J. B. , Jr., and Billings, M. P., 
1961, Centennial geologic map of Vermont: Vermont Geol . Survey. 

Egan, R. T. , 1968, Structural geology of south of Buck Mountain, 

Addison County, Vermont: unpubl. senior thesis, Middlebury Coll. 

Johnson, A. H. , 1970, Structural and geochemical data from the Sun- 
set slice of the Taconic klippe near Orwell, Vermont (abs.): 
Vermont Acad. Arts and Sci., 5th Intercoll. Student Symp., April, 
also unpubl. senior thesis, Middlebury Coll. 

Lyman, Tracy, 19 72, Structural analysis of the Champlain thrust at 
north Snake Mountain, Addison County, Vermont: unpubl. senior 
thesis, Middlebury Coll. 

Osberg, P. H. , 1952, The Green Mountain anticlinorium in the vicin- 
ity of Rochester and East Middlebury, Vermont: Vermont Geol. 
Survey Bull. 5, 127 p. 

Powell, R. E. , 1969, Structural and gravity profiles of the Cham- 
plain Valley, Champlain thrust, and Green Mountain front, west- 
central Vermont: unpubl. senior thesis, Middlebury Coll. 



115 



, and Coney, P. J., 1969, Structural and gravity profiles 



of the Champlain Valley, Champlain thrust, and Green Mountain 
front, west-central Vermont: New York State Geol. Assoc. 
Guidebook to Field Excursions, 41st Ann. Mtg. , p. 148. 

Rodgers , John, 1970, The tectonics of the Appalachians: New York, 
Wiley-Interscience, 271 p. 

Sedgwick, G. B. , 1972, An analysis of the heavy mineral distribu- 
tion in central Vermont: unpubl. senior thesis, Middlebury 
Coll. 

Smith, P. L. , 1972, Gravity studies in the vicinity of Cornwall, 
Vermont: unpubl. senior thesis, Middlebury Coll. 

Soule, J. M. , 1967, Structural geology of a portion of the north 
end of the Middlebury synclinorium, Weybridge, Addison County, 
Vermont: unpubl. senior thesis, Middlebury Coll. 

Tennyson, Marilyn, 1970, Regional tectonics of west-central Ver- 
mont: unpubl. senior thesis, Middlebury Coll. 

Welby, C. W. , 1961, Bedrock geology of the central Champlain Val- 
ley of Vermont: Vermont Geol. Survey Bull. 14, 296 p. 

Wostervelt, Thomas, 1967, A structural analysis of the Champlain 
thrust at Buck Mountain, Addison County, Vermont: unpubl. 
senior thesis, Middlebury Coll. 

Zen, E-an, 1961, Stratigraphy and structure at the north end of 
the Taconic Range in west-central Vermont: Geol. Soc. America 
Bull. , V. 72, p. 293-333. 



117 



Trip B-5 

ANALYSIS AND CHRONOLOGY OF STRUCTURES ALONG THE CHAMPLAIN THRUST 
WEST OF THE HINESBURG SYNCLINORIUM 



by 

Rolfe Stanley and Arthur Sarkisian 
Department of Geology 
University of Vermont 

INTRODUCTION 

The Champlain thrust has long attracted the attention of 
geologists. Prior to the discovery of fossils along this belt 
the thrust was considered an unconformity between the strongly- 
tilted Ordovician shales of the "Hudson River Group" and the 
overlying, gently-inclined dolostones and sandstones of the "Red 
Sandrock Formation" (Dunham, Monkton, Winooski formations of Cady, 
1945) . The "Red Sandrock Formation" was thought to be Silurian 
in age since it was lithologically similar to the Medina Sand- 
stone of New York. Between 1847 and 1861 fossils of pre-Medina 
age were found in the "Red Sandrock Formation" and its equivalent 
"Quebec Group" in Canada. Based on this information, Hitchcock 
(1861, p. 340) stated that "it will be necessary to suppose the 
existence of a great fault, extending from Quebec through the 
whole of Canada and Vermont and perhaps to Alabama. Its course 
through Vermont would correspond very nearly to the western boun- 
dary of the red sandrock formation." Since then, although its 
extent has been greatly limited, its importance has not dimin- 
ished. 

Our understanding of the Champlain and associated thrusts 
is primarily the result of studies by Keith (1923, 1932), Clark 
(1934), Cady (1945), and Welby (1961). Current interest in 
earthquake research on the character, movement, chronology, and 
mechanics of faults requires a closer, more detailed study of 
such well mapped faults as the Champlain thrust. 

Acknowledgements 

The work of Cady (1945) and Welby (1961) along the Cham- 
plain thrust in western Vermont is very valuable in providing 
the framework for detailed work that is presently being done at 
the University of Vermont and Middlebury College. Although many 
geologists have contributed to our present understanding of this 
region, syntheses by Cady 1969, Doll and others 1961, Rodgers 
1968, and Zen 1967, 1968 are particularly helpful. 

Many students at the University of Vermont have contrib- 
uted information for the localities in this trip. Data on 
fractures, faults, and quartz deformation lamellae at the Shel- 



118 



burne Access Area were collected by Charles Rubins, John Mil- 
lett, Edward Kodl, Robert Kasvinsky, Evan Englund, and Jack 
Chase. The analyses at locality S9 and Mount Philo are large- 
ly the work of Arthur Sarkisian. Richard Gillespie, Roger 
Thompson, Jack Chase, Greg McHone, and Gary French provided in- 
formation for Pease Mountain. 



REGIONAL GEOLOGY 

The Champlain thrust extends for approximately 75 miles 
from Cornwall, Vermont, to Rosenberg, Canada, and places Lower 
Cambrian dolostone with some quartzite on highly deformed Mid- 
dle Ordovician shale and minor beds of carbonates. Throughout 
its northern part the thrust is confined to the lower member 
(Connors facies) of the Dunham Dolostone. At Burlington the 
thrust apparently rises 2000 feet in the section to the dolo- 
stones and quartzites of the lower part of the Monkton Quartzite. 
It then truncates major structure in the Ordovician rocks of the 
lower plate south of Mount Philo to Cornwall, Vermont (Doll and 
others, 1961). The upper part of the Dunham only reappears 
along the thrust just south of Buck Mountain (Welby, 1961). The 
Champlain thrust appears to be primarily restricted to the first 
massive dolostone interval above the Precambrian. 

Throughout most of its extent north of Pease Mountain 
(figure 1) the trace of the Champlain thrust is somewhat strai^t 
and the surface strikes to the north and dips gently to the east 
at angles less than 20 degrees. South of Pease Mountain the 
trace of the thrust is irregular because of subsequent folding 
and faulting (Doll and others 1961, Welby 1961). At Mount Philo, 
for exaunple , the rocks of the upper plate are folded gently into 
an east-plunging syncline. Between Burlington and Snake Moun- 
tain the thrust is cut by a number of cross-faults that are in- 
terpreted as normal faults by Welby (1961, p. 204) . Our work 
indicates that the displacement on some of these faults is pre- 
dominantly strike slip (Stanley 1969, Sarkisian 1970). 

The stratigraphic throw on the Champlain thrust is in the 
order of 8000 feet at Burlington. To the north the throw de- 
creases as the Champlain thrust is lost in the shale terrain 
north of Rosenberg, Canada. Part, if not all, of this displace- 
ment is taken up by the Highgate Springs and Philipsburg thrust 
which continues northward and becomes the "Logan's Line Thrust" 
(Cady 1969) . South of Burlington the stratigraphic throw is 
in the order of 5500 feet. As the throw decreases on the Cheun- 
plain thrust near Cornwall the displacement is again taken up 
in part by the Orwell, Shoreham, and Pinnacle thrusts, which 
place Upper Cambrian and Lower Ordovician rocks on each other 
and eventually on the Middle Ordovician rocks to the west (Cady 
1945) . 



119 



The configuration of the Champlain thrust at depth is 
speculation. Where it is exposed the thrust surface is essen- 
tially parallel to the gently-dipping beds in the upper plate. 
This thrust geometry persists for at least 2-3 miles east of 
its most western limit since the thrust is still essentially 
parallel to the bedding in the Nonkton Quartzite at the base 
of the upper plate in the center of the recess of the thrust 
trace on the Monkton culmination. Further to the east the 
thrust must eventually steepen in dip and pass into Precaunbrian 
basement since it does not reappear at the surface on the west 
side of the Precambrian core of the Green Mountains. This over- 
all configuration is shown in the cross sections accompanying 
the geologic map of Vermont (Doll and others 1961) . 

The age of the Champlain thrust is debatable. Cady (1969, 
p. 75) believes the thrust developed in the Acadian Orogeny al- 
though the youngest rocks exposed below the Chzunplain thrust are 
Middle Ordovician in age. Welby (1961, p. 221) believes the 
thrust developed during the Taconic orogeny of Middle to Upper 
Ordovician age. Thrusting predates the emplacement of the Meso- 
zoic dikes which clearly cut the structures of the Champlain 
thrust. 

Our work shows that the Champlain thrust has undergone an 
extensive structural history involving possibly more than one 
period of thrusting. Perhaps the most compelling evidence for 
a multiple history of displacement is the presence of prograde 
chlorite in recrystallized fractures in the Monkton on the upper 
plate and the absence of prograde chlorite throughout the pelitic 
rocks directly below the thrust. We tentatively suggest that the 
Champlain thrust was originally developed during the Taconic oro- 
geny, metaunorphosed and then reactivated to place a metamorphosed 
upper plate on an unmetamorphosed lower plate. Although the sec- 
ond event may also be Taconic in age, since rocks of Silurian and 
Devonian age arembt present below the thrust, the additional 
structural events may have occurred during the Acadian orogeny. 
These speculations will be discussed during the trip. 

STRATIGRAPHY 

A composite stratigraphic section and correlation chart 
for the area of the Champlain thrust and the Hinesburg synclin- 
orium are shown in Table 1 and Table 2 respectively. 



120 



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STOP DESCRIPTIONS 

General 

The trip consists of five stops along the Champlain thrust. 
These stops are located on figure 1. 

Stop 1 . Lone Rock Point, Burlington (1, 2a, 2b, figure 2) - This 
locality is perhaps one of the finest exposures of the Champlain 
thrust in Vermont and Canada. Here the Dunham Dolomite (Conners 
facies) of Lower Cambrian age overlies the Iberville Formation 
of Middle Ordovician age. The thrust contact is sharp and mark- 
ed by a thin zone of breccia in which angular clasts of dolo- 
stone are endsedded in a highly contorted matrix of shale. Sliv- 
ers, several feet thick, of limestone are found along the fault 
and may represent pieces of the Beekmantown Group (Beldens Mem- 
ber of the Chipman Formation ?). The undersurface of the Dunham 
Dolomite along the thrust is grooved by fault mullions which 
plunge 15* to the southeast (figure 2, diagreun 1 and 2a) . The 
average southeastward dip of the thrust is 10 degrees. 

A variety of minor structures are found in the Iberville 
Formation whereas fractures are the only structures in the Dun- 
ham Dolomite. Many of these faults are filled with calcite and 
grooved with slickensides. The minor folds in the shale are num- 
erous, amd are easily grouped into two ages. The early folds 
have a well developed slaty cleavage that forms the dominant lay- 
ering in the Iberville and is concordant to the thrust surface at 
the base of the Dunham Dolomite. 

The younger generation consists of asymmetrical drag folds 
with short, gently curved hinges and rather open concentric pro- 
files. The axial surface is rarely marked by cleavage but when 
it is developed, fracture cleavage, filled with calcite, is typi- 
cal. These folds deform the slaty cleavage of the older gener- 
ation and are related to movement of the Champlain thrust since 
they decrease in abundance away from the thrust surface. The 
orientation of 59 axes with their sense of rotation is shown in 
diagrams 1, 2a, and 2b of figure 2. 

Slip line orientations . Drag folds of the younger generation 
have been used at 5 localities to determine a direction of move- 
ment on the Champlain thrust. Two of these localities are in 
the Iberville or Stony Point Formations directly below the thrust 
and 2 localities are in the Monkton Quartzite just above the 
thrust (diagrams 1, 2a, 2b, 3, 7, 8, figure 2). The remaining 
locality at Shelburne Point is along a fault zone in the Stony 
Point Formation less than a mile west of the Champlain thrust. 
At each of these localities numerous younger folds are developed 
with nonparallel hinges and short limbs facing in a variety of 
directions. 



123 



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125 



A slip line or movement direction was determined at three 
stations along the 2000 feet of exposure at Rock Point (diagram 
1, 2a, 2b, figure 2) using the methods described by Hansen (1967, 
1971) . The hinge orientation and sense of rotation for 18 to 23 
younger folds were plotted at each station on a lower hemisphere 
equal area net. The great circle that best approximates the spa- 
tial distribution of axes defines the slip plane which is approx- 
imately parallel to the older cleavage and the Champlain thrust. 
At Rock Point this cleavage is of compact shale separated by 
thinner layers of extremely fissile shale. In all the diagrams 
in figure 2 clockwise or dextral folds occupy one part of the 
great circle, whereas counterclockwise or sinistral folds occu- 
py the other. The arc that separates the opposite senses of rot- 
ation contains the slip direction. This is uniquely defined when 
the separation arc is zero. In most localities the separation 
arc is greater than zero and the bisector of the separation arc 
is arbitrarily designated as the slip direction. The overall 
symmetry of the fabric is monoclinic with the plane of symmetry 
oriented parallel to the slip direction and perpendicular to the 
slip plane. 

The location of clockwise and counterclockwise arrows on 
either side of the separation arc indicates the direction of 
movement of the upper layers along the deduced slip line. In 
diagrams 2a and 2b (figure 2) the upper layers moved to the north- 
west approximately along a line striking N40W for 2a and N54W for 
2b. In contrast , the upper layers moved eastward along a line 
striking N86E for tne southern part of the Champlain thrust at 
Rock Point (diagram 1, figure 2), In all three diagrams the sep- 
aration arc ranges in size from 5 to 12 degrees. 

Discussion of Results . The kinematic basis for drag fold analy- 
sis has been worked out in such geologic environments as tundra 
and sod slides, glacial lake clays, lava flows, and metamorphic 
rocks of all grades (Hansen 1967, Hansen and others 1967, How- 
ard 1968, Hansen 1971). Scott (1969, p. 251-254) has verified 
these methods in the laboratory using substances of different 
viscosities. In all these studies it has been shown that the 
separation arc contains the slip line and that the drag folds are 
a product of one overall movement regimen. 

As shown in diagram 11 of figure 2, the deduced slip lines 
are nearly parallel along 25 miles of the Champlain thrust. 
These slip directions are essentially parallel to fault mullions 
on the thrust surface at Lone Rock Point and slickensides on cal- 
cite-veneered surfaces at Shelburne Point (diagram 3) and else- 
where in the Middle Ordovician shale of the lower plate (Hawley 
1957, p. 81). Although the origin of the diversity in hinge ori- 
entation in the rocks along the Champlain thrust is still unclear, 
the approximate parallelism among slickensides, mullions, and 



126 



slip lines indicates that the slip lines deduced from drag folds 
are a reliable movement indicator. 

A generalized principal plane of stress and strain can be 
determined from slip line and plane information if rotation a- 
bout the pole to the slip plane is assumed to be zero. With this 
restriction the slip line and the poie to the slip plane define 
the plane of Oj and a, and Xj emd A,.*-' This plane, known as the 
deformation plane, is also the plane of monoclinic symmetry of 
the drag fold diagrams. The location of Cj in the deformation 
plane depends on the sense of shear across the slip surface, the 
coefficient of internal friction of dolostone on shale and the 
strong planar anisotropy along the Champlain thrust. 

The anomalous easterly slip direction for the southern 
part of Lone Rock Point (diagram 1, figure 2) will be discussed 
during the trip. 

Stop 2 . Shelburne Access Area (S14, figure 1) - The fractures 
and faults at this locality are ideal for dynamic analysis. The 
outcrop is located in the upper member of the Monkton Quartzite 
approximately 900 feet above the Champlain thrust. A high angle 
cross fault offsets the thrust just to the northwest (figure 1) . 

The location, orientation and relative displacement on 
faults and feather fractures are shown on the geologic map (fig- 
ure 3). At each numbered station the orientations, relative a- 
bundance and surface features of 10 fractures were measured. 
Diagram A of figure 4 shows the poles to 248 fractures and dia- 
gram B shows four planes corresponding to the maxima in diagram 
A. The trend and deduced sense of displacement of the feather 
fractures are shown in diagram D of figure 5. 

The faults in figure 3 are generally vertical, contain a 
very narrow zone of gouge and are divided into an east-west 
group and a north-south group according to their general strike. 
The north-south group are few in number and displace the east- 
west faults and hence, are younger in age. The faults of both 
generations are wrench faults since the dip slip displacement is 
only several inches and the strike slip displacement is as large 
as 3 feet. Furthermore, feather fractures adjacent to many of 
the faults are only present on the horizontal surfaces. Petro- 
fabric analysis of quartz deformation lamellae in samples Ml, 
M3, M4 (figure 4) further supports this conclusion (figure 6) . 

'oi, ffj , Oi refer to the principal axes of stress with <^ re- 
presenting the maximum compressive stress. XwXj , X3 are the 
principal directions of quadratic elongation with Xj represent- 
ing the direction of maximum elongation. 



127 




EXPLANATION 



Qs 



Surticial Deposits 



MAJOR UNCONFORMITY 



\s^ 



Monkton Ouartzite 



STRUCTURAL SYMBOLS 

X Strike and dip of bedding 

5s^86 Faults, showing trend, dip and apoarent 

nnovennent Dashed where in doubt or 
^ covered 



X 



Feather array. Barbed long line indicates 
trend of array Short line indicates trend 
of individual fracture. 

Specific faults 



• Station location for fracture data 

<D Oriented sannple location. 



GEOLOGIC MAP 
OF 
SHELBURNE ACCESS AREA 

by 
Stanley and Chase 1971 

10 O 10 20 30 Fffft 



D 



SCALE 
Lake Level 978' 



Figure 3. Structures in the Monkton Quartzite at the southern 
end of Shelburne Bay, western Vermont. Located at station S14 on 
figure 1. 



128 








^ / 



each of the faul?s in H^. ^^^^^^P^^^^^^ ^^"^^^ °f shear for 

stresses deduced for the lecond* °'^^^^" ° ^^°"" ^^^ principal 
wrench faults Their ^^LJ!^ generation of complimentary 

shear are indicate? L"rsoridlo?''^H'^"^''°"" ^"^ ^^"^^^ °f 
gram E shows the trend and i^f.? J^ concentric arrows. Dia- 
21 feather-fracture arrays ^^^^"^"^^ displacement deduced from 



129 





Figure 4. Lower hemisphere equal area projections of macroscopic 
fractures in the Monkton Quartzite at the Shelburne Access area. 
Diagram A shows 248 poles to fractures. Contour intervals are 
0.4, 1.2, 2.0, 2.8, 3.6 respectively per 1 percent area. Diagram 
B shows planes corresponding to the 3.6 oorcent maxima of diagram 
A. 




B 



Figure 6. Synoptic diagram of the principal stress positions 
deduced for generation one and two wrench faults, megascopic 
fractures, feather fracture arrays and quartz deformation lam- 
ellae at Shelburne Access area. 



130 



The dihedral angle between complementary wrench faults 
(for ex2ut\ple, e, p, i figure 3) ranges from 15 to 70 degrees 
with an average of 27 degrees which implies either a high val- 
ue for the angle of internal friction, or fracturing under low 
effective confining pressures (less than 500 bars perhaps) . 
These conditions were probably near the earth's surface since 
the pressure effect of a pore fluid was minimal after low grade 
me t amo r ph ism. 

Microscopic planes of hematite inclusions, recrystallized 
quartz veins, unfilled fractures, quartz deformation lamellae, 
and undulose extinction in quartz pervade all thin sections. 
Prograde chlorite occurs between grains and along recrystallized 
quartz veins. Thus, the early sets of fractures were metamor- 
phosed at the chlorite grade forming the recrystallized quartz 
veins and planes of inclusions. The unfilled fractures and 
quartz deformation lamellae were then superposed on and influ- 
enced by this annealed fabric. 

Dynamic Analysis . Fractures, faults and quartz deformation pro- 
vide information on the orientation and relative magnitudes of 
the principal stresses. 

1) Fractures: Dynamic interpretation of fractures is based on 
geometry and the identification of shear or extension fractures. 
The intersection of the 4 fracture sets in diagram B (figure 4) 
defines the aa position. The Oi direction is oriented 90 degrees 
to 2 in the plane that bisects the acute angle between shear 
fractures. The acute angles between fracture sets 1 and 3 and 2 
and 4 are 80 and 83 degrees respectively. Set 1 fractures are 

in the extension position because they parallel the fractures in 
the feather arrays. Fracture sets 2 and 4 are, therefore, shear 
fractures and oi plunges eastward at 10 degrees in the plane of 
fracture set 1. oj trends northward and corresponds to the 
pole of fracture set 1. The deduced principal stresses are 
compatible with the stress configuration indicated by the wrench 
faults of generation 1. 

2) Feather fractures? The feather arrays in diagram D (figure 5) 
with their respective senses of shear indicate that d is orien- 
ted east-west, o, trends north-south and aj is vertical. The 
principal stresses deduced for fractures and feather arrays agree 
in trend but differ by 10 degrees in dip since only the trend can 
be measured and not the dip of feather arrays. 

3) Wrench faults of generation 1: Diagram A in figure 5 shows the 
deduced positions for the principal stresses calculated for 
faults labelled a through g on figure 3. These calculations were 
based on complementary faults (e,o,p,q) and faults with their 
associated feather fractures (c,d,g,h,i, j ,k) . The principal 



131 



stress positions are contoured in diagram C of figure 5 which 
shows that oi plunges gently eastward, 3 trends northward, 
and O2 is nearly vertical. Diagraun B (figure 5) shows that 
right lateral faults trend northeasterly whereas left lateral 
faults trend northwesterly. 

4) Wrench faults of generation 2: The deduced positions for the 
principal stresses calculated from complementary faults (I, III, 
and IV, figure 3) and offset structures cut by fault II (figure 
3) are shown in diagram E of figure 5. A comparison of diagrams 
C and E of figure 5 indicates that Oj for fault generations 1 
and 2 are parallel. The positions of Oi and 03 however are in- 
terchanged. This orthogonal relationshio implies that the sec- 
ond generation may have been caused by displacements associated 
with the first generation. As movement occurred during genera- 
tion 1 the east-west stresses were reduced to a minimum value 
and the north-south stresses were simultaneously increased to 
the maximum compressive value. The stage was then set for gen- 
eration 2 faulting. 

5) Deformation lamellae in quartz: The lamellae are similar in 
character to those described by Carter and others (1964) . The 
results were analyzed using methods described by Carter and Fried- 
man (1965), and Scott and others (1965). The deduced orienta- 
tion for oi, 02 , and ai are shown in figure 6. In M3 and M4 , 

a I lies in the bedding and az appears to be equal to o 3 in magni- 
tude. In Ml, 01 is inclined 40 degrees to the east, 02 dips 50 
degrees to the west and as trends northward and is horizontal. 
Although these orientations are not parallel in all samples, they 
are consistent with the stress positions deduced from the frac- 
tures, feather fractures, and first generation faults. The stress 
configuration in Ml is triaxial with a i>a 2>a 3 whereas the config- 
uration in samples M3 and M4 is biaxial with oi>a2 » 03. These 
patterns indicate that the quartz Icimellae formed during and 
slightly after the wrench faults of generation 1. 

Relationship to major faults . Wrench faults are commonly assoc- 
iated with thrust faults. Both can be related to the same Oi 
direction and only require a switch of 02 and oj in the stress 
configuration during thrusting to develop wrench faults. The 
small wrench faults in the Monkton Quartzite bear the same rela- 
tionship to the Champlain thrust and as such, suggest that some 
cross faults shown on the Geologic Mao of Vermont (Doll, and 
others, 1961) are indeed wrench faults. 

One of these cross faults was mapped by Welby (1961) just 
to the northwest of the Shelburne Access Area (figure 1). It 
strikes northeasterly and displaces the upper and lower plates 
of the Champlain thrust in a right lateral direction. Because 
the deduced sense of Oi for first generation faults and assoc- 



132 



iated structures dip eastward more gently than the Champlain 
thrust (approximately 10 degrees) the inferred horizontal dis- 
placement on the cross fault would result in the same apparent 
vertical movement as indicated on the map (figure 1) . This 
movement geometry also characterizes the right lateral faults 
of generation 1 at Shelburne Access Area. The cross fault of 
the west side of Shelburne Bay and the first generation faults 
and their associated structures are considered to be coeval, 
and therefore, younger than the Champlain thrust since the maj- '| 

or cross fault clearly cuts both the plates of the thrust. i 

'i 

S tructural History . The structural history for this outcrop j 

and nearby major faults is summarized in figure 7. 

S top 3 . Location S9 - Route 7 a mile north of Shelburne (S9, 
figure 1) - As shown on figure 8 the V-Jinooski Dolomite is down- 
thrown against the Monkton Quartzite along a normal fault trend- 
ing slightly north of east. Eight smaller normal faults of sim- 
ilar trend cut parts of the Winooski (one is in the Monkton) . 
Three small faults trend east of north and may be related to a 
larger fault which offsets the fault between the Monkton and the 
Winooski. This fault was apparently excavated when Route 7 was 
constructed. Several of the northeasterly-trending faults have 
well defined gouge zones ranging in thickness from less than an 
inch to slightly more than a foot. The most obvious zone is a- 
long the fault between the two formations. Well developed slic- 
kensides indicate a dominant dip slip component for all displace- 
ments (figure 9) . A second nearly horizontal slickenside is pre- 
sent on the fault directly north of station 19 in the Monkton 
Quartzite on the east side of Route 7. 

Dynamic interpretation . The synoptic diagram in figure 9 shows 
the orientation of the faults and associated slickensides . 
These normal faults indicate a state of stress in which Oj would 
be horizontal and trend northwesterly, Oi would parallel the gen- 
eral strike of the faults, and ai would plunge to the southwest 
almost vertically. Inasmuch as the north-northeasterly faults 
cut the east-northeasterly faults the principal axes of stress 
probably rotated counterclockwise during this second event. 

Thirty-seven quartz deformation lamellae were measured in 
150 grains from the west side of the outcrop in the Monkton 
Quartzite (station S9, figure 8). The deduced positions are very 
similar to the stress positions deduced for the deformation lamel- 
lae at Shelburne Access Area, and hence the two are considered 
coeval (compare figures 6 and 9). The lamellae at S9 are thought 
to be older than the normal faults since horizontal slickensides 
indicating strike slip displacement are not present. If these 
faults were genetically related to the deformation lamellae then 
all but one should show right lateral displacement. According 
to figure 1 the Monkton-Winooski contact should be offset in a 



133 



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EXPLANATION 


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Surficial Deposits 






MAJOK UNCONf-tjKM- T T 


2 
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Winooski Dolomite 


5 
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Monkton Quartzite 


STRUCTURAL SYMBOLS 


\ 


Strike and dip of bedding 






yao Faults, showing trend, dip 

^ and apparent movement 

Querried where doubtful 

Station location for structure 
data 

« Oriented sample location 



GEOLOGIC MAP 

Of 
LOCATION S9 



10 



?0 



SCALE 



Figure 8. Geologic map of the normal faults at S9 just north 
of Shelburne, Vermont. 




Figure 9. Lower hemisphere equal area orojection showing the 
normal faults and associated slickensides at S9. The principal 
stress positions (1,2,3) deduced from quartz deformation lamel- 
lae in the Monkton Quartzite west of Route 7 are represented by 
solid dots. The generalized bedding at locality S9 (see figure 
8) is shown by the great circle labelled S. 



I 



135 



left lateral sense due to movement on the normal faults at this 
stop ( figure 8) . 

In summary the structural chronology at S9 begins with the 
quartz lamellae which developed as a result of east-west compres- 
sion associated with the gen'iration 1 wrench faults at Shelburne 
Bay. Northwest-southeast extension then produced the normal 
faults which dominate the outcrop. This stress configuration is 
reflected in quartz lamellae from an outcrop 2 miles to the south 
of S9. 

Stop 4 . Pease Mountai n near C harlotte (8, 10, figure 1) - The 
Champlain thrust and associated minor thrusts in its lower plate 
are well exposed on Pease Mountain (figure 10). The area was 
mapped by Cady (1945) and later remapped in greater detail by 
Welby (1961) and discovered outcrops of Bridport Dolomite on the 
western peak of the mountain. The area was mapped in still 
greater detail by students in field geology at the University of 
Vermont in 1969 and 1970. Our work has shown that the Bridport 
consists of two thrust slivers that have been subsequently de- 
formed so that the bounding thrusts are systematically folded. 

Stratigraphy: The abbreviated section at Pease Mountain includes 
part of the lower and upper members of the Monkton Quartzite 
which forms the upper plate of the Champlain thrust underlying 
the top and eastern slopes of the mountain. The Monkton is 
thrust on an overturned Middle Ordovician section that includes 
the upper part of the Glen Falls Formation, the Stony Point For- 
mation, and the Iberville Shale. Slivers of Bridport Dolomite, 
a member of the Chipman Formation of Lower Ordovician age, are 
mapped along the western peak of the mountain. A few primary 
structures in the Bridport show that it is generally right side up. 

Structure: Although thrusts dominate the structure on Pease Moun- 
tain, cleavage, folds and high angle faults are important aspects 
of the area. 

Cleavage dips gently to the east in the shaly rocks of the 
Monkton Quartzite, the Bridport Dolomite, and the shales of mid- 
dle Ordovician age. In the Monkton Quartzite the cleavage dips 
more steeply than the bedding which is a common relationship a- 
long the Champlain thrust (diagram A, figure 12) . 

Asymmetrical folds that deform the cleavage are restricted 
to the lower member of the Monkton Quartzite near the Champlain 
thrust. Six of these folds define a 65 degree separation arc 
with a deduced slip line that indicates movement of the upper 
plate in a N75W direction (diagram B, figure 12) . 

In the Iberville Formation on the east side of Route 7 
(figure 10) two generations of folds are well developed and are 



136 



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PEASE MOUNTAIN 

Profile Section 



500 



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Scalel ■■^ 



Figure 11. Modified profile section of Pease Mountain along a 
line of section labelled 1-2 on figure 10. No vertical or hori- 
zontal exaggeration. Displacement arrows only represent a com- 
ponent of the true direction of movement which is indicated by 
the slip direction deduced from the drag fold data shown in 
figure 10 and diagram B of figure 12. 



138 







Figure 12. Lower hemisphere equal area projections of selected 
structures on Pease Mountain. Diagram A shows poles to bedding 
and cleavage in the Monkton Quartzite. The intersection of bed- 
ding and cleavage and their anticlinal sense are represented by 
a solid dot with a concentric arrow. Diagram B shows the orien- 
tation of six drag folds which deform cleavage in the lower mem- 
ber of the Monkton Quartzite directly above the Champlain thrust 
north of point A on figure 11. Diagram C shows the orientation 
of generation one and two folds and the thrust fault in the Iber- 
ville Formation just east of Route 7 on figure 11. Diagrams D 
and E represent poles to bedding in the Bridport Dolomite. 
Dashed great circle represents the great circle that best approx- 
imates the distribution of poles. Diagram D contains 32 poles 
and diagram E contains 22 poles. 



139 



similar to the folds in the Stony Point Formation directly be- 
low the Champlain thrust at Lone Rock Point. At Pease ^tountain 
the older folds are far more abundant than the younger folds 
which are only developed below a fairly continuous thrust at the 
south end of the outcrop. The orientation of each of these gen- 
erations and the thrust is shown in diagram C of figure 12. The 
senses of rotation of the folds in both generations indicate 
movement to the northwest of upper beds over lower beds with a 
more northerly direction for the older set of folds. 

The Champlain thrust is exposed at two localities (A and 
B, figure 10) where the lower member of the Monkton overlies 
highly deformed shaly limestones of the Glens Falls Formation. 
Silicified minor faults are common in the Monkton just above the 
thrust and suggest an earlier deformation perhaps associated with 
early movements on the Champlain thrust. 

The Bridport slivers: The stratigraphic gap between the Bridport 
Dolomite and the surrounding Stony Point Formation leaves little 
doubt that the Bridport is bound by thrusts on the western part 
of Pease Mountain. Although the actual thrust surfaces are cov- 
ered the systematic change in orientation of bedding in the dol- 
ostones and limestone of the Bridport near the thrust throughout 
the sliver and in the limestone and shale at the southern end 
below the thrust indicates that the bounding thrusts are system- 
atically folded which is best seen around the southern end of 
the larger sliver. Poles to bedding in the Bridport define two 
diffuse great circles whose it pole ( 6 point) plunges S36E at 
25 degrees for the northern part and N4bE at 25 degrees for the 
southern part (diagrams D and E, figure 12). Since there is no 
evidence supporting superposition of one of these folds on the 
other, it is concluded that the fold axis in the Bridport sliver 
curves through 80 degrees from the southern end of the sliver to 
the northern end. 

The folded shape of the Bridport sliver indicates that it 
was systematically deformed after it was emplaced. It is sug- 
gested that the sliver was formed during the early stages of 
movement on the Champlain thrust and then was folded during sub- 
sequent movement on the thrust. 

Stop 5 . Mount Philo near Ferrisburg (7, figure 1) - Mount Philo 
is located along the Champlain thrust on the north limb of the 
Monkton culmination (Cady, 1945; Doll, and others, 1961) just 
south of Charlotte, Vermont (figure 1). Although the Champlain 
thrust is not exposed in this area, numerous east-west faults, 
folds, and several thrusts are well developed in the Monkton 
Quartzite which forms the upper plate of the thrust. Five ori- 
ented specimens of quartz deformation lamellae were analyzed by 
Sarkisian (1970) from three separate localities (Sll, S2, SF) 
located in figure 13. 



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Megascopic Structures: Bedding, slaty cleavage, asymmetrical 
concentric folds, fractures, and faults are well displayed a- 
long the southern and western cliff of Mount Philo (figure 13). 
Crossbedding and ripple marks indicate that the Monkton Quart- 
zite is right-side-up throughout the area. Cleavage is well 
developed in the thin shaly beds of the Monkton and dips east- 
ward more steeply than the VcJding where it is not folded. 
Large asymmetrical folds in the southern and western cliffs de- 
form the cleavage and plunge at very gentle angles in various 
directions. The sense of rotation of 12 of these folds on the 
upper plate of the Mount Philo thrust locate a horizontal slip 
line that trends N55W and indicates movement of the upper beds 
northwestward (figure 14). Four fairly large folds are also 
present directly below the Mount Philo thrust and indicate a 
slip direction slightly south of east. On the western cliff 
of Mount Philo below the thrust high angle faults commonly dip 
northward and southward. Although movement on the surfaces 
are commonly normal, movement in the reverse sense was noted. 
In two key areas north-dipping faults high on the cliff flatten 
at a lower elevation and pass into high angle south-dipping 
faults further on and up the cliff. These fault surfaces, there- 
fore, form U-shaped channels and show either normal or reverse 
movements across the fault surface. The Mount Philo thrust cut 
these high angle faults and hence is younger in age. 

The Mount Philo thrust crops out for at least 700 feet 
along the southern and western cliffs of Mount Philo (figure 13). 
It is a sharp, undeformed surface that dips gently eastward and 
truncates the asymmetrical folds within the lower portion of the 
Monkton Quart zite. 

Several fracture sets are well developed on Mount Philo. 
They cut the folds, high angle faults, and the Mount Philo thrust. 
At locality S2 (figure 15) Sarkisian measured 163 fractures a- 
cross one of the asymmetrical folds. The resulting fabric (fig- 
ure 15) shows three statistical fracture sets which correspond 
to the maxima in the contoured equal area diagram. This fabric 
is undeformed by the fold since separate plots on opposite limbs 
of the fold are similar to the diagram in figure 15. The plane 
of symmetry bisecting fractures 1 and 3 is perpendicular to 
fracture 2 and is approximately parallel to the slip line deter- 
mined from the asymmetrical folds. 

Microscopic Structures: Five oriented samples of Monkton Quart- 
zite were collected from three separate localities on the west- 
ern side of Mount Philo (Sll, S2, SF, figure 13). One sample 
(Sll) was collected below one of the east-west faults, another 
(S2) comes from the locality where 163 fractures of figure 15 
were analyzed and the remaining three (SIO, S12, S13 at locality 
SF) were collected from the limbs and hinges of an asymmetrical 



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drag fold. Oriented samples were, therefore, selected from 
all of the megascopic structures except the Mount Philo thrust. 

For each sample 75 (50 for Sll) quartz grains were stud- 
ied from each of three mutually perpendicular thin sections. 
The quartz lamellae are similar to those described for the Shel- 
burne Access Area and locality S9. 

Synoptic diagram A in figure 16 shows the principal stress 
positions deduced from deformation lamellae on Mount Philo. For 
all the samples the poles to lamellae define small circle girdles 
with radii that range from 55 to 64 degrees. This pattern cor- 
responds to a cone of lamellae oriented less than 45 degrees to 
the central cone axis, Oi . The principal stress directions de- 
duced from the five specimens are remarkably constant in orien- 
tation and configuration. The Oi directions fall in a narrow 
30 degree arc oriented north of west (average direction, N75W) . 
The 02 and Oj directions are approximately equal in value and 
hence, define the plane perpendicular to a i . The trend of Oi 
is approximately 20 degrees counterclockwise to the trend of 
the slip direction (N55W) deduced from the asymmetrical drag 
folds (figure 16) . 

Since the quartz fabric axes have not been rotated by the 
folds at SF, the quartz deformation lamellae were superposed on 
this fold after it had fully developed. East-west fractures in 
sample Sll collected near the high-angle faults offset the de- 
formation lamellae and suggest that the lamellae are older than 
the Mount Philo thrust and its associated channel faults. 

Relationship of Quartz Deformation Lamellae to the Megascopic 
Structures: The quartz deformation lamellae on Mount Philo have 
resulted from a nearly horizontal maximum compressive stress 
generally oriented in N75W direction. The values of a^ and Oj 
were approximately equal during lamellae development. The quartz 
lamellae reflect a stress configuration that is compatible with 
the north-trending Champlain thrust. It is also similar to the 
stress configurations deduced from samples M3 and M4 at Shelburne 
Access Area which are in turn correlated with the first genera- 
tion wrench faults and the Shelburne Bay cross fault. Thus the 
lamellae at Mount Philo probably developed with the younger 
wrench faults which cut the Champlain thrust. 

At Mount Philo the deformation lamellae are younger than 
the asymmetrical drag folds since the lamellae fabric axes re- 
main constant in orientation across the fold. In sample Sll 
small shear fractures offset quartz deformation lamellae. These 
fractures parallel the east-west channel fault and hence are con- 
sidered younger than the deformation lamellae. This temporal 
relationship would further support the conclusion that the high 



1^^ 




Figure 16. Synoptic diagram of principal stress positions de- 
duced from quartz deformation lamellae (S2, SIO, Sll, S12, S13) 
and fractures. The numbers 1^, 2_, 3_ correspond to the principal 
compressive stresses with 1^ representing the direction of maxi- 
mum compressive stress. Alternative principal stress positions 
for fractures are represented by primed and unprimed numbers. 
The slip line deduced from the drag folds in figure 14 is also 
included in the projection. 



145 



angle faults and the Mount Philo thrust are younger than the 
asynunetrical folds. 

In summary the structural sequence at Mount Philo begins 
with the development of cleavage and is followed by the folding 
of the Monkton into west-facing folds possibly as a result of 
movement of the Champlain thrust to the northwest. Subsequent 
deformation produced the quartz deformation lamellae which are 
thought to be coeval with the first generation of wrench faults 
at Shelburne Bay. Continued west northwest - east southeast 
compression resulted in the channel faults and the Mount Philo 
thrust. Fracturing subsequently developed and may reflect a 
change in orientation of the principal stresses although the 
fracture can be related to the previous stress configuration. 

S ummary of structural chronology . The temporal relationship a- 
mong the structures at the five localities along the Champlain 
thrust are summarized in figure 17. Reasons supporting their 
age assignments are discussed at each locality and will not be 
repeated here. The following comments will be restricted to the 
relationship of these structures to such major structures or e- 
vents as the Champlain thrust, Hinesburg synclinorium, Hinesburg 
thrust, and the various orogenies known in the Appalachians. 

As shown in figure 17. and emphasized at different locali- 
ties, the Chaunplain thrust is thought to have undergone a multi- 
ple history beginning with initial emplacement during the Tacon- 
ic orogeny and ending with renewed movement in a subsequent oro- 
geny, proba±>ly the Acadian of Middle Devonian age. Since the 
youngest rocks below the Champlain thrust are Middle Ordovician 
in age it seems unjustified to restrict its development to the 
Acadian orogeny as suggested by Cady (1969, p. 75). Subsequent 
movement apparently did occur during the Acadian or possibly the 
Allegheny orogeny since the chlorite-qrade rocks of the upper 
plate now rest on essentially unmetamorphosed rocks of the lower 
plate. Radiometric work in thenorthern Taconics (Harper, 1968), 
along the Sutton-Green Mountain anticlinorium (Cady, 1969, p.l04)f 
and in Quebec (Rickard, 1965) indicate that recrystallization in 
northwestern Vermont was older than 400 m.y. and hence of Tacon- 
ic age. Petrologic work by Albee (1968) lends further support 
to this conclusion. Thus renewed movement on the Champlain 
thrust is restricted to post Taconic activity. 

Based on the foregoing conclusions the second generation 
of younger folds in the lower plate, the asymmetrical folds 
which deform cleavage in the upper plate, and the deformation of 
the Bridport sliver on Pease Mountain are contemporaneous with 
renewed activity on the Champlain thrust. The older generation 
of folds in the lower plate, the original emplacement of the 
Bridport sliver, the formation of cleavage in the Monkton, and 
low grade metamorphism may well be associated with, or just after. 



146 



Paleozoic 



Taconic 
Orogeny 



Acadian Orogeny 
or 
(Allegheny Orogeny) 



2 
a 

M 

o 

N 
O 

o 



t-. Champlain Thrust 

"U 3 

o It Older folds 




7 
/ 
/ 
/ 
/ 
/ 
/ 
/ 
/ 
/ 
/ 
/ 

/ 
/ 
/ 
/ 

/ 
/ 
/ 






" Younger folds 







> Shelburne Bay 

w crossfault 

n i» Wrench faults 1 
S o^ Wrench faults 2 
^ c Fractures emd 
U 3 feather fractures 

01 " Quartz deformation 

lamellae 


W JO 

nc Normal faults ENE 
^^ Normal faults NNE 
c Quartz deformation 
S ^ lamellae 

Cleavage Monkton Qtzite. 


^ -^ Folds Monkton Qtzite. 
§ 2 Foldt Iberville Fm. 






nv Thrusts Bridport Dol. 

£1. " Folding of thrusts 

^ around Bridport Dol. 

Cross faults 

Fractures 









Cleavage Monkton Qtzite. 


^^ Folds Monkton Qtzite. 
^. g Mt. Philo thrust 
^3 Channel faults 
° '* Fractures 

Quartz deformation 
lamellae 







Hinesburg Synclinorium 
1st generation folds 


2nd generation folds 




Hinesburg thrust 




Metiunorphism 
Uplift 

Lamprophyre fc Bostonite 
Intrusives 





Figure 17. Chronology of selected structural events in the 
Hinesburg synclinorium and along the Champlain thrust in the 
central part of western Vermont. 



1^7 



early development of the thrust. The two generations of wrench 
faults, the normal faults, and the quartz deformation lamellae 
are younger than the Champlain thrust and are probably Acadian 
in age although an Allegheny age is certainly possible. 

The structures in the Hinesburg synclinorium and along 
the Hinesburg thrust can be placed in this chronological se- 
quence although our work is still in progress (Gillespie and 
others, this guidebook). The rocks in the southern part of the 
synclinorium have been involved in at least two, and in some 
places, three generations of folds. The axes of the first gen- 
eration of tight folds plunges gently southeastward with a well- 
developed closely spaced cleavage. These folds are, in turn, 
folded into rather open folds with north plunging axes and steep 
eastward dipping' axial surfaces. The map pattern in the south- 
ern part of the Hinesburg synclinorium is actually a product of 
both of these fold events (figure 1, Doll and others, 1961). An- 
alysis of quartz lamellae in the Monkton at Mount Philo, S8 and 
farther east by Sarkisian and Marcotte indicate the lamellae are 
younger than the second generation of folds since the deduced 
stress positions are not deflected by the major folds. Thus the 
formation of the Hinesburg synclinorium predates the wrench 
faults and associated quartz deformation lamellae. Since there 
has been recrystallization of micaceous material in the axial 
surfaces of the first and possibly the second generation of 
folds, these events are probably Taconic. 

The Hinesburg thrust is clearly folded by the second gener- 
ation of folds in the synclinorium and therefore is also consid- 
ered to be Taconic in age. 

The lamprophyre and bostonite dikes that cut the Champlain 
thrust, the Hinesburg synclinorium and the upper plate of the 
Hinesburg thrust are the youngest structures recognized in west- 
central Vermont. These intrusives are Mesozoic in age since 
K-Ar measurements on biotite from the syenite stock at Barber 
Hill in Charlotte indicate an age of 111 + or - 2 m.y. (Arm- 
strong and Stump, 19 71) . Similar work on a lamprophyre from 
Grand Isle yield an age of 136 + or - 7 m.y. (Zartman and others, 
1967) . 



li^8 



REFERENCES CITED 

Albee, A. L., 1968, Metamorphic zones in northern Vermont, 
p. 329-341, iji: Zen, E-an, White, W. S., Hadley, J. J., 
and Thompson, J. B. , Jr., Editors, Studies of Appalachian 
Geology, Northern and Maritime: New York Interscience 
Publishers, John Wiley and Sons, Inc., 475 p. 

Armstrong, R. L. , and Stump, Edward, 1971, Additional K-Ar 
dates. White Mountain magma series. New England: Am. Jour. 
Sci., V. 270, p. 331-333. 

Cady, W. M. , 1945, Stratigraphy and structure of west-central 
Vermont: Geol. Soc. America Bull., v. 56, p. 515-587. 

, 1969, Regional tectonic synthesis of northwestern New 



England and adjacent Quebec: Geol. Soc. America Memoir 120,181p. 

Clark, T. H. , 1934, Structure and stratigraphy of southern 
Quebec: Geol. Soc. America Bull., v. 45, p. 1-20. 

Doll, C. G., Cady, W. M. , Thompson, J. B., Jr., and Billings, 
M. P., Compilers and Editors, 1961, Centennial Geologic Map 
of Vermont: Montpelier, Vermont, Vermont Geol. Survey, 
scale 1:250,000. 

Hansen, Edward, 1967, Methods of deducing slip-line orientations 
from the geometry of folds, iii: Carnegie Inst. Wash., Year- 
book 65, p. 387-405. 

, 1971, Strain facies: Springer-Verlag, New York, Inc., 

270 p. 

, Scott, W. H. , and Stanley, R. S., 1967, Reconnaissance 

oT slip-iine orientations in parts of three mountain chains, 
in: Carnegie Inst. Wash., Yearbook 65, p. 406-410. 

Harper, C. T., 1968, Isotopic ages from the Appalachians and 
their tectonic significance: Canadian Jour, of Earth Sci., 
V. 5, p. 50-59. 

Hawley, David, 1957, Ordovician shales and submarine slide brec- 
cias of northern Champlain Valley in Vermont: Geol. Soc. 
America Bull., v. 68, p. 155-194. 

Hitchcock, Edward, Hitchcock, Edward, Jr., Hager, A. D. , and 
Hitchcock, Charles, 1861, Report on the geology of Vermont, 
vol. 1, 558 p.; vol. 2, p. 559-988, Claremont, Vermont. 



149 



Howard, K. A., 1968, Flow direction in triclinic folded rocks: 
Am. Jour. Sci., v. 266, p. 758-765. 

Keith, Arthur, 1923, Outlines of Appalachian structure: Geol. 
Soc. America Bull., v. 34, p. 309-380. 

, 19 32, Stratigraphy an'.l structure of northwestern Vermont: 

Washington Acad. Sci. Jour., v. 22, p. 357-379, 393-406. 

Rickard, M. J., 1965, Taconic orogeny in the Western Appala- 
chians: Experimental application of microtextural studies to 
isotope dating: Geol. Soc. America Bull., v. 76, p. 523-536. 

Rodgers, John, 1968, The eastern edge of the North American con- 
tinent during the Cambrian and Early Ordovician, p. 141-149, 
in: Zen, E-an, et al . , 1968, Editors , Studies of Appalachian 
geology. Northern an3^ Maritime: New York Interscience Publish- 
ers, John Wiley and Sons, Inc., 475 p. 

Sarkisian, A. C. , 1970, A petrofabric analysis of the Monkton 
Quartzite in west-central Vermont: M. S. thesis. University 
of Vermont, Burlington, Vermont, 120 p. 

Scott, W. H., 1969, Experiments in flow deformation, in: Car- 
negie Inst. Wash., Yearbook 67, p. 251-254. 

Stanley, R. S., 1969, Bedrock geology of the southern portion 
of the Hinesburg synclinorium, in: Guidebook to field excur- 
sions of the New York State Geological Association, 41st 
Annual meeting, Plattsburg, New York, p. 37-64. 

Welby, C. W. , 1961, Bedrock geology of the Champlain Valley of 
Vermont: Vermont Geol. Survey Bull. 14, 296 p. 

Zartman, R. E. , Brock, M. R. , Heyl, A. V., and Thomas, H. H. , 
1967, K-Ar and Rb-Sr ages of some alkalic intrusive rocks 
from central and eastern United States: Am. Jour. Sci., 
V. 265, p. 848-870. 

Zen, E-an, 1967, Time and space relationships of the Taconic 
allochthon and autochthon: Geol. Soc. America Special Paoer 
97, 107 p. 

, 196 8, Nature of the Ordovician orogeny in the Taconic 



area, p. 129-139, in: Zen, E-an, et al^. , 1968, Editors , 
Studies of AppalacRTan geology, NortViern and Maritime: New 
York Interscience Publishers, John Wiley and Sons, Inc., 
475 p. 



151 



SEDIMENTARY CHARACTERISTICS AND TECTONIC 

DEFORMATION OF MIDDLE AND UPPER ORDOVICIAN 

SHALES OF NORTHWESTERN VERMONT NORTH OF 

MALLETTS BAY 



by 

David Hawley, Hamilton College , Clinton, New York 

Introduction 

The central lowland of the Champlain Valley is underlain by Cambrian 
and Ordovician sedimentary rocks, bordered on the west by the Adirondack 
Mountains of Precambrian crystalline rock upon which Cambrian sandstone 
lies unconformably , and against which sedimentary rocks have been dropped 
along normal faults. The lowland is bordered on the east by low-angle 
thrust faults on which massive dolomite, quartzite, and limestone, as old 
as Lower Cambrian, from the east over-rode weaker Ordovician shale and 
limestone. The westernmost thrusts, the Highgate Springs thrust in the 
north, and the overlapping Champlain thrust in the south, trace an 
irregular line a few feet to 3 1/2 miles inland from the east shore of Lake 
Champlain. For most of the distance between Burlington and the Canadian 
border, the high line of bluffs marking the trace of the Champlain Thrust are 
composed of the massive, Lower Cambrian Dunham dolomite. 

The shales, youngest rocks of the autochthonous lowland sequence, 
outcrop on most of the islands in Vermont, and the mainland between the 
thrusts and the 'ake. Although exposures on almost continuous shore-line 
bluffs are excellent, there are few outcrops inland because of glacial cover 
and low resistance of the shales to weathering. Fossils are rare in the 
older calcareous shale (Stony Point) and absent in the younger non- 
calcareous shale (Iberville). The lithic sequence was established almost 
entirely on structural criteria. Where it can be found, the Hathaway 
submarine slide breccia structurally overlies the Iberville. 

Description of Formations 

Glens Falls Limestone 

Kay (1937, p. 262-263) named the lower Glens Falls the Larrabee member, 
found it to be 72 feet thick on the Lake Champlain shore in the north- 
western part of South Hero Township, Vermont, and to be composed there of 



152 



thin-bedded, somewhat shaly limestone. Fisher (1968, p. 27) has found 
the Larrabee member to be 20 to 30 feet thick in the vicinity of Chazy, N. Y. , 
and to be coarse-grained, medium- to thick-bedded light gray limestone full 
of fossil debris (brachiopods , crinoids, pelecypods, and trilobites). 

The upper Glens Falls was named the Shoreham member by Kay (1937, 
p. 264-265), and described as the zone of Crvptolithus tesselatus Green, a 
distinctive trilobite. He found 30 feet of the Shoreham exposed in the 
lakeshore in northwestern South Hero Township. Fisher (1968, p. 28) prefers 
to call this the Montreal limestone member, following Clark's usage for the 
Montreal area (1952), and has described it as medium dark gray to dark gray 
argillaceous limestone with shale partings, fossiliferous with trilobites, 
brachiopods, molluscs, and bryozoa. He estimates it to be 150-200 feet 
thick in Clinton County, N.Y. 

Cumberland Head Formation 

The "Cumberland head shales" was a term used, but not carefully 
defined by Gushing (1905, p. 375), referring to the interbedded shale and 
limestone forming a gradation between the Glens Falls and the overlying 
Trentonian black shales. Kay (1937, p. 274) defined it as "the argillaceous 
limestones and limestone-bearing black shales succeeding the lowest 
Sherman Fall Shoreham limestone and underlying the Stony Point black shale. " 
He measured 145 feet on the west shore of South Hero Island, Vt. , just south 
of the Grand Isle-South Hero town line. The lower 30 feet have 8- to 12- 
inch beds of gray argillaceous limestone interbedded with dark gray 
calcareous shale. Above that the shale is predominant, but limestone beds 
are abundant, 3 to 12 inches thick with undulating surfaces, interbedded 
with half-inch to 12-inch layers of black calcareous shale. Less than one 
third of the Cumberland Head has more than 50 per cent shale, and about 
half has more than 60 per cent limestone beds. Some units as thick as 15 
feet have 80 per cent limestone beds. The proportion of shale increases 
gradually but not uniformly upward. 



Stony Point Formation 

The Stony Point shale was defined by Ruedemann (1921, p. 112-115) as 
"hard, splintery dark bluish-gray calcareous shale" at Stony Point, 1 l/2 
miles south of Rouses Point, N.Y. , on the west shore of Lake Champlain, 
and correlated faunally with upper Canajoharie shale of the Mohawk Valley 
(Middle Trentonian). 

The base of the Stony Point is exposed on the lake shore 0. 55 miles 
south of the breakwater at Gordon Landing, the eastern end of the Grand 
Isle-Cumberland Head ferry. Deposition was continuous from the 
Cumberland Head up into the Stony Point, and the contact is somewhat 
arbitrarily chosen where the proportion of shale increases upward, and the 
wavy, irregular limestone bedding of the Cumberland Head gives way upward 
to smooth, even limestone beds of the Stony Point. The 215 feet of Stony 



153 



Point formation exposed here is interbedded dark gray calcareous shale with 
light-olive-gray weathering, dark gray fine-grained limestone in beds of 
1 to 12 inches, about 70 per cent shale. Two units about 9 feet thick are 
about 80 per cent limestone beds. 

The thickest and least deformed measurable section of Stony Point 
begins 0. 6 mile north of Wilcox Bay and extends for 1. 8 miles northward 
along the shoreline bluffs of northwestern Grand Isle (Hawley, 1957, p. 59, 
87-89). In this section of 635 feet, there are a few gross vertical lithic 
variations which are recognizable throughout this field area. Above the 
lower 215 feet, as described above, the percentage of calcareous shale 
decreases upward. Olive-gray to light-olive-gray weathering, dark gray 
argillaceous limestone appears in increasing proportion through the upper 
400 feet of this section, where the percentages are: argillaceous limestone, 
commonly silty, 66 percent; calcareous shale, 29 percent; fine-grained 
limestone beds, 5 per cent. 

The argillaceous limestone commonly occurs in thin, even beds (one 
quarter to three quarters of an inch) with fine lighter-and darker-gray 
laminae, but occasional beds reach 10 inches. Thicker-bedded zones 
suggest cyclic deposition: from calcareous shale (1 to 4 inches) upward 
through 5 to 6 inches of laminated argillaceous limestone, to a 1- to 3 -inch 
bed of fine-grained limestone; then through 4 to 5 inches of argillaceous lime- 
stone to 1 to 4 inches of calcareous shale. Where the interval between 
calcareous shale beds is thinner, the fine-grained limestone bed in the 
middle is missing. The proportion of silt and argillaceous material in 
harder argillaceous limestone varies greatly. Intricate, fine, current cross - 
bedding occurs in four thin zones, indicating currents flowing northeastward. 

Above this zone rich in laminated argillaceous limestone the proportion 
of calcareous shale increases, and 239 feet near the top of the Stony Point 
is composed entirely of calcareous shale. This shale section, 1.4 miles 
S 370 W from Long Point, North Hero, Vt. , is assumed to represent the 
uppermost part of the Stony Point because it lies on the nose of a long, 
northeastward-plunging anticline between a thick argillaceous limestone 
section to the southwest, and a large area of Iberville shale to the north 
and northeast. 

In this field area it is not possible to measure the entire thickness of 
the Stony Point, but from piecing together several measurable sections a 
minimum thickness is 874 feet. The total thickness is estimated to be 1000- 
1500 feet, allowing for probable thicknesses that could not be measured in 
the middle and upper parts of the Stony Point (Hawley, 1957, p. 83). In 
the log of the Senigon well near Noyan, Quebec, about 4 miles north of the 
international boundary at Alburg, shale apparently equivalent to the Stony 
Point is 924 feet thick (Clark and Strachan, 1955, p. 687-689). 

Iberville Formation 

The Iberville formation was named by Clark (1934, p. 5) for its wide 
outcrop belt in Iberville County, southern Quebec, about 10 miles north of 



15^ 



the international boundary at Alburg, Vt. Clark (1939, p. 582) estimated 
the Iberville to be 1000-2000 feet thick in its type area. 

The base of the Iberville has a gradational contact and was chosen on 
the basis of lithic criteria by which it can be most easily distinguished from 
the Stony Point. The Stony Point is entirely calcareous shale and 
argillaceous limestone with occasional beds of light-olive-gray weathering, 
dark gray fine-grained limestone. Above the lower transition section, the 
Iberville is composed of interbeds of medium to dark gray noncalcareous 
shale (1-12 inches, usually 2-4 inches), moderate-yellowish-brown 
weathering, dark gray laminated dolomitic siltstone (one quarter inch to 
10 inches, usually 1/2- 1 1/2 inches), and occasionally moderate-yellowish- 
brown weathering, dark gray fine-grained dolomite. The most conspicuous 
change from the Stony Point is the appearance of the yellowish-brown 
weathering dolomite beds, and the noncalcareous shale which is more brittle 
and more lustrous on cleavage surfaces than the calcareous shale. The 
transition section is at least 72 feet thick at Appletree Point in northern 
Burlington (Hawley, 1957, p. 64), and may be as thick as 200 feet. A 
section from Stony Point to Iberville is almost continuously exposed, though 
somewhat deformed, along the lakeshore southeastward for a half mile from 
Kibbee Point, in northeastern South Hero Township, Vt. The base of the 
Iberville is defined as the first appearance of the noncalcareous shale and 1 

dolomite beds. |1 

Iberville shale and dolomitic siltstone show remarkable rhythmic ^ 

bedding. The base of each cycle is a sharp contact, sometimes a slightly y 

scoured surface, on which a thin bed (0. 25-0. 75 inch) of yellowish-brown .; 

weathering, dark gray laminated dolomitic siltstone was deposited. The - J, 

typical siltstone layer becomes finer-grained upward with decreasing quartz ( 

and dolomite, and increasing argillaceous and carbonaceous material, and j^ 

grades into dark -gray noncalcareous thin-cleaving shale (1-4 inches). 
Usually at the top is an eighth to three quarters of an inch of grayish-black 
shale interlaminated with the dark gray. Occasionally the dolomitic 
siltstone may be missing at the bottom of the cycle, or the grayish-black 
shale laminae missing at the top. Ripple-drift cross-lamination is a common 
feature of the dolomitic siltstone layers. In some beds only a single story :^ 

of ripples were built, but in others down-current ripple drift continued long f, 

enough to form two, and occasionally three or four tiered beds. Current j; 

directions indicated by the ripple cross-lamination are invariably south- 
westward in the Iberville, in contrast to northeastward in the Stony Point. 

Six thicker (5-10 inches) non-laminated graded siltstone beds with \, 

1 mm. -long shale flakes in their lower parts are found on northeastern 
Burton Island, southwest of St. Albans Point. They grade finer upward, and ^ 

some are laminated above the lower third. One has large (5 by 1 l/4 inches 
is the largest) angular shale fragments in the mid-portion. They commonly 
have contorted lamination in the middle, above which lamination is more 
marked, and they are topped with drift ripples grading upward into shale. * 

The thickest measurable sections of the Iberville are 732 feet, with 
an estimated 2200 depositional cycles, on the west side of Woods Island, 



155 



and 304 feet with an estimated 1215 cycles on Clark Point, southwestern 
Hog Island. West Swanton, Vt. The cyclic character of the Iberville layers, 
the graded beds, graded laminated beds, and convolute laminae, are all 
characteristic of sedimentation by turbidity currents (Kuenen, 1953; Bouma, 
1962, p. 48-54). 

Hathaway Formation 

The Hathaway formation, named for Hathaway Point on southeastern 
St. Albans Point. Vt. (Hawley, 1957, p. 68), designates argillite and bedded 
radiolarian chert, commonly intensely deformed, with included small 
fragments to large blocks of quartz sandstone, coarse graywacke, dolomite, 
limestone, and chert. Some fragments strongly resemble dolomite and 
dolomitic siltstone beds of the underlying Iberville, but the coarse sandstone, 
chert and graywacke are unlike any strata in the autochthonous formations of 
the Champlain lowland. The graywacke resembles the earliest Cambrian 
Pinnacle Formation, which outcrops in a north-south trending area 8 to 10 
miles east of northern Lake Champlain (Stone & Dennis, 1964, p. 19). 
Where the Hathaway and Iberville are in contact or close proximity, there is 
marked disparity in intensity and nature of their deformation. The Hathaway 
appears to have deformed by flowage without the development of good 
cleavage, commonly with disintegration of less mobile beds into blocks and 
boulders. The Iberville has undergone much less intense folding and faulting, 
of a type normally associated with the regional structure. For these reasons, 
the Hathaway is inferred to be a submarine slide breccia initially deformed 
while its muddy constituents were still soft. 

The best accessible exposures of the Hathaway are on Hathaway Point, 
and extending north for 1200 feet from Beans Point on the east shore of the 
lake, in northwestern Milton Township, Vt. As fate would have it, the most 
impressive and extensive exposures of the Hathaway are on Butler Island, 
between St. Albans and North Hero, accessible only by boat. Almost all of 
Butler Island is composed of the Hathaway, which is usually a mashed, 
streaky light and dark gray argillite with inclusions of dolomite, dolomitic 
siltstone, and occasionally black chert and graywacke, from 1 by 2 to 8 by 
24 inches. On the southeast side of Butler Island are found the largest 
inclusions in the Hathaway: blocks of dolomitic siltstone up to 3 by 20 feet, 
and coarse-grained graywacke up to 15 by 50 feet. Argillite foliation wraps 
around these blocks, and around innumerable smaller pebbles and boulders. 
Hawley has described in detail these and other localities (1957, p. 68-75). 

Summary of De positional History 

The fossiliferous limestones of the Glens Falls and older formations in 
this area indicate rather shallow, clear-water carbonate deposition, often 
in an environment of considerable wave and current turbulence (reefs, 
coarse calcarenites, and cross-bedding in the upper Chazyan). In the 
Cumberland Head formation fossils are much scarcer and there is a 



156 



transition from the shallow water carbonate environment to a muddier, deeper 
water depositional environment. The lower two hundred feet of the Stony 
Point is 70 per cent calcareous shale, and the next 400 feet is laminated 
argillaceous limestone (66%) interbedded with calcareous shale (29%) and 
hard, purer fine-grained limestone (5%) in a somewhat cyclic pattern. 
Current cross-lamination indicates flow toward the northeast. The complete 
absence of primary structures associated with shallow water, and the fine 
lamination of the argillaceous limestone, and the paucity of fossils, suggest 
a deeper, quieter, muddier depositional environment. 

Through the lower hundred feet (or more) of the Iberville, a marked 
change in the character of the rock appears with dolomite replacing limestone 
as the hard, fine-grained interbeds, and noncalcareous shale replacing the 
calcareous shale of the Stony Point. At some unknown distance above the 
base, a section of at least 730 feet shows cyclic interbedding of non- 
calcareous shale and graded, laminated dolomitic siltstone commonly with 
current cross -lamination. The currents flowed toward the southwest. This 
suggests the changed character of the rock is at least partly the result of a 
change from a westward source of sediment (for the Stony Point), to an east- 
ward source for the Iberville, and that turbidity currents dominated the 
depositional character of the Iberville. Uplift of deep sea bottom east of the 
Champlain Valley in late Mohawkian and early Cincinnatian time could have 
provided the new source of sediment and the westward slope down which 
the turbidity currents flowed. Some simultaneous deepening of the Champlain 
Valley region also occurred. 

The Hathaway formation, composed of argillite and bedded radiolarian 
chert, chaotically deformed, with included masses of limestone, dolomite, 
dolomitic quartz siltstone and sandstone, coarse graywacke, and chert, is 
interpreted as a submarine slide breccia. Some of the types of inclusions, 
particularly the graywacke and chert, are unknown in autochthonous under- 
lying formations of the Champlain Valley and in regions to the south and 
west. The slide (or slides?) seem to have come from the east, down the 
slope suggested by the direction of flow of turbidity currents which deposited 
sediment in the Iberville. The Taconic orogeny was occurring at this time, 
and some believe that the major thrusts of western and northwestern Vermont 
accompanied this orogeny. If this be true, thrust fault escarpments on the 
sea bottom to the east of the Champlain Valley could account for the slides 
and the assemblage of inclusions in the Hathaway. Earthquakes associated 
with the Taconic orogeny may have triggered the turbidity currents of the 
Iberville. 

Tectonic Deformation 

The shales are complexly folded and sheared, with fold axes trending 
a little east of north in the southern part of the area, and swinging more 
toward the northeast (N 20° - 30° E) in the north. Although elongate narrow 
belts of intense deformation parallel fold trends, separated by broader belts 
of more gentle folding, general intensity of deformation increases toward the 



157 



Champlain and Highgate Springs thrusts. In areas underlain by shale, 
particularly in North Hero and Alburg, the topographic "grain" of long, low 
hills accurately reflects the trends of fold axes. From Grand Isle north- 
ward the smaller folds plunge northward and southward, but the pattern of 
structural elements and formational boundaries indicates the northeastward 
plunge is more prevalent and perhaps a bit steeper. The area might be 
visualized as having northeastward trending folds imposed on an eastward 
regional dip, though there are many individual exceptions to this generalized 
picture. 

Fracture cleavage is nearly everywhere present in the more argillaceous 
beds of the Stony Point and Iberville formations. The term is used here as 
defined by Swanson (1941, p. 1247), "the structure is due to closely spaced 
planes of parting a certain small distance apart," and "as a rule it is 
possible to see that the rock between the planes of parting. . .has no 
structure parallel to them, or at most any parallel structure is confined to a 
thin film along the parting planes. " In these shales, cleavage planes are 
more closely spaced in belts of intense folding, and, under the same 
structural conditions, they are more closely spaced in more argillaceous beds 
than in more calcareous beds. Fracture cleavage plates in the argillaceous 
limestone of the Stony Point formation commonly range from one half inch to 
5 inches thick. Fracture cleavage in calcareous shale is finer, and in the 
noncalcareous shale of the Iberville the planes are so close as to resemble 
flow cleavage (Swanson, 1941, p. 1246), but in thin section cut 
perpendicular to the finest cleavage, it is seen to be composed of somewhat 
irregular and discontinuous joint-like fractures 0.02 to 0.05 mm. apart. 
Bedding displacements of 0.01 to 0.04 mm. occur along the cleavage planes 
(Hawley, 1957, p. 82). 

Although innumerable faults cut the shales, only a few displace them 
enough to juxtapose different formations. On most faults the rock of both 
walls is so similar that only minor displacement can be assumed. Block 
faulting typical of the western and southern Champlain Valley is distinct only 
in the older Trenton, Chazy, and Canadian formations of western South Hero, 
where Kay and his former students have mapped them (personal communication). 
Shear along bedding surfaces, cleavage surfaces, and at varying angles to 
both is very common. In more intensely folded belts, multiple shears occur 
along crests and troughs of folds. The bearing of slickensides is remarkably 
constant, regardless of the attitude or type of surface on which movement 
occurred. Of 119 slickensides bearings measured in this area, only three 
lay outside the arc between N 25° W and N 85° W (Hawley, 1957, p. 81). 

Field Trip Stops 

The best exposures of the shales and limestone are along the lake- 
shore bluffs. During the spring months and after long periods of heavy 
rain, the lake may be higher than normal, and many of these exposures may 
be inaccessible. Field localities are shown in Fig. 1. THE STOPS ARE ON 
PRIVATE LAND. PERMISSION HAS BEEN OBTAINED FOR THE STOPS WE WILL 



158 




Figure 1. Trip 5 - Field trip stops. 
Scale: 1 in. =4 mi. 



159 



VISIT THOSE WHO MAY WISH TO VISIT THESE LOCALITIES IN THE FUTURE 
SHOULD GAIN PERMISSION FOR EACH VISIT. GIVE GEOLOGY A GOOD NAME 
BY BEING VERY THOUGHTFUL. 



GREAT BACK 
BAY 



O 



Clay Poini 




Figure 2. Stop 1, Clay Point. Scale: 1:24,000. 

Stop 1. Clay Point, between Malletts Bay and the Lamoille River, east 
shore of lake. (Fort Ethan Allen Quad. , 1:24,000). THIS PROPERTY IS 
POSTED, AND PERMISSION MUST BE OBTAINED. In the transition beds in 
the lower Iberville (interbedded calcareous and noncalcareous shale, with 
argillaceous limestone, argillaceous dolomite, fine-grained dolomite, and 
silty-laminated dolomite with current cross-bedding) there is a small, 
overturned anticline cut by small thrust faults. The relationship of 
cleavage to bedding, plunge of the fold, identification of tops by cross- 
bedding, and the faulting make this a worthwhile stop for a structural geology 
class. 



Stop 2 - From Kibbee Point (northeastern South Hero) southeastward along the 
shore for 2500 feet, is exposed the transition from Stony Point to Iberville 
formations. (South Hero Quad. , 1: 24,000). With a few minor rumples the 
dip is southeastward all the way to a deep gully and small bay which 
separate a steep bluff-point to the east from the shore northwestward to 
Kibbee Point. This bluff, 2800 feet SE of Kibbee Point is composed of 
Stony Point argillaceous limestone and calcareous shale, overturned and 
dipping 5 5° southeastward. Thus, the gully conceals the faulted core of 
an overturned syncline. The fault is very likely a thrust, east side up. 

West of the gully is Iberville, about 90% finely cleaved 
noncalcareous shale, with interbedded silty cross-laminated dolomite. 
Northwest from here to Kibbee Point the proportion of calcareous shale 



160 



Gordon Land* 



Cooper Pt 



Rockwell 



Sawyei^^ 



Barnes 



Mc Bride 




Sat"^*'' 



Beech Bay 
Jackson Pt 



Fish Bladder /V 

a, 

C.d.r 1^ 
t5 



Figure 3- Stops 2-5, South Hero Island. Scale: 1:62,500. 

increases. About 220 feet southeast of Kibbee Point the southeastward- 
dipping beds are massive calcareous shale (Stony Point fm.). About 900 feet 
south of Kibbee Point on its west shore the Stony Point beds still lower in 
the section are predominantly argillaceous limestone, interbedded with 
calcareous shale. 

Stop 3. Road cut on US 2, at the southwest corner of Keeler Bay, 1 mile 
south of junction with Sunset View Rd. (South Hero Quad. , 1:24,000). The 
road cuts northward across a NE'ward plunging anticline in the Stony Point 
formation. The rock is dominantly silty -lamina ted argillaceous limestone 
with some calcareous shale, and is inferred to be in the thick argillaceous 
limestone zone in the middle of the formation. There are conspicuous 



161 



bedding-plane slickensides on the west side of the road. Rotational offset 
along fracture of cleavage can be seen by matching silty laminae across the 
fractures. On the east side of the road, harder fine-grained limestone beds 
(5" i ) have buckled and overlapped. 

Stop 4. Small quarry in Glens Falls Ls. , . 1 mile S of Sunset View Road, 
.6 west of US 2. (South Hero Quad. , 1:24,000). This thick-bedded lime- 
stone with fossiliferous zones (1-3") at intervals of 1 to 5 inches, will 
serve to dramatize the change to predominantly shaley rocks in formations 
younger than the Glens Falls. The area of the quarry has been mapped as the 
Larrabee member. (Erwin, 1957). 

Stop 5. West shore of South Hero Island, extending for one mile southward 
from the breakwater at Gordon Landing. (South Hero Quad. , 1:24,000). The 
lower 215 feet of the Stony Point formation is exposed between the break- 
water and the top of the Cumberland Head formation, 2900 feet to the south. 
In the next 2300 feet of shoreline, the upper 145 feet of the Cumberland Head 
formation is exposed. These sections are described in the text article. The 
south end of this section is cut off by a right lateral wrench fault striking 
N 59° W. dipping 79° NE. South of the fault the interbedded limestone and 
shale (about 79% Is. , 30% sh.) have been mapped as the Shoreham member 
of the Glens Falls formation (Erwin, 1957) on the basis of lithology and the 
presence of Crvptolithus. 

Stop 6. Road cut on east side of US 2 halfway between City Bay (North Hero 
Beach roadside park) and Carrying Place. (North Hero Quad. , 1:24,000). 
This outcrop shows the interbedded laminated argillaceous limestone and 
calcareous shale typical of the middle section of the Stony Point formation. 
It lies close to the axis of a major, northeastward plunging anticline. 

Stop 7. Middle point on north side of Gary Bay, North Hero, 2000 feet east 
of Blockhouse Point. (North Hero Quad. , 1:24,000). Typical Iberville 
cyclic bedding is exposed for about 1500 feet along this shore, extending 
eastward from the place where the access road meets the shore. From west 
to east are: an asymmetrical syncline, an asymmetrical anticline, and to 
the east of a covered interval is the east, overturned limb of a large 
syncline. These folds are in the axial area of a large, northeastward 
plunging, overturned syncline. Relationships of cleavage to bedding, axial 
surfaces, and direction of plunge are well shown. Small-scale current 
cross-lamination on some beds indicates southwestward flow. 

Stop 8. Quarry in Iberville (mislabelled "gravel pit" on No. Hero Quad. , 
1:24,000), 1.6 miles S 10° E from east end of North Hero-Alburg bridge. 
The beds are almost flat-lying, and only about 15 feet of section is 
exposed, but it is typical cyclic deposition, and the details are well shown. 



162 




Figure 4. Stops 6-8, North Hero Island. Scale: 1:62,500. 

Stop 9. Upper Iberville beds in quarry (mislabelled "sand and gravel pit" 
on East Alburg Quad. , 1: 24,000) 1800 feet north of Vt. Hwy 78 and 600 feet 
west of Campbell Road, northern Hog Island, West Swanton. The quarry exposes 
an overturned anticline, thrust faulted on the upper, eastern limb, with 
adjacent syncline immediately westward, also faulted. 

Stop 10. Southernmost tip of St. Albans Point, on property of former Camp 
Kill Kare, now a state park. (St. Albans Bay Quad., 1:24,000). Northeast- 
ward plunging asymmetrical anticline with linked small syncline northwest 
of it, in Iberville noncalcareous and calcareous shale with dolomitic 
interbeds. 

Stop 11. Between Camp Kill Kare's access road and the lake, about halfway 
between the private cottages and the Camp buildings. (St. Albans Bay Quad. , 
1:24,000). There are 31 feet of white weathering, grayish-black chert in 
beds of 2 to 6 inches, dipping steeply (69°) southeastward on the southeast 
flank of the anticline at Stop 9. Structurally overlying the chert beds is 



163 




./-■ 



Figures. Stop 9, Northern Hog Island. Scale: 1:24,000. 




Figure 6. Stops 10-13, St. Albans Bay area. Scale: 1:24,000. 



164 



black siliceous argillite in which bedding is not apparent because of its 
irregular, chippy foliation. The argillite contains rounded pebbles (avg. 1 by 
2 inches) of gray dolomite and fragments of chert. Some graptolites were 
found in the argillite, but smearing precluded identification. This is part 
of the Hathaway formation. It is likely that the chert beds here represent 
a larger mass involved in a submarine slide. 

Stop 12. Hathaway Point, at the south end of St. Albans Point. (St. Albans 
Bay Quad. , 1:24,000). This is the type locality for the Hathaway formation. 
It has a matrix of pale-greenish-yellow weathering rock seen on a polished 
surface to be composed of small, irregular, curdled masses of greenish-gray 
to olive-gray argillite. Streamed and isoclinally folded in the matrix is 
black siliceous argillite similar to that associated with the chert beds at 
Stop 11. "Floating" in the matrix are small masses of grayish-black 
radiolarian chert which are commonly angular, as well as masses of bedded 
chert measurable in tens of feet. Fragments of dolomite and dolomitic 
siltstone occur in the western part of the Hathaway point exposure. 
Numerous slickensided tectonic shears are present in a variety of 
orientations. One 40-foot wedge between shears is composed of isoclinally 
folded calcareous and noncalcareous shale with occasional boudinaged masses 
of fine-grained limestone, resembling the transition beds at the base of the 
Iberville. Both of the islands east of Hathaway Point, in the middle of the 
bay, are composed of chaotically deformed argillite and chert. It is 
assumed that St. Albans Bay may lie over a deep synclinorium. 

Stop 13. Lime Rock Point, on the southeast side of St. Albans Bay. (St. 
Albans Bay Quad. , 1:24,000). At the base of the bluff composed of the 
Beldens (Upper Canadian) crystalline limestone with buff-weathering 
dolomitic beds, there is a dramatic exposure of the Highgate Springs over- 
thrust; lower Ordovician Beldens Limestone over upper Ordovician Iberville 
calcareous and noncalcareous shale with occasional beds of yellowish- 
brown weathering fine-grained dolomite and silty dolomite. At the base of 
the high, steep bluff about one half mile to the east is the Champlain over- 
thrust, on which the lower Cambrian Dunham dolomite is thrust westward 
over the Beldens. South of Lime Rock Point the Highgate Springs thrust 
slice is overlapped by the Champlain thrust for two and a half miles. It 
reappears for four miles, and then disappears again under the Champlain 
thrust, southeast of Beans Point. This is as far south as the Highgate 
Springs slice can be traced. 



Stop 14. Beans Point, east shore of lake in northwest Milton. (Georgia 
Plains Quad. , 1:24,000). The Hathaway crops out intermittently for 1200 
feet north from Beans Point. This is in a zone of intense deformation close 
to the Highgate Springs thrust, the trace of which is covered, probably 
about 600 feet back from the shore. The base of the steep bluffs 2000 feet 
back from the shore marks the trace of the Champlain fault, on which lower 
Cambrian Dunham dolomite has been thrust over Beldens crystalline 



165 



Camp Ric 



^ 



Camp Watson 



Eagle Mountairij 
tO Camp 




Figure 7. Stops 14 & 15, Northwestern Milton. Scale: 1:62,500. 

limestone and dolomite of the Highgate Springs slice. 

The Hathaway is composed of boulders and fragments "floating" in 
mashed argillite. The argillite is mottled olive gray to dark greenish gray 
to greenish black. On a polished surface cut perpendicular to foliation the 
mottled colors are seen to represent original bedding which has been folded 
most intricately, and sheared with no development of slickensides or breccia. 
The small-scale shearing has completely healed, and some minute fold crests 
merge into the adjacent bed, a streaming of one bed into the next with no 
sharp boundary. Included in the argillite are rounded fragments of moderate- 
yellowish-brown weathering, dark gray fine-grained dolomite and cross- 
laminated dolomitic siltstone, sub-angular to rounded, up to 4 by 7 by 20 
inches in size. The long axes of the boulders are approximately parallel, 
plunging about 55° toward S 45*-* E. Foliation causes the argillite to split 
into irregular tapered chips. Thirty-six feet of cover separates the north 
end of the Hathaway outcrop from cyclic-bedded upper Iberville which lies 
overturned, dipping 4 6° northeastward. 

Stop 15. Camp Watson Point, 3/4 mile south of Beans Point (Stop 14). 
(Georgia Plains Quad. , 1:24,000). The core of a large, overturned syncline 
is exposed on the point, plunging 18° toward N 56° E. The overturned limb, 
dipping 29° southeastward, is exposed for 200 feet or more along the shore 
to the south. The rock is lower Iberville transition, with interbedded 
calcareous and noncalcareous shale, argillaceous limestone, and silty 
laminated dolomite. 



166 



References for Trip 



Bouma, A. H. , 1962, Sedimentology of Some Flysch Deposits: Amsterdam/ 
New York, Elsevier Publishing Co. , 168 p. 

Clark, T. H. , 1934, Structure and stratigraphy of southern Quebec: Geol. 
Soc. America Bull., v. 45, p. 1-20. 



, 1939, The St. Lawrence lowlands of Quebec, Pt. 1 of 

Canadian extension of the interior basin of the United States: 
Geologie der Erde, v. 1, p. 580-588, Berlin, Gebruder Borntraeger, 
643 p. 

Clark, T. H. , and Strachan, Isles, 1955, Log of the Senigon well, southern 
Quebec: Geol. Soc. America Bull. , v. 66, p. 685-698. 

Gushing, H. P. , 1905, Geology of the northern Adirondack region: N.Y. 
State Mus. Bull. 95, p. 271-453. 

Erwin, Robert B. , 1957, The geology of the limestone of Isle La Motte and 
South Hero Island, Vermont: Vermont Geol. Survey Bull. 9, 94 p. 

Fisher, Donald W. , 1968, Geology of the Plattsburgh and Rouses Point, 
New York -Vermont, Quadrangles: N.Y. State Mus. and Science 
Service, Map and Chart Ser. No. 10, 51 p. 

Hawley, David, 1957, Ordovician shales and submarine slide breccias of 
northern Champlain Valley in Vermont: Geol. Soc. America Bull. , 
V. 68, p. 55-94. 

Kay, Marshall, 1937, Stratigraphy of the Trenton group: Geol. Soc. 
America Bull., v. 48, p. 233-302. 

Kuenen, P. H. , 1953, Significant features of graded bedding: Am. Assoc. 
Petroleum Geologists Bull. , v. 37, p. 1044-1066. 

Ruedemann, Rudolf. 1921, Paleontologic contributions from New York State 
Museum: N.Y. State Mus. Bulls. 227, 228, p. 63-130. 

Stone, S.W. , and Dennis, J.G. , 1964, The Geology of the Milton 
Quadrangle. Vermont: Vermont Geol. Survey Bull. 27, 79 p. 

Swanson, C.O. , 1941, Flow cleavage in folded beds: Geol. Soc. America 
Bull. , V. 52, p. 1245-1264. 



167 



Trip 7 

ROTATED GARNETS AND TECTONISM IN SOUTHEAST VERMONT 

by 

John L. Rosenfeld 

Department of Geology 

University of California, Los Angeles 

Conventional structural and s trat i graphic data (fig. l--based 
primarilyon Do 11 e_taj_., 1961) and their topological implications 
suggest that during the late Paleozoic two large, recumbent, iso- 
clinal, sigmoid folds in Paleozoic, metamorphosed, stratified rocks 
of southeast Vermont (Table 1) predated the mantled gneiss domes 
with which they are associated. One of these folds involved units 
strat i graphica 1 1 y and structurally beneath the S i 1 uro-Devon ian cal- 
careous and non-calcareous schists of the Waits River formation. 
The other, involving S i 1 uro-Devon ian units structurally above but 
of otherwise undemonstrated s trat i graphi c relationship to the same 
unit, is exposed in culminations associated with seven domes. The 
approximate axial parallelism of these folds and the opposite rota- 
tions of their short limbs suggest that these folds resulted from 
westward extrusion of rocks in between. 

Using methods described elsewhere (Rosenfeld, 1970), regional 
study of spirally arranged inclusions In garnets and rotations deter- 
mined therefrom confirms the early presence within the Waits River 
formation of a surface, quas i -para 1 1 e 1 to the bounding strata now 
exposed to the east and west, across which the rotational senses 
possessed mirror symmetry (Rosenfeld, 1968). After graphical cor- 
rection for effects resulting from rise of the gneiss domes, the 
rotational axes of the garnets parallel those of the giant recumbent 
folds; and the rotational senses of the garnets are those to be 
expected from flexure slip folds having the observed rotations of 
their short limbs (fig. 2; Rosenfeld, 1968, p. 193). 

In further accord with the westward extrusion are: 

(1) pebbles and former phenocrysts in the eastern part of the 
area extremely elongated in the direction of extrusion; also a prom- 
inent mineral llneatlon in the same direction (observable on Putney 
Mountain-Windmill Mountain Ridge; Rosenfeld, 1968, p. 197-199); 

(2) boudinage In the eastern part of the area with fractures 
quas i -para 1 le 1 to the corrected rotational axes of the garnets; 
these give way to the west to compress lona 1 folding of the same 
orientation (observable in central Vermont just east of the Green 
Moun ta I ns ) ; 

(3) an angular divergence in a westerly direction of about 10 
degrees between the Standing Pond formation on one side of the Waits 



168 




veRMONT y /' 

MA5SKHUSETTS g 



1 Strafford Dome 

2 Pomfret Dome 

3 Cfiesler Dome 

4 Alliens Dome 

5 Guilford Dome 

6 Colrain Dome 

7 Shelburne Falls Dome 

8 Townshend-Brownmgton Syncline 

9 Ascutney Sigmoid 
10 Star Hill Sigmoid 43»oo- 

g Gile Mountoin Formation 

^^1 Standing Pond Volcanics 

r~ I Ptiyllites and calcareous sctiists 

' ' of Northfield and Woits River 

Formations , Littleton Formation 

S Silurian conglomeratic tiorizon 

€ Early Cambrian (?) horizon 

U l^aior unconformity beneatti Paleozoic 

A Ascutney StocK (post-metomorphic) 

X Syntectonic granite 

d Pre- Silurian ultramofic 

WRa, SPa ( see Table i ) 



20 KILOMETERS 



Fig. 1 



Field tnp slops italicized 



169 




SI5b 
(Stop 3) 



VERTICAL = HORIZONTAL 



Fig. 2 



170 



Table 1 

Condensed Chronologic Table of Metamorphosed Rocks 
( See Doll etal. , 1961 , for more details) 



Geologic Age 



Unit or Feature 



Lithology 



Devonion (') 



New Hampshire Plutonic Series 



Late synkinemotic granitic rocks 



Devonian* 



Glle Mountain Formation, 
Littleton Formation (?)* 



Quortzo-feldspathic sctiist, graphitic 
schist, some calcareous 



Siluro-Devonian 



Siluro-Devonlon 



Standing Pond Volconlcs 
■UNCONFORMITY (?) {SPa )^»~ 
Northfleld and Waits River Formations, 
Littleton Formation (?)* 

-=(»»'/<?0)=!= 



Chiefly amphibolites, greenschists 
of volcanic origin 



Graphitic calcareous and non-calcareous schist 



Silurian 
Late Ordoviclan 



Show Mountain Formation 
-UNCONFORMITY- 
Ultramafic intrusives 



Quartz conglomerate, porphyritic volconics 
Dunite, serpentinite, steatite 



EarlyCambrian to 
Mid-Ordovician 



Pinney Hollow through 
Missisquoi Formotions 



Heterogeneous schists, hornblende 
gneisses and amphibolites 



Late Precambrion to 
Early Cambrian 

Precambrion 



Cavendish through 
Hoosoc Formations 
-MAJOR UNCONFORMIT' 

Mt Holly complex 



Augen gneiss, conglomerate gneiss, albitlc 
and poragonltic schist, dolomite 

Assorted gneisses, granites, schists, 
amphibolites, and marbles 



* The direction of facing across the Standing Pond Volconics is still uncertain. I hove followed 
Chong e/ (7/ , 1965, in elevating this unit to formational status. Implications of the 
alternative possibilities are discussed in their paper (p 40, 56-62). 



171 



River formation and the Shaw Mountain formation strat i graphica 1 1 y 
beneath it (further possible indication of this divergence appears 
in the easterly offset of negative gravity anomalies (Bean, 1953, 
p. 528-533) in the Strafford and Pomfret domes). This divergence 
is particularly evident south of the Ascutney stock (fig. 1); 

(if) "downstream" folding oriented in a westerly direction to 
the west of a large pre-Silurian dunite mass (observable in the 
eastern part of the Wilmington Quadrangle west of the East Dover 
ultramafic body mapped by Skehan, I96I). 

Analysis of the rotations represented by the garnets indicates 
that the Green Mountain ant ic 1 I nor i urn, although present in older 
strat i graphic units at the time, manifested itself as a rejuvenated 
ant ic 1 i nor i urn within the S i 1 uro-Devon i an strata only after the west- 
ward extrusion and contemporaneously with the development of the 
mantled gneiss domes to the east. the ant ic 1 i nor i urn therefore did 
not form a barrier to the westerly extrusion and consequent loading 
of areas to the west. This earlier ant ic 1 i nor i urn may be related to 
an earlier Paleozoic metamorphism evident in rotated garnets con- 
taining growth-rotation "angular unconformities" (loc. S35J, fig. 2). 

The shear senses and orientations of conspicuous minor folds, 
commonly at high angles to the early (inner) rotational axes of the 
garnets, give evidence of later up-thrust of the gneiss domes (fig. 
2; Rosenfeld, 1968, p. 193). The surfaces included in the outer 
parts of the garnets also reflect gradual transition to late rota- 
tions of the garnets about axes parallel to the folds and of similar 
rotational senses. The high angle between the early and late rota- 
tional axes of the garnets, both of which must have paralleled the 
schistosity at their respective times of growth, permits apportion- 
ment of the rotation. On the east limb of the Chester Dome, garnets 
at one locality show 625° rotation for the early stage of deformation 
and 105° for the late stage. 

Interpretation of the proximate mechanism of diastrophism for 
the early and major diastrophic event depends primarily upon knowl- 
edge of the as yet unknown age relationship of the units bounding 
the Waits River formation on the east. If these units should prove 
older than the Waits River formation, the indicated westward trans- 
port of material may be ascribed to flexure-slip folding of the west- 
ward-opening lower half of a giant, initially recumbent, sigmoid 
fold whose upper half is nowhere exposed in eastern Vermont. If 
the same units should prove younger than the Waits River formation, 
the transport may be ascribed to westward intrastratal extrusion of 
the relatively dense Waits River formation, possibly down a gently 
inclined slope tilted toward the west. It is thus of great impor- 
tance to resolve this ambiguity by development of procedures for 
resolving the above s trat i graph ic uncertainty. 



172 



Road Log for Trip 7 



pass 
west 
boun 
cal 1 
r i gh 
he 1 p 
so t 
cont 
Name 



Road lo 
over the 
of North 
dary of th 



g begins on 
east range o 
Windham, Ver 
e Saxtons Ri 

mmer'' 



larg 
thes 



1 a "no hammer " trip , 
t . I'd 1 i ke to en i i St 
ing to preserve the hi 
hat future geologists 
ext. May these featur 
s of units and major s 
ol 1 e_t a±. , 
es before un 



e 1 y from D 
e referenc 



Route 1 
f the G 
mont, a 
ver Qua 
a 1 thoug 
the as 
ghl y V i 
will be 
es avoi 
tructur 
1961, a 
der taki 



1 , just we s 
reen Mounta 
bout 200 fe 
drang le . J 
h CO 1 1 ect i n 
s i s tance of 
s i bl e mi nor 
able to se 
d the "trag 
al features 
nd Rosenfel 
ng this exc 



t of the summit of the 
i ns , 0.5 mi les sou th- 
et west of the west 
hi s excurs i on i s bas i - 
gat Stop 3 is all 
all pa rtici pants in 

structural features 
e them in the i r field 
edy of the commons'." 

referred to below are 
d, 1968. A perusal of 
ursion will be helpful 



Mi leaqe 



0.0 STOP ]_. Anqu lar unconformi ty between the over lying pro - 

ira tes of the Tyson forma t i on 



0.6 
0.8 



2.2 



2.6 



h.O 



7.6 

8.0 



grade metamorphosed cong lome 
and the under lying retroqrad 
tites of the Precambr i an Mou 



formity is significant for t 
the direction of stratigraph 
Route 1 1 through the Hoosac 
North Windham. Turn right o 
Northernmost exposures of Tu 
of Hoosac formation outcrop 
through schists of Finney Ho 
Near crest are exposures of 
Pinney Hollow formation. St 
green amphiboles. Continue 
forma t ions . 

STOP 2. Fi rs t rotated game 
wes t corner of i n tersect i on . 
formation show small counter 
about nearly horizontal axes 
direction ( tl.e d i r ec t i on of 
otherwi se s te ted ) . Proceed 
Road past outcrops of Stowe 
Whetstone Hill member of the 
Windham Center. From here a 
lies within the banded rusty 
the Ottauquechee formation. 
most evident in the field in 
amphibolites to dark green t 
Windham Center we cross the 
of which plagioclase more ca 
not found, regardless of bu 1 
isograd is related to a misc 
clase feldspar series. 
South Windham. Chester amph 
Jama i ca- Tovynshend town line, 
magnet i te-chlor i te-ser ici te 



e me tanior ph i c rocks and pegma - 

nt Ho 1 1 y comp I ex . This uncon- 

his trip because it demonstrates 

ic "tops." Proceed easterly on 

forma t i on . 

nto Rt . 121. 

rkey Mountain member (amphi bol i te ) 

in draw to west. Continue 

1 low format i on . 

Chester amphibolite member of 

rong down-dip lineation of pale 

through Ottauquechee and Stowe 



t loca 1 i ty i n outcrop at 

st of S 

n after 

nor the 

ent 1 y lu 
. 121 o 



Game 

c lockwi 

when V 

V i ew us 



souther 

forma t i 

Missis 

Imost t 

-wca the 

R i se i 

the tr 

b 1 ack 

1 i goc 1 
Ic ic th 
k compo 
i bi t i ty 



ts i n sch i 
se rota t i o 
iewed in a 
ed subsequ 
1 y from Rt 
on and rus 
quoi forma 
o South Wi 
ring graph 
n me tamo rp 
ans i t i on f 

amph i bo 1 i 
ase isogra 
an near 1 y 
s i t i on of 

gap wi th i 



nor th - 
towe 

growth 
rly 
n less 



ty shal 
t i on . 
ndham, 
i t ic sc 
hie gra 
rom pal 
tes . N 
d, nort 
pure al 
the roc 
n the p 



n Windham 
es of the 

the road 
hi s ts of 
de i s 
e green 
ear 
hwes t 
bi te is 
k. This 
lag io- 



i bo 1 i te . 

Enter the typical green garnet- 
schist comprising the main part 



l! 

ti 



II 



173 



of the Pinney Hollow formation and through which the road 
passes for the next 2.0 miles. 

10.0 Turkey Mountain member appears on ridge to west. From here 
to West Townshend we pass from the Pinney Hollow formation 
into the characteristic albite schists of the Hoosac forma- 
tion. 

10.7 West Townshend, ancestral home of the Tafts of Ohio. Turn 
left onto Rt. 30 and proceed southerly through a tectonically 
compressed section from Hoosac to the base of the Missisquoi 
format ion . 

11.1 Base of Missisquoi formation. Continue in typical "pinstripe" 
quar tzofe Idspa thic schists of Moretown member of Missisquoi 
format i on . 

11.6 Readouts on west side of highway show eastward dipping beds 
of "pinstripe" in Moretown with a prominent boudinage frac- 
ture of horizontal orientation. Continue in highly contorted 
schists and amphibolites of the Moretown across the axis of 
the Townshend-Brown i ngton syncline onto the west limb of the 
Athens (pronounced Aythens) dome. 

12.8 Thin amphibolites in smooth outcrops of Moretown on the left 
exhibit boudinage. 

13.1 Park cars in parking area on right at Townshend Flood Control 
Dam. STOP ^ is in the roadcut on the northeast side of the 
highway opposite the dam. Rotated garnets s hov; i n q counter - 
c lockwi se rotat ion on the west 1 i mb of the Athens dome. Note 
the relative consistency of the shear sense indicated by the 
rotated garnets in contrast to that of the drag folds. The 
origin of this contrast has been discussed elsewhere 
(Rosenfeld, 1970, p. 92). Garnets observed here are believed 
to have grown and rotated before development of the Athens 
dome during the lateral extrusion toward the west. The rel- 
ict "oligoclase isograd" may be observed in the form of 
coexistent albite, oligoclase, and clinozoisite encapsulated 
in garnets at this locality (Rosenfeld, 1970, p. 90-91), 
even though the staurolite isograd is only a few tens of 
feet to the east. Note the large boudinage fractures in 
amphibolites here. Proceed southeasterly on Rt. 30 through 
a compressed but apparently complete section from the 
Moretown to the Hoosac formation. 

13-5 Scott Covered Bridge on right. Amphibolite in what is 

believed to be Hoosac formation on left. If these rocks 
correlate with the main band of the Hoosac to the west, 
they are of a distinctly more banded and gneissic facies. 
Just beyond the bridge on the left are some very nice second- 
ary drag folds on a large fold, incompletely exposed in the 
outcrop . 

13.8 STOP k. Cong lomerate qne i ss of Tyson format i on (2) on west 
i n contact with Bu I 1 Hill qne i ss member of Cavend i sh forma - 
t ion ■ The Bull Hill gneiss characteristically has coarse 
microcline augen and is of granitic composition. However, 
it is also a rather widespread s tra t i graph ic unit on the 



17^ 



Chester and Athens domes. It is therefore possible that 
the Bull Hill gneiss represents a metamorphosed stack of 
rhyolitic volcanics. In the southern part of the Athens 
dome, it has not been possible to delineate accurately the 
boundary between the Bull Hill gneiss and what are believed 
to be older but 1 i thologica 1 1 y similar Precambrian granitic 
augen and flaser gneisses in the core of the dome. Note 
counterclockwise drag folds in gneiss, believed to be a 
result of upthrusting of the gneissic core of the dome. 
Proceed easterly on Rt. 30 through broad zone of granitic 
gneisses to 

15.0 Townshend. Turn left off Rt. 30 onto Rt. 35 and proceed 
nor ther 1 y . 

15.^ STOP ^. Outc rops 1 ie across the field to t_he west and con - 
s i s t of magnet i te - bear i nq gran i te f laser gne i ss , be 1 i eved 
to have been the re lat i ve 1 y low - dens i ty " pi unger " account- 
i ng for the buoyant upward thrus t of the A thens dome. Con- 
tinue north on Rt. 35 through heterogeneous gneisses, some 
rusty weathering and containing coarse graphite flakes 
rather like the Washington gneiss described by Emerson in 
the Berkshi res . 

16.9 S impsonvi lie. 

18.4 Easy _t_o mi ss i ntersect ion . Bear left off Rt. 35 onto 
Grafton Road. 

18.6 For the next 0.2 miles, passing through a band of calc- 
silicate rocks, characterized by coarse graphite flakes 
and pyrrhotite, that strikes northeasterly through the 
core gneisses of the Athens dome at a large angle to the 
mantling strata. This discordance provides, perhaps, the 
best evidence to date that the core gneisses of the Athens 
dome lie unconformabl y beneath the mantling strata. 

18.8 Continue through banded, contorted, biotite gneisses of the 
core of the Athens dome. 

19-6 Top of grade. Bull Hill gneiss on dip slopes along east 
side of South Branch of Saxtons River to north. Valley 
probably owes its alignment to an easily eroded dolomite 
(observable at a number of localities on Rt. 35 north of 
Grafton) that separates albite schist of the Hoosac forma- 
tion on the west from the Bull Hill gneiss. 

20.3 Easy to m i s s turn . Turn sharply left onto single lane, 

steep dirt road (Acton Hill Road). Proceed through Hoosac 
forma t ion . 

20.6 Cross brook. 

20.9 East contact of game t-kyan i te- stauro 1 i te-paragon i te 
schist of Pinney Hollow formation in core of anticlinal 
portion of Ober Hill fold. Pass across Ober Hill fold. 

21.6 Intersection. Let lead car turn around before entering 

intersection. Then, one by one, each car should turn left, 
then bock up sufficiently far to make room for following 
cars to do same. Continue back down the Acton Hill Road, 
fo 1 lowi ng lead car , 



175 



21.8 Park your car as far off the road to the right as possible, 
STOP 6, exhi biting garnets wi th angu lar growth unconformi - 

t ies , i s on the 1 edges visible to the southwest of the road 
(Rosenfeld, 1968, p. 19^1"^ The rock is a garnet-staurol i te- 
paragoni te-muscovi te schist. Chloritoid and staurolite 
exist as an armored relict assemblage in the garnet. There 
is no chloritoid outside the garnet. The earlier garnet 
probably grew during the Taconic orogeny or possibly during 
an earlier orogeny. Proceed back toward Townshend-Graf ton 
Road. 
22.1 On the left are some remarkably fine counterclockwise drag 
folds, some of which have transcurrent "slip fractures" of 
similar shear sense about the same axis. These fractures 
provide evidence of the "lateness" of these folds. 

22.9 Townshend-Graf ton Road. Turn left and continue north. 
27.7 Grafton, a picturesque village in which some of the finer 

examples of old Yankee architecture have been restored and 
preserved by the liberal application of dollars. Turn left 
onto Rt. 121, passing successively through a rather complete 
section of units from the Hoosac formation to the rusty- 
weathering, graphitic schists of the middle Ordovician Cram 
Hill member of the Missisquoi formation. 
29.9 STOP 2- Westward di ppi ng beds of conglomeratic quartzi te 
and i nterbedded garnet - muscovite schi s t of Si 1 ur i an Shaw 
Mountai n forma t ion . These beds lie on the east limb of a 
syncline (Spring Hill syncline) whose axial surface dips to 
the west. This syncline is believed to be the detached (by 
megaboud i nage ) westward-opening, lower part of the Star Hill 
sigmoid (Figure 1, Section D-D'). It contains in its core 
a section of dense amphibolites that is thicker than usual 
within the Shaw Mountain formation. This dense mass, in 
the "keel" of the formerly westward opening fold, is believed 
to have "hinged" downward clockwise during the doming stage. 
Thus, the exposure at this stop is believed to be a relict 
of the short limb of the Star Hill sigmoid. In support of 
this interpretation is the sequence of rotations found in 
garnets within a schistose parting of Shaw Mountain quartz- 
i te a mile to the north--early clockwise, late counterclock- 
wise. "Unrotating" the late rotation at this exposure aligns 
the elongate pebbles in a west-southwest orientation, the 
direction of lateral extrusion. Some of the quartzite at 
this locality contains coexistent staurolite and chloritoid, 
a not rare assemblage in this unit. Turn around and return 
to 

32.1 Grafton on Rt. 121, continuing through the village across 
the Saxtons River and turning left onto 

32.2 Rt. 35. proceeding northerly along approximately the same 
s trat i graphic horizon that was followed south of Grafton. 
Bull Hill gneiss to east. 

33.9 Dolomite under albite schist of Hoosac formation on left. 
Leaving Athens dome; entering Chester dome. 



176 



36. k Enter Grafton Gulf. 

36.9 Leave Grafton, Windham County; enter Chester, Windsor County. 

37.0 Note pillar of dolomite supporting albite schist on left, 

dip slope of Bull Hill augen gneiss on right. 
37.5 Summit of Grafton Gulf. 

38.3 Leave Saxtons River Quadrangle; enter Ludlow Quadrangle. 
39.5 Chester. Turn right onto Rt. 103. 
40.9 Return to Saxtons River Quadrangle. 
42.3 Bull Hill gneiss on east limb of Chester dome. 
42.5 Enter town of Rockingham, Windham County. Crossing Hoosac 

format ion . 

42.7 Crossing from Pinney Hollow through intermediate units into 
Missisquoi formation. 

44.3 Easy to mi ss i ntersect ion . Turn sharp left off Rt. 103 onto 
dirt road with bridge over railroad tracks. 

44.4 "Vermont Beautiful" on left'. 

44.5 Covered bridge. 

44.8 Crossing Shaw Mountain format ion--not exposed near road. 

44.9 STOP 8. Ledges in woods north of road. S ieve texture gar - 
nets i n ca Icareous schi sts of lower Wa i ts R i ver format ion 
showi nq ear 1 y counterc lockwise rota t ion ( Event 1_; conspi cuous ) 
fo 1 lowed by late c lockwi se rotat ion ( Event II ; observed with 
difficulty ). Continue easterly. 

45-7 Optional STOP 8a. Ma i n zone of ca Icareous schi s ts wi th sub - 
ord i nate phy 1 1 i tes wi thin Wa i ts R i ver format i on . One of the 
best exposures of the Waits River formation in southern 
Vermont. Big sprays of zoisite. Isoclinal folding. Easily 
observed rotated garnets. Mafic dike with calcite pheno- 
crysts. Turn right across bridge and railroad tracks. 

46.0 Turn left onto Rt. 103. 

46.2 Turn right off Rt. 103 onto Pleasant Valley Road. Passing 

through heterogeneous rock types of Standing Pond formation, 
mostly mafic volcanics. 

47.1 Turn right off the Pleasant Valley Road onto single lane dirt 
road . 

47.2 Park cars and proceed northerly across field about 1,500 feet 
into woods just northwest of northwest corner of field to 
STOP ^ at contact between garnet i ferous phyllite of Waits 
River formation on west and coarse gar net i ferous schist of 
the Standing Pond formation containing sprays of hornblende 

( fasc icu 1 i t ic schist or "garbenschi efer" ) . Large garnets 
show a_ single 1 ar ge c I ockw i se rota t i on assoc i a ted with Event 
i, j_n contrast to those at Stop 8. A photograph of a rotated 
garnet from this locality appears as figure 14-6 in Rosenfeld, 
1968 (p. 195). Evidence of Event II at this locality appears 
only as gently northward plunging crinkles. For further dis- 
cussion of this locality, see Rosenfeld, 1970, p. 89. Return 
to Pleasant Valley Road by car. 

47.3 Turn right onto Pleasant Valley Road. 

48.7 Septum of Waits River-like calcareous schist and phyllite in 
Standing Pond formation. 



I 



177 



^8.8 Exposures of banded and massive amphibolites of Standing 
Pond formation near eastern contact with Gile Mountain 
formation. Clockwise drag folds. Road continues southerly 
along east side of Standing Pond formation. 

51.0 Intersection with Rt. 121. Continue east on Rt. 121. 

51.3 Villa ge of Sax tons River . Park cars. STOP 10 . The pur - 
pose of this s top i s to observe southv^ard pi unq i nq mi nor 
fo 1 ds i n the S tand i nq Pond format i on a I onq the ax i s of the 
upward c los i nq fo 1 d T an t i c 1 i ne ) of the Ascutney s i qmo i d . 
The axis at this horizon reappears to the south on the 
Guilford dome near the syntectonic Black Mountain granite 
in Dummerston (fig. 1). Folds with counter-rotating gar- 
nets on their limbs appear along the north side of the 
river, 0.3 miles to the west (Rosenfeld, 1970, p. 85-86). 
Turn westerly on Rt. 121. 

51.6 Bear right off Rt. 121 onto Pleasant Valley Road. 

56.2 Turn left off the Pleasant Valley Road onto Rt. 103. 

56.3 Turn right off Rt. 103 toward Brockways Mills, continuing 
across bridge past Stop 8a and to the right on paved road 
toward Springfield. 

57-5 Park. Proceed westerly across north end of field past 

small cottage to STOP 1 1 at contact between garnet i ferous 
phyllite of Waits River formation and "garbenschi efer" with 
large garnets. Thi s loca 1 i ty i s , perhaps , the best loca 1 i ty 
for seei nq evi dence of both Events l_ and II within a single 
rotated qarnet . A stereoscopic photograph of a rotated gar- 
net from this locality appears as figure ]k-3 in Rosenfeld, 
1968, p. 192. A discussion of the generation of the central 
surface of garnets at this locality is found in Rosenfeld, 
1970, p. kO. The trip ends at this locality. 

To get to Burlington, about 120 miles away, return to Rt. 
103, turn left, and get onto Interstate 91 North at Interchange 6. 
Turn left onto Interstate 89 at White River Junction. Interstate 
89 will take you to Burlington. 

References for Trip 7 

Bean, R. J., 1953. Relation of gravity anomalies to the geology of 

central Vermont and New Hampshire: Geol. Soc . America Bull., 
V. Gk, p. 509-538. 

Chang, P. H., Ern, E. H., Jr. and Thompson, J. B., Jr., 1965, Bedrock 
geology of the Woodstock Quadrangle, Vermont: Vermont Geol. 
Survey Bull., no. 29, 65 P- 

Doll, C. G., Cady, W. M., Thompson, J. B., Jr., and Billings, M. P., 
compi 1 ers and ed i tors , 1961, Centennial geologic map of 
Vermont: Montpelier, Vermont. Vermont Geol. Survey, scale 
1 :250,000. 



178 



Rosenfeld, J. L., I968, Garnet rotations due to the major Paleozoic 
deformations in southeast Vermont, p. 185-202 \_n Zen, E., 
White, W. S., Hadley, J. B., and Thompson, J. B., Edi tors , 
Studies of Appalachian Geology: Northern and Maritime: 
New York, Wi 1 ey-Intersc i ence Publishers. 

1970, Rotated garnets in metamorphic rocks: Geol. Soc . 



America, Special Paper 129, 105 p 

Skehan, J. W., S. J., 1961, The Green Mountain ant ic 1 i nor i um in 
the vicinity of Wilmington and V/oodford Vermont: Vermont 
Development Department, Montpelier, Vermont, Bull. No. 1 7i 
159 p. 

Figures 1 and 2 and Table 1, modified from figures 1^-1 and 
]h-5, respectively, and Table 1^-1 in Rosenfeld, I968, are repro- 
duced with the permission of John Wiley and Sons, Inc., holder of 
the copyr i ght . 



179 



Trip B-8 

STRATIGRAPHIC AND STRUCTURAL RELATIONSHIPS 
ACROSS THE GREEN MOUNTAIN ANTICLINORIUM 
IN NORTHCENTRAL VERMONT 



by 

Arden L. Albee 
Division of Geological and Planetary Sciences 
California Institute of Technology 
(Contribution Number 2161) 

Introduction 

This road log provides a guide for a field trip which extends 
from East Georgia to Hardwick, Vermont, along the Lamoille River. 
The stops were chosen to provide some understanding of the strati- 
graphic and structural relationships of the Cambrian and Ordovician 
rocks on both flanks of the Green Mountain anticlinorium and of the 
problems involved in the correlation of these rocks across the 
crest of the anticlinorium. 

Geologic mapping in this area preceded the compilation of the 
Geologic Map of Vermont (1961) ; the sketch map indicates only the 
route and major stops, and the State Geologic Map will serve as the 
basic map reference for this trip. The geologic reports on the 
four quadrangles involved have all been published: Milton quadran- 
gle (Stone and Dennis, 1964); Mt. Mansfield quadrangle (Christman, 
1959); Hyde Park quadrangle (Albee, 1957); Hardwick quadrangle 
(Konig and Dennis, 1964). In addition, Osberg (1969) gives a con- 
cise summary of the geology of this area and a reinterpretation of 
the patterns on the State Geologic Map. Albee (1968) describes the 
metamorphic zoning in northern Vermont. Since these reports are 
readily available, this road log will contain few details but will 
emphasize the need for additional detailed mapping in several areas 
to solve certain critical correlation and structural problems. 

The Green Mountain anticlinorium extends the full length of 
Vermont. Sequences on both its eastern and western flanks are rath- 
er uniform so that individual formations can be traced from Massa- 
chusetts, through Vermont, and some distance into Quebec. Rapid 
east-west facies changes, extensive unconformities, and thrust 
faults of unknown extent have been utilized in the correlation of 
these two sequences, but there is no generally accepted detailed 
correlation of the lower Paleozoic (pre-Shaw Mountain) units. 

In the absence of fossils, correlation can be attempted only 
by relating detailed lithologic characteristics and sequences or by 
tracing units along strike to points where they "bridge" the Green 
Mountain anticlinorium in an axial depression. The correlation on 



180 



the State Geologic Map of the Ottauquechee Formation with the 
Sweetsburg Formation and its upper Cambrian age assignment are 
based upon tracing units across such a "bridge" near the St. Fran- 
cis River about 50 miles north of the International Boundary (Cady, 
1960, p. 542, 548-549). The series of axial synclines which are 
crossed on this field trip offers another possible bridge for a 
more detailed east-west correlation of the pre-Ottauquechee units. 

Major structural units 

The major structural units and features to be crossed on 
this trip are described on the following pages from west to east. 

1) Hinesburg thrust — The Hinesburg thrust marks the east- 
ern limit of the Cambrian and Ordovician carbonate-quartzite as- 
semblage, which is relatively unmetamorphosed and which includes 
distinctive and fossiliferous strata. 

2) Georgia Mountain anticline and syncline — In these south- 
plunging folds the Dunham Dolomite (ed) and Cheshire Quartzite (Sc) , 
which are dated units of the carbonate-quartzite assemblage, over- 
lie a sequence consisting of the Fairfield Pond phyllite (Sufp) , 
White Brook dolomite (6uw) , Pinnacle graywacke (ep) , and Tibbit 
Hill volcanics (Spt) . (Descriptive lithologic names are used here ; 
formal usage is shown on the State Geologic Map.) Within this 

area the Tibbit Hill volcanics are the oldest rocks exposed, but 
they are probably interbedded with Pinnacle graywacke. 

3) Enosburg Falls anticline — The State Geologic Map shows 
a very complex pattern between the Pinnacle graywacke, the Tibbit 
Hill volcanics, and the Underhill phyllite. This complexity is 
due in part to folding, but much of it is due to lateral sedimen- 
tary intertonguing of these three units (see cross section A-A' of 
the State Geologic Map) . 

4) Cambridge-Richford syncline — The Underhill schist, a 
silvery-green, white mica-chlorite phyllite or schist, occupies 
most of this area. The Underhill schist is bordered to the west by, 
and probably generally overlies, the Pinnacle graywacke, but it 
also intertongues with it. Similarly, the Underhill schist is 
bordered to the east by, probably generally overlies, and in part 
intertongues with albite schist, which is mostly shown as Hazens 
Notch Formation (6h) on the State Geologic Map. This syncline al- 
so contains several distinctive rock types including greenstone 
(Gug and Gup) , limestone (Suw) , and graphitic phyllite and slate 
(Sue, es) whose detailed distributions are unknown. 

5) Axial anticline of the Green Mountain arch — The actual 
crest of the anticlinal arch is within rather coarse-grained por- 
phyroblastic albite schist, both graphitic and non-graphitic, with 



181 



minor laminated quartzite interbeds . These grade eastward and up- 
ward into graphitic schist and quartzite with much less prominent 
albite . 

6) Foot Brook syncline -- A shiny-green, paragonite- and 
chloritoid- bearing schist occurs in the core of the Foot Brook 
syncline. On the State Geologic Map this unit (6ufb) is shown as 
a facies tongue of the Underhill Formation, but it also has been 
tentatively correlated with the Stowe Formation (Ss) to the east 
(Albee, 1957 a, b) . 

7) Eastern limit of the Green Mountain anticlinorium — East 
of the Foot Brook syncline is a generally homoclinal sequence of 
units - the Hazen's Notch (eh), the Ottauquechee (So), the Stowe 
(oes) , the Umbrella Hill (OGu) , the Moretown (0mm), the Shaw Moun- 
tain (Ss) , the Northfield (DSn) , and the Waits River (Dw). The 
pattern on the State Geologic Map indicates the existence of folds, 
most of them subparallel to the Green Mountain anticlinorium. The 
largest of these folds is the Worchester Mountain anticline within 
the Stowe Formation. The base of the Shaw Mountains marks a major 
unconformity which has been traced the entire length of Vermont. 

Correlation across the axial anticline 

The correlation of the Ottauquechee Formation on the east 
limb of the Green Mountain anticlinorium with Cambrian units west 
of the Hinesburg thrust is well established, but it is not clear 
whether the Ottauquechee Formation or units above it occur in the 
Foot Brook and Cambridge-Richford synclines . The pattern of units 
between the Hinesburg thrust and the Ottauquechee band on the east 
limb of the Green Mountain anticlinorium is explained on the State 
Geologic Map by a combination of folding and of sedimentary and 
metamorphic facies changes which involve only pre-Ottauquechee un- 
its. An alternative possibility (Albee, 1957 a,b) is that the 
shiny schist in the Foot Brook syncline (Sufb) correlates with the 
Stowe Formation, that the underlying greenstone (6hg) with assoc- 
iated serpentinite correlates with the Belvidere Mountain amphibol- 
ite (Shb) , and that the intervening graphitic schist correlates 
with the Ottauquechee Formation, is continuous around the shiny 
schist, and extends northward into the area of the Ottauquechee 
Formation within a syncline south of Jay Peak (see State Geologic 
Map) . It is also possible that the Ottauquechee Formation and 
higher units are present in the Cambridge-Richford syncline. The 
two bands of greenstone (6ug and eup) may face each other across a 
syncline, with the Ottauquechee Formation lying above and between 
them, and correlate with the Belvidere Mountain amphibolite (Shb) . 
Alternatively, the graphitic phyllite (Sue) and black limestone 
(euw) near North Cambridge may correlate with the Ottauquechee 
Formation. Such an interpretation is based in part on a general- 
ized correlation of the albite schists of the axial region with 



182 



the Pinnacle graywacke . These suggestions do not deny extensive 
sedimentary facies changes such as are indicated by the State 
Geologic Map and would in fact require extensive facies changes. 
I simply wish to emphasize the need and importance of additional, 
very-detailed mapping and tracing of units within the axial syn- 
clines north and south of the Lamoille River. 

Minor structural features 

The axial anticline of the Green Mountain anticlinorium in 
northern Vermont is an arch of a well-developed schistosity. 
This schistosity is subparallel to bedding but is transverse to 
bedding in small folds with nearly east-west axes which are sub- 
normal to the axis of the arch. The schistosity, bedding, and 
east-west folds are folded about nearly-horizontal, north-south 
fold axes which parallel the axis of the Green Mountain anticlin- 
orium, and they are cut by a steep slip cleavage closely associ- 
ated with the "Green Mountain" crinkles and folds. Within the 
axial region the relative time relations are consistent and well- 
displayed. To the west the schistosity steepens and the dominant 
foliation is a schistosity roughly axial planar to the major folds. 
This steep schistosity dominates in the phyllites within the Cam- 
bridge-Richford syncline and the Enosburg Falls anticline, and the 
bedding is sufficiently disrupted as to provide very little obvi- 
ous guidance on the nature of the major folds in this area. The 
early east-west folds are rarely observable. Eastward from the 
axial region the schistosity also steepens; most outcrops contain 
steeply-plunging, fragmented folds, typically with a right-handed 
pattern. Nearly-horizontal, north-south folds are rarely observ- 
ed in individual outcrops although they dominate the pattern of 
the major units. Transposition schistosity is common, and the bed- 
ding trend in individual outcrops within thin distinctive units is 
independent of the trend of the unit. Only in greenstone, amphi- 
bolite, and quartzite is a true bedding schistosity preserved over 
any distance. In the crest of the Worchestor Mountain anticlinor- 
ium, amphibolite with nearly horizontal foliation is overlain by 
schist with nearly vertical schistosity. 

In the easternmost part of the area to be covered by this 
trip, a steeply dipping, north-trending schistosity dominates; but 
two sets of folds subnormal to each other may be observed in some 
outcrops. The steep foliation is transected by a rather widely 
spaced cleavage which may be related to the doming in eastern Ver- 
mont. Konig and Dennis (1964, p. 43) infer from outcrops near El- 
igo Pond, which will be seen on this trip, that "...Green Mountain 
cleavage appeared to displace doming cleavage..." Albee (1968, 
p. 331) suggests that "...most of the deformational and metamorph- 
ic features in the rocks in northwestern Vermont along the Green 
Mountain anticlinorium are pre-Silurian , probably middle Ordovician." 
A detailed study of the minor structural features on either side of 
the unconformable base of the Shaw Mountain Formation would help to 



183 



resolve this problem but is made difficult by the generally poor 
outcrop in this horizon and the differing competency of the rocks. 

Metcunorphism 

Most of northwestern Vermont lies outside the garnet zone 
within the biotite-chloritoid zone of metamorphism (see State Geol- 
ogic Map; Albee , 1968). Higher grade rocks occur in elongate areas 
associated with the crests of the Green Mountain and Worchester 
Mountain anticlinoria and throughout much of northeastern Vermont. 
The route of this trip lies to the north of the garnet zone rocks 
in the Green Mountain anticlinorium, passes through the garnet and 
kyanite zone rocks in the Worchester Mountain anticlinorium, and 
extends into the garnet zone rocks of eastern Vermont. The high- 
er grade rocks in the Worchester Mountains are extensively retro- 
graded, and Albee (1968) has discussed evidence suggesting that 
the higher grade metamorphism is pre-Silurian and that the retro- 
gradation occurred during Middle Devonian metamorphism responsible 
for the higher grade rocks in eastern Vermont. 

References cited 

Albee, A. L. (1957a) Bedrock geology of the Hyde Park quadrangle, 
Vermont: U. S. Geol. Survey, GQ-102. 

Albee, A. L. (1957b) Geology of the Hyde Park quadrangle, Vermont: 
Doctoral Thesis, Harvard University. 

Albee, A. L. (1968) Metamorphic zones in northern Vermont: Stud - 
ies in Appalachian Geology - Northern and Maritime , eds . Had- 
ley, Thompson, White, and Zen, Interscience , p. 329-342. 

Cady, W. M. (1960) Stratigraphic and geotectonic relationships in 
northern Vermont and southern Quebec: Geol. Soc. America Bull. 
71, p. 531-576. 

Christman, R. A. (1959) Geology of the Mt. Mansfield quadrangle, 
Vermont: Vermont Geological Survey, Bull. 12, 75 p. 

Doll, C. G. , Cady, W. M. , Thompson, J. B. , Jr. and Billings, M. P., 
compilers and editors (1961) Centennial geologic map of Vermont: 
Vermont Geological Survey, Montpelier, scale 1:250,000. 

Konig, R. H. and Dennis, J. G. (1964) The geology of the Hardwick 
area, Vermont: Vermont Geological Survey, Bull. 24, 57 p. 

Osberg, P. H. (1969) Lower Paleozoic stratigraphy and structural 
geology. Green Mountain - Sutton Mountain anticlinorium, Vermont 
and southern Quebec: North Atlantic - Geology and Continental 
Drift, Am. Assoc. Petroleum Geol. Memoir 12, p. 687-700. 



im 




185 



stone, S. W. and Dennis, J. G. (1964) The geology of the Milton 
quadrangle, Vermont: Vermont Geological Survey, Bull. 26, 
79 p. 

Road Log 

Most of the stops described in this road log could be visit- 
ed in one day by a small group, but a larger group would have to 
omit some stops. The choice of stops for the NEIGC trip will de- 
pend upon the weather and the size and interests of the group. The 
log is divided into segments or legs and the oddometer readings are 
reset at the start of each leg. The log has been written to be 
used in conjunction with the State Geologic Map, and no other maps 
are necessary. Only the general route and major stops are shown on 
the route map. 

Start Enter 1-89 at exit 14, just east of the UVM campus and 

proceed north to the East Georgia exit. The route crosses 
Cambrian units of the Champlain Valley carbonate-quartzite 
sequence . 

Leg A Leave 1-89 at East Georgia exit, 17.6 miles north of Burl- 
0.0 ington, and proceed south on US-7. 

0.3 Y-intersection; proceed southeast (left) on Vt-104A. 

1.3 Georgia Mountain, directly ahead, consists of Cheshire 

Quartzite (ec) and lies just east of the Hinesburg thrust. 

1.9 Large outcrop of Dunham Dolomite (6d) on left. 

2.0 Caution - one-way railroad underpass. The overpass is 
located on the trace of the Hinesburg thrust. 

2.2 Outcrop of dark-colored Cheshire Quartzite on left. For 
the next several miles the route crosses a south -plunging 
anticline and syncline (see State Geologic Map) in which 
the Dunham Dolomite (Sd) , the Cheshire Quartzite (Sc) , 
the Fairfield Pond (eu-Sp) and White Brook Dolomite mem- 
bers (euw) of the Underhill Formation, the Pinnacle Form- 
ation (ep) , and the Tibbet Hill volcanic member (6pt) of 
the Pinnacle Formation occur in their "normal" strati- 
graphic sequence. 

4.0 Large roche moutonnee of Cheshire Quartzite (Sc) . The 
bedding dips about 4 5° east, but the dominant foliation 
is nearly vertical. 

4.8 Y- junction with Vt-104; proceed south (right). 

4.9 Road cut on left in silvery-green phyllite, typical of 
Fairfield Pond Member (Sufp) . 



186 



5.1 For next nine miles the trip crosses graywacke (Sp) and 

volcanic (Spt) units of the Pinnacle Formation within the 
Enosburg Falls anticlinorium. The peculiar map patterns 
are inferred to be due both to folding and intertonguing 
relations. 

5.5 Fairfax Village; continue on Vt-10 4 across the Lamoille 
River. 

7.1 Y-junction; proceed east (left) on Vt-104. 

8.1 Stop A-1 - Fairfax Falls 

Caution - restricted visibility. Parking for 8-10 cars 
is available on left side of road. 

Large road cuts in massive graywacke of the Pinnacle Form- 
ation (Sp) . Although biotite is present, clastic grains 
are evident and clasts up to 2 inches are present. The 
dominant foliation is a schistosity dipping steeply east; 
bedding is difficult to discern in such massive beds. 

13.5 Junction - continue east on Vt-15. Sterling Mountain, dir- 
ectly ahead, is in the core of the Green Mountain anticlin- 
orium. 

14.1 Cambridge village. 

14.5 "Wrong-way Bridge" over the Lamoille River. Local residents 
claim the engineers read the plans incorrectly with north 
and south reversed. 

Leg B 
0.0 Turn east (right) at north end of "Wrong-way Bridge". 

0.5 Stop B-1 - Room for 8 cars on north side of road with clear 
visibility. 

Typical silvery-green schist of the Underhill Formation (Su) 
is exposed in road cuts on the south side of the road. The 
dominant foliation is a near-vertical schistosity, trans- 
verse to quartz lenses and layers which form steeply south- 
plunging, right-handed folds. Flat-surfaced natural out- 
crops occur about 200 feet east on the north side of the 
road. 

1.8 Bridge over Lamoille River. Continue straight. 

2.0 Intersection in center of Jef fersonville. On the south 

side of the road, a war memorial has been carved in a large, 
complexly-folded outcrop of Underhill schist. The curved 
face and steps provide a spectacular exhibition in three- 
dimensions of complex minor folds with associated slip clea- 
vage. 



187 



2.3 Junction of Vt-15 and Vt-10 8-109. Proceed north across 
bridge. 

2.4 Stop B-2 - Parking on east side for 10 cars. 

The field northwest of the bridge contains excellent out- 
crops of silvery-green Underhill schist (Gu) , which ex- 
hibits considerable textural variation. 

2.7 Junction; turn east (right) on Vt-109. 

Leg C 
0.0 Proceed north (left) from "Wrong-way Bridge" on blacktop 
road. 

2.9 Road triangle with cluster of houses; turn east (right) on 
gravel road. Note that this intersection is about a mile 
west of the road shown on the State Geologic Map. 

3.2 Stop C-1 - Park at top of hill. 

Outcrops of typical Tibbit Hill volcanic rocks (Epth) occur 
among the trees south of the road. These rocks are amphi- 
bolitic greenstones and contain coarse-amphibole , partially 
altered to actinolite and chlorite. 

4.0 Turn north (left) on gravel road. 

4.4 North Cambridge. Turn east (right) on gravel road. 

4.8 Outcrop of Underhill schist on right. 

5.2 Stop C-2 - Parking for about 6 cars on the right side along 
the turn; keep a flagman cihead. 

These outcrops include graphitic schist, quartzite, and lime- 
stone which are shown on the State Geologic Map as members 
(6uc and Guw) of the Underhill Formation within the core of 
the Cambridge-Richford syncline. On a lithologic basis it 
is conceivable that these rocks are correlatives of the Ot- 
tauquechee Formation (So) . 

6.2 Turn south (right) on Vt-108. 

8.2 Junction with Vt-109. Stop B-2, which is 0.3 miles south, 
has excellent outcrops of silvery-green Underhill schist 
(Su) . 

Leg D 
0.0 Junction of Vt-108 and Vt-109. Proceed east on Vt-109. 

0.9 Stop D-1 - Excellent road cut but no parking available for 
0.2 miles. 

Quartc-muscovite-chlorite schist characterized by abundant 
albite porphyroblasts and containing graphitic interbeds. 



188 



3.6 



3.9 
5.9 



6.8 



The west-dipping schistosity has nearly-horizontal, north- 
trending crinkles and transects down-dip plunging tight 
folds. Such features will be seen in detail at the next 
stops. 

The greenstone lense shown on the State Geologic Map (ehg) 
has been traced northward into the greenstone unit (Sup) 
and into Quebec. Hence, the pattern shown on the State 
Geologic Map is known to be incorrect in detail, but the 
correct pattern is not known. 

Junction - turn east (sharp right) off of Vt-109. 

Large outcrop of massive, coarse-grained albite gneiss on 
the left. The eastward dip indicates its position just 
east of the crest of the Green Mountain axial anticline. 
Large open "Green Mountain" folds in large outcrops are 
visible from the road for the next several miles. 

Stop D-2 - Parking for 8-10 cars on right side. Drivers 
should look at this outcrop and then move on 0.5 mile to 
park on a rock point on the right side of the road. Park 
two cars abreast to allow room for 7 cars. 

This series of outcrops includes graphitic and nongraphi- 
tic albite schist and gneiss as well as thin gray quart- 
zites that display quite remarkable contortions. These 
rocks are typical of the Hazens Notch Formation near the 
crest of the anticlinorium where porphyroblastic albite 
is abundant. Note that some albite porphyroblasts are 
black due to included graphite, although little graphite 
remains in the matrix. Garnet crystals also occur within 
albite porphyroblasts, although no garnet occurs in the 
matrix of the schist. 



In these outcrops a rock face subparallel to the road ap- 
pears to show a bedding schistosity dipping about 45° east 
and cut by a near-vertical slip cleavage associated with a 
near-horizontal crinkle and open "Green Mountain" folds. 
However, rock faces sub-normal to the road show that the 
apparent bedding schistosity is parallel to the long limbs 
and axial planes of tight, down-dip plunging folds and act- 
ually transects bedding in the crests of these folds. 

The time relationships can be discerned throughout these 
outcrops, but they are especially well shown at the second 
parking area on the cliff between the parking area and the 
river. The rock projection cibout 15 feet west of the oak 
tree is the crest of a "Green Mountain" fold, which plunges 
eUaout 10 • south. Crinkle axes parallel the larger fold ax- 
is. On both sides of the rock projection is a tight fold 



189 



in a gray qiiartzite layer. The fold axin ia aubnormal to 
that of the north-trendinq "Grraen Mountain" fold, panaofi 
entirely through the rock projection, and has boon foldod 
by the "Green Mountain" fold. This tlmn rolationnhip in 
consistently shown throughout the axial area of the Groon 
Mountain anticlinorium. 

7.7 Stop D-3 - Parking for 20 cars. 

Similar relationships to that at the last atop are well 
displayed in a 1000 foot series of road cuts. Tho rocks 
are similar, but gray quartzitos are more abundant. 

8.3 Junction; turn east (left on Vt-15.) 

The wooded ridge to the northeast has good outcrops of 
schist of the Foot Brook syncline (eufb) . It is a highly- 
aluminous schist, commonly containing chloritoid, and has 
been variously correlated with both the Underbill Forma- 
tion (eu) and the Stowe Formation (OSs). 

Gravel road to north. 



3. 


3 


Leq 


E 


0. 





1. 


4 



Proceed north on gravel road. 

Stop E-1 

Silvery-green schist of the Foot Brook syncline (Sufb) is 

exposed in the stream just north of the road. 

2.8 Return to Vt-15. 

Leg F 
0.0 Proceed east on Vt-15. 

0.5 Stop F-1 - Parking for 8 cars on right side of road beyond 
outcrop. 

This outcrop is quite typical of those that might be seen 
in the Hazens Notch Forroation (6h) for the next 6 miles 
eastwcurd along the highway. They consist predominantly of 
graphitic schist and quartzite with minor nongraphitic 
quartzose schist and typically display pronounced sulfidic 
weathering. The rocks are fine-grained and do not typical- 
ly contain biotite or porphyroblastic albite. The schist- 
osity is typically steep, north-trending, and subparallel 
to the long limbs of folds in the quartzite beds. Abun- 
dant steeply plunging folds occur in the quartzite beds 
auid in quartzose layers or pods in the schist. In this 
road cut it is possible to recognize "Green Mountain" folds, 
crinkles, and slip cleavage; but it is difficult to discern 
them in most natural outcrops. 

1-1 Johnson Village. 



190 



4.4 The outcrops along the road contain an assemblage of rock 
types and structural features similar to those seen at the 
last stop. 

5.8 Junction with Vt-100, continue east on Vt-15-100. 

6.1 End of Leg F at blacktop road on north side of highway just 
east of small restaurant. 

Leg G 
0.0 Turn north (left) on blacktop road. 

0.5 Y- junction, proceed east (right). 

1.1 Stop G-1 - Park along right side of road both east and west 
of Y-]unction. 

The large outcrop north of the road is in a narrow band of 
quartz-muscovite-chlorite-magnetite schist, (ehm) which oc- 
curs just below the Ottauquechee Formation (So) at the pos- 
ition of the Pinney Hollow Formation (Sph) . Its silver- 
green color is in marked contrast to the graphitic-sulfidic 
rocks above it and below it. Although it extends in a 
straight north-trending band for about 10 miles, it typical- 
ly contains very diverse bedding trends with steeo folds 
and transposition schistosity. These structures appear to 
be internal to the unit. Similar bands to the west (see 
State Geologic Map) may be different units or may represent 
repetition of this unit by folding. 

1.1 Proceed east (straight ahead). 

1.4 Proceed north (left) on gravel road. 

3.1 Proceed west (left) on blacktop road. 

3.2 Continue straight ahead. 

3.7 Stop G-2 - Park on right. No hammers please. 

The flat outcrop about 300 feet south of the road displays 
a wide variety of complex structural features reflecting 
the variation in competency of different lithologic types. 
The interbedded schist and quartzite in this outcrop is 
within the Ottauquechee Formation (So) but is not typical 
of that unit. 

4.1 Recross the ehm band at height of land. 

5.4 Return to Vt-100-15. 

Leg H 
0.0 Proceed east on Vt-100-15. 



191 



1.6 East (right) on Vt-100 toward Morrisville. 

2.6 Cross railroad tracks and turn east (left) into Morrisville. 

2.7 Cross bridge and turn south (right). 
2.9 Stoplight - turn east (left) on Vt-12. 

5.1 Turn south (right) on Elmore Mountain Road. 

5.4 Stop H-1 - Park on gravel road to east (left). 

Abundant flat outcrops of amphibolite of the Stowe Formation 
(oesg) . These outcrops with their gently-dipping foliation 
are part of a broad band of amphibolite that dips under and 
reappears on the east side of the kyanite-grade schist on 
Elmore Mountain. At their contact flat-lying amphibolite 
is overlain by a coarse-grained muscovite-garnet-kyanite 
schist with a near-vertical, north-trending schistosity and 
very poorly preserved bedding. These garnet and kyanite 
zone rocks in the Worchester Mountain anticline have been 
extensively retrograded at a time postdating the formation 
of the dominant schistosity and folds. 

Continue north on gravel road. 

5.8 Turn east (right) on Vt-12. Numerous outcrops of the flat- 
lying amphibolite can be observed along the road on the 
north side of Elmore Mountain. 

7.1 No room to park. Outcrops of coarse-grained schist of the 
Stowe Formation (OSs) containing garnet retrograded to 

7.6 chlorite. 

7.7 Stop H-2 - Elmore State Park. 

Outcrops of Stowe schist and amphibolite can be seen in the 
Upper Campground. Park at Campsite No. 5, drop about 20 
feet south into the small stream, and go upstream about 600 
feet to large outcrops of garnet-bearing schist. Small out- 
crops of amphibolite and a 15 foot glacial erratic of ser- 
pentinite may be seen downstream from the schist outcrop. 
A large outcrop of amphibolite is behind the rest room. 

7.8 End of Leg H, Elmore Village. 

Leg I Side trip to kyanite-zone schist of the Stowe Formation. 
0.0 Proceed south on Vt-12 from Elmore Village. 

1.1 Stop I-l - Parking on side road to right. 

Roadcut in compositionally-layered amphibolite of the Stowe 
Formation. 



192 



2.5 Outcrops of phyllite and "pinstripe" of Moretown member 
of Missisquoi Formation (0mm) . 

2.8 Stop 1-2 - Go west (right) on dirt road; the condition 

of this road varies greatly, but it is always high-cent- 
ered. May drive 0.5 mile west to edge of woods and park; 
then follow VN/ood road an additional 0.4 mile across two 
streams to a point about 300 feet west of the second 
stream. 

A prospect pit about 50 feet north of the wood road was 
dug for iron in a layer rich in ilmenite, kyanite , and 
chloritoid. In the area immediately north of the pit are 
good outcrops of kyanite-garnet-muscovite schist interbed- 
ded with coarse-grained garnet amphibolite. These rocks 
have undergone rather extensive retrogradation to aggre- 
gates of white mica, chloritoid, and chlorite. Return to 
Elmore Village. 

Leg J 
0.0 At Elmore Village turn east on gravel road. 

3.8 Bridge over Lamoille River. 

4.0 Stop J-1 - Turn east (right) on Vt-15 and park on right 

side. This outcroD of interbedded fine-grained quartzite 
and slate with biotite porphyroblasts is typical of the 
Moretown Member of the Missisquoi Formation (0mm) . The 
bedding dips about 75° east; there are almost no minor 
folds, but there is a slightly more steeply-dipping clea- 
vage. 



Proceed east on Vt-15. 

Wolcott Village. 

Bridge over Lamoille River. The abundant outcrops in the 
next mile are generally similar to those at the last stop. 

3.2 Stop K-1 - Ample parking on left side with good visibility, 
The covered bridge is the only one still being used by a 
railroad and is characterized by its full-length ventila- 
tor. It was rebuilt and strengthened several years ago 
with donations collected in a state-wide drive. 
The outcrop contains granulite, quartzite, and slate rath- 
er similar to that seen at the last stop; but a number of 
repetitions by larger folds are present. Both north-trend- 
ing horizontal fold axes and steep fold axes subnormal to 
the horizontal axes are abundant; these fold relationships 
are similar to those seen in the axial region of the Green 
Mountain anticlinorium. Such relationships are rarely ob- 



Lee 


1 K 











9 


1 


5 



193 



served in natural exposures. "Pinstripe" foliation has 
developed both parallel to and transverse to bedding. Gar- 
net occurs locally in this outcrop although it is some dis- 
tance west of the mapped garnet isograd. 

6.0 Junction with Vt-14 - End of Leg K. 

Leg L 
0.0 Proceed north on Vt-14 along a valley typical of those as- 
sociated with the Shaw Mountain and Northfield formations. 

4.9 Stop L-1 - Parking on left; south end of Eligo Pond. 

Garnet-biotite phyllite and calcareous phyllite of North- 
field Formation (D-Sn) . There are several sets of crink- 
les , but the dominant folds plunge about 20 °N 20 °E and 
are overturned to the east. 

6.2 Stop L-2 - Parking on left beyond outcrop. 

The readout contains green garnet phyllite of the Moretown 
Member (0mm) with gently north-plunging fold axes and crin- 
kles with an associated slip cleavage. East of the road 
opposite the parking area is a large outcrop of biotite 
granulite, possibly a metavolcanic, which is part of the 
Shaw Mountain Formation (Ss) . Several hundred feet further 
east in the trees is garnet-biotite phyllite of the North- 
field Formation (D-Sn) similar to that seen at the last 
stop. The same structural features appear to be present 
in all three units, but a freeway cut would be very useful 
right here. 

6.7 Large road cut in Northfield slate and quartzite with gent- 
ly north-plunging folds overturned to the east. Garnet in 
this outcrop has been retrograded. 

9.5 End of Leg L at blacktop road to west. 

Leg M 
0.0 Proceed west on blacktop road with directional sign point- 
ing to North Wolcott. 

0.4 Turn north (right) on gravel road at road triangle. 

2.0 Continue west (left) at Y- junction with old school house. 

5.1 Stop M-1 - Parking on left side of road at height of land. 
The most accessible outcrops are under the power line about 
75 feet north of the road. 

The Umbrella Hill conglomerate (Omu) crops out for about 
25 miles as a thin band between the Stowe Formation (OSs) 
and the Moretown Member (0mm) . It contains subrounded 
quartz clasts and angular red, gray, yellow, and green 



194 



I 



Leg ^ 
0,0 



slate clasts up t 
slate clasts are 
tosity of the mat 
unit contains chl 
as well as quartz 
plates and the qu 
ity. Quartz-kyan 
south of the road 
in the brush abou 



o 4 inches in a phyllitic matrix. The 
deformed into alignment with the schis- 
rix. Throughout its outcrop length the 
oritoid plates in both clasts and matrix 
-kyanite veins. Both the chloritoid 
artz-kyanite veins transect the schistos- 
ite veins are well exposed about 1000 feet 
, and several small veins occur in outcrops 
t 50 feet north of the power line. 



6.4 Directly ahead can be seen the old asbestos workings near 
the top of Belvidere Mountain and the newer quarries lower 
down on the northeast side. 

7.6 Outcrops on left are pebbly quartzite and schist of the Ot- 
tauquechee Formation (Go) . From here north this unit con- 
tains abundant pebbly beds and differs considerably from 
its appearance to the south. 

7.8 Junction with Vt-100; poor visibilitv, turn south (left). 

7.9 Eden Mills Village. Road to north (right) leads to the 
asbestos mines. 

9.5 Eden Corners. End of Leg M. Return to south via Vt-100 
and Vt-15, or return to Burlington via Vt-118. 



Eden Corners 



Proceed west on Vt-11! 



4,7 New road cuts contain graphitic and non-graphitic albite 

gneiss similar to that seen in the axial region at the 
5.7 Lamoille River and contain similar structural features. 

6.6 Junction Vt-109. Turn south (left) and follow Vt-109 for 
15 miles to rejoin Vt-15 and return to Burlington. 



195 



Trip B-9 

SUPERPOSED FOLDS AND STRUCTURAL CHRONOLOGY ALONG THE 
SOUTHEASTERN PART OF T}ffi HINESBURG SYNCLINORIUM 

by 

Richard Gillespie, Rolfe Stanley, 
Terry Frank, and Thelma Barton 
University of Vermont 

INTRODUCTION 

The regional geology of the Hinesburg synclinor- 
ium has been described by various authors; most notably 
Cady (19^5, I960, I969), Welby (I96I), Stone and Dennis 
(I96U), and Stanley (I969, and this volume). The Centen- 
nial Geologic Map of Vermont (Doll et. al., I96I) is a 
representation of the state of knowledge of the synclinor- 
ium up to the time of its publication. More recent work 
carried out by various persons at the University of 
Vermont has greatly added to the knowledge of the struc- 
tures and deformational history of the area. 

It is the intention of this paper to bring to- 
gether the attainments of the more recent work into an 
understandable and acceptable revision or alternate 
interpretation of the state geologic map, 

ACKNOWLEDGEMENTS 

Recent work in the southern portion of the 
Hinesburg synclinorium has been carried out by several 
students at the University of Vermont. Information con- 
cerning the northwestern sector of the study area is 
largely drawn from unpublished reports of John Pratt, 
Thelma Barton and Barbara Gilman. Information from the 
western portion is taken from reports by Terry Frank 
and Thelma Barton. The eastern half of the area was 
studied by this author in conjunction with the prepar- 
ation for a Master's Degree thesis at the University. 

REGIONAL GEOLOGIC SETTING 

For a brief account of the regional geologic 
setting the author refers you to Stanley and Sarkesian 
(Trip B-5) in this volume. 



^'-' 



Figure 1 







197 



EXPLANATION 



< 
(J 

^ Lower 

Q 
cr 

O 



BROWNELL MTN. PHYLLITE MBR. 
BASCOM FORMATION 
CUTTING DOLOMITE 
SHELBURNE FORMATION 







Upper 



CLARENDON SPRINGS DOLOMITE 
DANBY FORMATION 



• • • 4 

• • • <| 



cr 

cQ Middle (?) winooski dolomite 

n I nwpr UNDIFFERENTIATED CHESHIRE 

U Lower QUARTZITE AND UNDERHILL 

PHYLLITE 



Thrust fault, sawteeth on upper plate, Hinesburg fault 
Formation contact, accurate 
Fornnation contact, approximate 
S-2 cleavage Y" S-3 cleavage \ 



m 
ill 



^ 




^> 



\0 



S-1 bedding \i» 



198 

Figure 2 



V 

\ 



\ 



/ / 



/ / 
/ / 

/ / 



/ / 

\J If 



\ 

V 

I 

V 




GENERAL STRUCTURE MAP 







'f ; r-v^-' 



199 



STRATIGRAPHY 



The stratigraphy of the area is described in 
Table T and II in the paper by Stanley and Sarkesian in 
this volume (Trip B-5). Only the Winooski through the 
Bascom Formation in the Hinesburg area will be discussed 
here since recent mapping has concentrated on these units. 



Lower Cambrian 

Cheshire Quartz ite - Typical Cheshire is a massive, 
very thick bedded white quartzite. The lower part is brown- 
ish weathering and is quite argillaceous and less massive. 
East of the Hinesburg thrust, the contact with the Under- 
bill Formation is gradational and placed above the chlor- 
itic schists and phyllites and below the mottled gray 
argillaceous quartzites showing well developed slaty clea- 
vage. The author has not mapped the contact in the Hines- 
burg area, 

Dunham Dolomite - This formation is not present 
in the area of study but occurs extnsively to the south 
and west, 

Monkton Quartzite - This formation also does 
not appear in the study area but outcrops extensively to the 
west in the upper plate of the Champlain thrust. 

Middle Cambrian (?) 

Winooski Dolomite - The Winooski consists of 
light gray to buff weathering dolostone, being gray to 
light pink or buff on the fresh surface. Thin phyllitic 
or siliceous laminae is sharp and tends to be marked by 
a distinct physical break. This contact zone, consist- 
ing of a thin phyllitic limestone with a closely spaced 
cleavage parallel to the contact is similar in appear- 
ance to a fault contact. 



Upper Cambrian 

Danb y Formation - Beds of gray and brown cross- 
bedded sandstone interlayered with beds of dolostone 1 to 
2 feet thick are characteristic of the Danby Formation, 
The sandstones may be relatively pure massive white quartz- 
ite'i at some localities, A few thin layers of shale have 
also been observed near the top of the formation. In 
one locality (Stop #5)(; the basal Danby is an unusual 
boulder conglomerate made up of large blocks of sandstone, 



200 



dolostone, and quartzite in a sandy matrix. The atti- 
tude of bedding is more readily determined in the Danby 
than in the massive dolomites above and below. The con- 
tact with the overlying Clarendon Springs Dolomite appears 
to be gradational with the sandstones and interbedded 
dolostones of the Danby gradually giving way to the more 
dolomitic formation above. 

Clarendon Spring s Dolomite - The Clarendon 
Springs is a massive gray weathered dolostone, buff to 
gray on the fresh surface with a tendency to be coarsely 
crystalline. The most obvious feature of this unit is the 
presence of knots and segregations of quartz crystals 
standing out from the weathered surface. Some of the other 
dolostones in the section also show quartz knots but they 
are not as ubiquitous as in the Clarendon Springs, A 
few beds of calcareous sandstone stand out from weathered 
surfaces and are generally the only bedding indicator 
discernable in the monotonous dolostone section. Blue- 
black chert nodules are common near the top of the forma- 
tion. The contact with the overlying Shelburne Formation 
is gradational and marked by a zone of mixture of the two 
with patches of Shelburne in depressions surrounded by 
more resistant dolostone. 



Lower Ordovician 

Shelburne Formation - The Shelburne is a massive 
dove gray weathered limestone and pink to white marble 
streaked with buff dolomitic stringers. There are also a 
few beds of sandy phyllite present. The Shelburne Forma- 
tion is undoubtedly the most readily identifiable unit 
found in the Hinesburg area. The variety of rock types 
near the contact with the surrounding formations provides 
excellent structural markers of the several generations of 
folds in the area. The contact with the overlying Cutting 
Dolomite is usually sharp with sandy dolostone above and 
white marbles and gray limestones below. 

Stone and Dennis (1964, p, 51) state that in the 
Milton area the Cutting "lies with destinct disconformity 
on the underlying Shelburne," In the Mechanic sville area, 
near the thrust contact, the Cutting seems to be absent 
entirely from the section placing the Bascom Formation on 
the Shelburne Formation, This could be due to a strati- 
graphic pinchout of the Cutting which begins in the area 
of St, George, Vermont, The other explanation would be 
that the Bascom-Shelburne contact is a thrust contact, 
the Bascom being dragged up along the Hinesburg thrust. 



201 



Guttin g: Dolomite - The Cutting is a massive 
whitish to light gray weathering dolostone, dark gray- 
on the fresh surface with a tendency to be fine-grained. 
Large calcite crystals up to 1" across are common in 
some areas. The base of the formation is a thinly lam- 
inated cross-bedded, calcareous sandstone while the upper 
part contains black chert nodules. The contact with the 
overlying Bascom Formation was nowhere observed in the 
eastern half of the study area but Gady (19^5, p. 5^3) 
states that there is no "apparent stratigraphic break." 

Bascom Formation - This formation contains the 
widest variety of lithologies of any rocks in the Cambro- 
Ordovician section (Gady, 19^5i p. ^2). In the study 
area the Bascom is a blue-gray limestone with interbeds 
of buff to orange weathered dolomite and gray calcareous 
sandstone. Phyllitic laminae can be found in some of 
the limestone layers. The formation forms the lower 
plate of the Hinesburg thrust at the Mechanicsville 
exposure and appears discontinuously to the south. 

Gady has more recently divided the Bascom 
Formation into the Brownell IWountain Phyllite Member 
and the typical Bascom (see Doll,et. al,, I96I and Gady, 
i960, p. 539, footnote #7). According to Gady, the Brown- 
ell Mountain Phyllite is a calcareous phyllite in the 
upper part of the Bascom on the east limb of the Hines- 
burg synclinorium. During the course of recent field 
mapping a black calcareous phyllite has been found here 
and there along the Hinesburg thrust and in lens-shaped 
bodies on Brov/nell Mountain. V/here the contact can be 
1 occtted within a few feet the change frOm limr"*-^rn<= or 
do]oc;tcne to bla-:k phyllit*^ i? abrupt. Inte'^r.'^di^tp 
rcrk types be'*:'A-pcn the limestone typical of the Bascom 
and the black phyllite have not been recognized. Tv/o 
explanations are suggested for these relationships. 
First, the black phyllite may be a series of thrust 
s2 ivers or older shales dragged up along the sole of the 
thrust plate and intermingled with slivers of alloch- 
thonous Bascom carbonates. This interpretation was 
suggested by Gady (19^5t P. 567, 57^, and Plate 10) in 
which the phyllite was correlated with the Skeels Cor- 
ners Formation of Upper Cambrian age and formed the upper 
plate of the Muddy Brook thrust. Second, the black 
phyllite may be equivalent to the Hortonville and Walloom- 
sac Formations of Middle Ordovician age that unconform- 
ably overlie older rocks in western New England, Sub- 
sequent movement along the Hinesburg thrust has plucked 
the black phyllites and mixed them with the other carbon- 
ate slivers which are found at such places as Mechanics- 
ville near Hinesburg, 



202 



POSSIBLE UNCONFORMITIES 

Evidence from field mapping seems to indicate 
that the Winooski Dolomite-Danby Formation contact is 
an unconformity. The evidence has been previously men- 
tioned in the descriptions of the formations and is 
discussed under the description of Stop #5. 

Another area which suggests an unconformity is 
the area east of the cemetary near Mechanicsville. Here 
the nondescript dolostones of the Cutting appear to rest 
on the dolostones of the Clarendon Springs with the Shel- 
burne Formation notably absent, except for a small lens 
farther to the south. The contact between the two dolo- 
stones has not been directly identified but extensive 
exposure of the two formations makes it likely that the 
easily identified Shelburne occurs between them. The 
cause for the unconformity has not been determined. It 
may be a stratigraphic pinchout or a tectonic result of 
the nearby Hinesburg thrust j the Shelburne being tec- 
tonioally squeezed out between the more resistant dolo- 
stones or absent due to imbricate thrusting. 

The third area which suggests an unconformity 
is near the Mechanicsville exposure of the Hinesburg 
thrust, Sandy limestones of the Bascom Formation appear 
to rest unconformably on the Shelburne Formation with 
the Cutting absent. The actual contact of the two forma- 
tions is covered by recent stream deposits. No boulders 
of dolostone could be found in the stream bed as might 
be expected if the Cutting were present. The presence 
of the Cutting is even somewhat doubtful in the area of 
the anticline depicted on Figure 1 near St. George to 
the northwest. Outcrops of Bascom and Shelburne occur 
quite close to each other there with no Cutting evident. 
Two explanations are possible for this unconformity. 
First, the Cutting is stratigraphically thinned and 
disappears to the northwest not reappearing from under 
the thrust at Mechanicsville. Second, the Bascom- 
Shelburne contact is a thrust contact at Mechanicsville, 
the Bascom being a thrust sliver dragged up along the sole 
of the thrust. However, if this were the case, one would 
expect a change in the bedding and first generation 
cleavage across the contact. This does not appear to be 
the case but does not entirely rule out the thrust hypo- 
thesis. 



METAMORPHISM 

A petrographic study of the Brownell Mountain 
Phyllite, the Fairfield Pond Member of the Underbill Form- 
ation as well as a thin phyllite in the Shelburne Formation 



Figure 3 






c 



STOP MAP 

SCALE 



ROUTE 
STOPS 



5mi 

n 



20<f 



was under taken to determine similarities and differences 
between the units. This was carried out with the intent 
of elucidating the modes of deformation, def ormational 
histories, and grade of metamorphism relationships that 
may occur across the Hinesburg thrust fault. 

Doll, et. al. (1961) describe the Fairfield 
Pond Member as a "greenish quartzite schist (quartz - 
sericite - albite - chlorite - biotite) and a sericite - 
quartz - chlorite phyllite," No biotite was observed in 
thin-sections from the Mechr.nicsville area in the Under- 
bill Formation so it is not known at this time whether 
the Fairfield Pond Member reached the biotite isograd 
in this area. The phyllites of the lower plate were 
much more graphitic with the dominant phyllosilicate 
being very fine-grained muscovite. X-ray analysis is 
needed in order to more definitively locate the isograds. 
This will be undertaken in the near future. 



FIELD TRIP STOPS 

Stop 1 - Cheshire Quartzite on Rt. 116 north of Hinesburg , 
The first location is along Rt. II6 approximately 1 1/2 
miles north of the village of Hinesburg, It is in the 
Cheshire Quartzite which forms the upper plate of the 
Hinesburg thrust in this area. At least two fold gener- 
ations are present in this outcrop and possibly a third. 
The first generation slaty cleavage has been cut by a 
well developed spaced slip cleavage. The lineation 
formed by the intersection of the two cleavages may be 
systematically folded on a broader scale but lack of 
outcrop showing the lineation has not permitted detailed 
analysis. The Hinesburg thrust lies just to the west 
of the outcrop under recent deposits. 

Stop 2 - Hinesburg thrust at Mechanicsville . This stop 
is the only exposure of the Hinesburg thrust in the 
Hinesburg synclinorium and is probably the finest in 
western Vermont. Here, the argillaceous Lower Cambrian 
Cheshire Quartzite rests upon the Lower Ordovician lime- 
stones and dolostones of the Bascom Formation. In at 
least two small areas the black phyllites, previously 
assigned to the Brownell Mountain Phyllite, can be seen 
below the thrust contact. The limestones of the lower 
plate and the argillaceous quartzites of the upper plate 
have been folded into minor northeast and southwest 
plunging anticlines and synclines. An exposure of the 
Brownell Mountain Phyllite just to the west of the thrust 
shows clear evidence for two generations of deformation 
with the development of a slip cleavage deforming the 
original slaty cleavage. 



1 



205 

Figure 4 







Fi^.ure 4 Lov;er hemisphere equal area projections of structures 
east of Rt. 116 in the town of Hinesburg, Vermont. A) poles 
to first generation closely spaced cleavage in Cheshire 
Q,uartzite (•) and second generation slip cleavage (o) at 
Stop 1. B) 78 poles to first generation closely spaced 
cleavage in Shelhurne, Bascom, and Bro\vnell Mtn. Phyllite 
Formations (•)• O) 22 lineations in 3helburne Formation 
formed by the Intersection of bedding and first generation 
cleavage (•). D) poles to axial surfaces of folds in the 
Cheshire, ohelburne, Bascom, and Brovmell Mtn. Phyllite 
Formations at Mechanicsville (•) and hinges of above folds (o). 



206 



A short traverse down a nearby stream crosses 
lower Bascom sandy limestones and marbles of the Shel- 
burne Formation. The intervening Cutting Dolomite, if 
present in this area, is very thin and not exposed due 
to recent cover (see above under Possible Unconformities), 
Doloraitic stringers in the white marbles give some indica- 
tion of the bedding as well as display minor folds along 
the older cleavage. 

Stop 2 - Ketc ham's Pasture , East . As shown on the accom- 
panying map and profile section, Figures 6 and 7, Ket- 
cham's Pasture consists of an eastern portion, made up 
of an isoclinal anticline with an axial surface dipping 
steeply to the west, and a western series of more com- 
plexly deformed folds. Stop 3 is located in the transi- 
tional zone between the Shelburne and the Cutting Forma- 
tions. The transitional zone consists of interbedded 
buff to tan, extensively jointed dolostones and blue- 
gray limestones with small sandy and shaly layers. 
Boudinage commonly accompanies the deformation of this 
unit and is displayed in an exposure approximately 
1500 feet north of this stop. 

At Stop 3» sandy layers in the limestone define 
bedding {S-^) , Folding of bedding, as shown by equal area 
stereonet projection (Figure 8A), produces a hinge orien- 
tation of N9E at 7W. This F^ folding produces an axial 
surface cleavage S2, S2 is well-developed and is recog- 
nized as a closely spaced (commonly less than one-six- 
teenth inch) cleavage transecting bedding. Figure 8B 
shows the orientation of the S2 cleavage plane, N7E at 
29E, and the Sg axial surface, NI6W at 32E. A second, 
younger fold generation is also recognized. Fg folds 
deform S2 and produce a slip cleavage S^. S3 is orient- 
ed at approximately the same strike as Sp ^^^ ^I't ^ steep- 
er dip. As shown in Figure 8D, the So cleavage plane is 
NIOE at 80E and the S^ axial surface Is NI3E at 6^E. 
Fp hinge measurements are scattered and are shown in 
Figure 8E. 

At the southernmost outcrop at Stop 3, the 
two fold generations are well expressed. Hinges of both 
folds are present and refolding of S2 cleavage is evident, 
producing a weakly developed S^ cleavage. I50 feet to 
the north, a large antiformal F2 hinge is associated with 
folding of the well-developed S^ cleavage (Figure 5A). 
Poorly developed S^ cleavage is oriented N6OE at ^8S 
at this outcrop. Further to the north, a series of F-^^ 
folds are observed, again in the sandy layers in the 
limestone (Figure5B). Fj_ hinge measurements from this 
outcrop are included in Figre 8C and define an axial 
surface oriented N5E at I5E and suggest a slip line of 
N80E at 15s. 



207 



Stop ^ - Ketc ham's Parvture, West . At this stop in the 
western half of Ketcham's Pasture, F2 deformation is 
less pronounced. Inside the gate, immediately to the 
west of the Ketcham residence, both fold generations 
can be seen. Figure 5*^ shows Fp folds deforming S2 
cleavage at this location. IO06 feet to the northwest, 
however, at Stop 4, only the earlier fold generation is 
present. 

Stop 4 is located near the contact between the 
Shelburne Formation and the transitional zone. Bedding 
in the Shelburne is folded around a hinge oriented 
N65ii at 22s and the cleavage associated with this F-j, 
fold generation is not characteristic of the S2 cleavage 
observed elsewhere in the area. It is a widely spaced 
slip cleavage resembling the S-, cleavage at other local- 
ities and is oriented approximately N5bK at 5OS. Quartz 
filling of Sp cleavage planes is common. In Figure 5D, 
sandy layers in the limestone show crinkle folds and 
display the widely spaced S2 cleavage. 

Slightly to the west of the main cliff at Stop 
U a basic dike, oriented N75W at 7^S, intrudes the sedi- 
mentary sequence. It is typical of several such E-W 
striking, nearly vertical dikes found at Ketcham's 
Pasture and probably represents an event much younger 
than the most recent deformation at Ketcham's Pasture. 

Stop ^ - Winooski DoloTnite - Danb y Formation Contact . 
This stop is unusual in that it has never been reported 
in the literature. We will cross Middle Cambrian (?) 
Winooski Dolostone and view the contact with the Upper 
Cambrian Danby Formation. In this area, as well as in 
all other areas where the contact has been seen, a sharp 
break separates the two formations. In this locality, 
however, the lower Danby contains a local boulder conglom- 
erate; the large boulders being blocks of cross-bedded 
sandstone and quartzite and massive buff to brown dolo- 
stones set in a sandy matrix. 

Whether the Winooski is Middle Cambrian in_ 
age or actually Lower Cambrian has never been determined 
directly. The" complete absence of fossils has made it 
impossible to paleontologically date the formation in 
the Hinesburg area. In the St. Albans, Vermont, area, 
the Parker Formation underlies part of the Winooski 
there and has yielded Middle Cambrian fossils. There- 
fore, Stone and Dennis (1964) have assigned a Middle 
Cambrian age to the Winooski. Cady (19^5) has placed 
the Danby in the Upper Cambrian while Stone and Dennis 
have correlated the Danby with the Woods Corners Group 



208 



I 



Figure 5 Descriptions 



A. Large F antiform at Stop 3: The closely- 
spaced Fi cleavage has been gently folded by 
F2; the poorly developed, more widely-spaced 
F2 cleavage is mostly easily seen in the lower 
left of the photo. 

B. Tight F-j^ folds at the northern end of 
Stop 3: A thin dolostone bed in the other- 
wise massive marble reflects the tight Fj^ 
isoclinal folding. 

C. Fj^ and F2 folds by the gate NW of the 
farm house: The light-colored dolostone bed 
is gently folded by F-^ which is then refolded 
by F2 into tighter folds as seen in the lower 
left. 

D. F-j^ folds with quartz-filled cleavage 
planes at Stop 4: F-^ appears as crinkle 
folds in the more resistant dolostone beds 
with widely-spaced, quartz-filled cleavage 
planes. There is no evidence of F2 in this 
area. 



209 










lO 






210 




Fiaure 6 



211 



X- 






LEGEND 



Oc Cutting Dolomite 

Oct Cutting Dolomite - transitional 

Os Shelburne Formation 

€cs Clarendon Springs Dolomite 

€da Danby Formation 



Bedding 
Fi Cleavage 
Fz Cleavage 

Fi Hinge - C.W. Rotation 
Formation Contact 
r^/ Questionable Contact 
/ Hinesburg Thrust Fault 



212 



A.S.=N7E,29E 




500 1000 FEET 

SCALE 



Oc Cutting Dolomite 



Oct Cutting Dolomite -transitional 
Os Shelburne Formation 



PROFILE SECTION 



along the axial surface of Fi 



Figure 7 



213 




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214 



of Middle Cambrian age. It appears possible that an 
unconformity may have existed, at least locally, between 
the Winooski and Danby Formations during Middle Cambrian 
time. This basal conglomerate seems to indicate a period 
of uplift and erosion preceding the deposition of the 
massive quartzites of the lower Danby, Positive indenti- 
fication of the boulders has not been possible as yet 
but hold the key as to the existence of the Middle Cam- 
brian unconformity. 



REFERENCES 



Cady, W.M., 1945, Stratigraphy and structure of west- 
central Vermont t Geol. Soc. Amer. Bull., vol. 56, 
pp. 515-558. 

, i960, Stratigraphic and geotectonic relation- 
ships in northern Vermont and southern Quebec* Geol, 
Soc. Amer. Bull., vol. 71, pp. 531-576. 

Doll, C.G,, Cady, W.M., Thompson, J.B., Jr., and Billings, 
M.P., 1961, Centennial geological map of Vermont: 
Vermont Geol. Survey, Burlington, Vt., scale 1:250,000, 

Stanley, R.S,, I969, Bedrock geology of the southern 
portion of tho Ilinesburg synciinorivim (Vermont): 
rr. 40th Annual Meeting New York State Geol. Assoc, 
Plattsburgh, N.Y., May, 1969» Guidebook to field 
excursions, p. 36-64. 

Stone, C.W.and Dennis, J.G., 1964, The geology of the 
Milton quadrangle, Vermont: Vermont Geol. Survey 
Bull. 26, 79 p. 



Welby,C.W., 1961, 
of Vermont: 



Bedrock geology of the Champlain Valley 
Vermont Geol. Survey Bull, 14, 296 p. 



215 



Trip BIO 

LOWER PALEOZOIC ROCKS FLANKING THE 

GREEN MOUNTAIN ANTICLINORIUM 

by 

James B. Thompson, Jr. 
Department of Geological Sciences 
Harvard University 
Cambridge, Massachusetts 



Precambrian rocks designated the Mount Holly Complex (Doll 
et al. , 1961) crop out over a large area in the southern and 
central Green Mountains of Vermont. The rocks of the Mount 
Holly Complex are probably correlative with the Grenville Series 
of the southeastern Adirondacks as described by Walton and 
deWaard (1963) , and were metamorphosed and deeply eroded before 
the deposition of the Paleozoic (and perhaps also late Precam- 
brian) rocks that now overlie them with profound unconformity. 

All of the rocks have undergone severe Paleozoic deforma- 
tion and regional metamorphism. The younger rocks on the west 
limb of the Green Mountain anticlinorium are in the biotite zone 
and those to the east are mainly in the garnet zone. The fabric 
and mineralogy of the rocks of the Mount Holly Complex have been 
strongly affected by the Paleozoic deformation and recrystalliza- 
tion. These effects are generally most pronounced at or near the 
unconformity separating the Mount Holly from the younger units, 
where the original textures and mineral assemblages of the Mount 
Holly are locally almost obliterated by later recrystallization 
and development of a penetrative schistosity. The localization 
of these features is probably related in part to weathering on 
the Precambrian erosion surface and in part to fluids derived 
from the prograde metamorphism of the overlying sediments. 

The younger rocks on the west flank of the Green Mountain 
anticlinorium constitute the Champlain Valley Sequence as out- 
lined in Table 1. This sequence includes about 1500 feet of 
basal elastics of earliest Cambrian (and perhaps also late Pre- 
cambrian) age, overlain by about 3500 feet of Cambrian and Lower 
Ordovician carbonate rocks with minor intercalations of phyllite 
and quartzite. On the east flank of the anticlinorium, however, 
the Mount Holly is overlain by a much thicker sequence of schists 



216 



and phyllites containing several metavolcanic units. This se- 
quence, the Eastern Vermont Sequence as outlined in Table 2, 
also includes possible late-Precambrian, Cambrian and Ordovi- 
cian rocks. The allochthonous Taconic Sequence now located 
west of the Green Mountain region is outlined in Table 3. The 
Taconic Sequence is similar in many ways to the Eastern Vermont 
Sequence but contains more cr.rbonates and less evidence of vol- 
canic activity. It was presumably deposited in or near what is 
now the Green Mountain region, but the original site of deposi- 
tion is now foreshortened by subsequent deformation. The narrow 
septum of younger rocks extending north-northwest from Pico Peak 
(Figure 1) is of considerable interest in this regard. A ten- 
tative correlation between the rocks of the three main sequences 
of southern and central Vermont is given in Figure 2. 



The primary purpose of this field trip is 
interested geologists with the stratigraphic s 
limb of the Green Mountain anticlinorium in so 
mont. Most of the outcrops visited are on U.S 
Sherburne Center and Bridgewater Corners along 
Ottauquechee River. One stop (Stop 1) will be 
however, to see the upper part of the Cheshire 
basal units of the Rutland (Dunham) dolomite, 
this stop is to compare this sequence with a s 
one in the upper part (Plymouth Member) of the 
near Plymouth, Vermont (Stop 14) . 



to acquaint 
equence on the east 
uth-central Ver- 
. Highway 4 between 
the valley of the 
made near Rutland, 
quartzite and the 
The reason for 
trikingly similar 
Hoosac Formation 



The unconformity between the Tyson Formation and the under- 
lying Precambrian basement will be visited at Sherburne Center 
followed by representative exposures of the overlying Tyson, 
Hoosac, Pinney Hollow, Ottauquechee, Stowe and Missisquoi Forma- 
tions. The route of the excursion will pass through the type 
exposures of the Ottauquechee Phyllite and Pinney Hollow Schist 
as originally defined by E.L. Perry (1929) . 

The geologic sketch map (Fig. 1) is modified from the Cen- 
tennial Geologic Map of Vermont (Doll et al. , 1961) on the basis 
of recent geologic investigations by the author and by P.H. 
Osberg (1959, and later communications). All outcrops to be 
visited are in the Rutland and Woodstock quadrangles (U.S.G.S. 
15' series) for which there are published maps by W.F. Brace 

(1953) and by Chang, Ern, and Thompson (1965), respectively. 
Other publications pertinent to the area of the excursion are 
those of Thompson (1959, 1967), Zen (1961, 1964) and Osberg 

(1959) for the area near Rutland on the west flank of the Green 
Mountains, and those of Osberg (1952) and Ern (1963) for the cen- 
tral Green Mountain area and the region immediately to the east. 



217 



The route of the excursion is also covered by new topo- 
graphic maps of the U.S.G.S. 7 1/2' series. The route of the 
excursion passes through parts of the Rutland, Chittenden, Pico 
Peak, Killington Peak and Plymouth quadrangles in that order. 

The arguments for the dating of the Eastern Vermont Sequence 
have been summarized by Chang et al . (1965) . The dating of the 
Champlain Valley Sequence has B¥en reviewed by Theokritoff and 
Thompson (1969) who also summarize recent findings on the dating 
of the Taconic Sequence. The correlations implied by Figure 2 
are at least consistent with the paleontologic data now avail- 
able. One of the principal differences between Figure 2 and 
the correlations of other authors (Zen, 1967, Plate 2, for ex- 
ample) is in the dating of the Tyson, Hoosac and Pinney Hollow 
Formations relative to the lower part of the Champlain Valley 
Sequence. The evidence for the revisions proposed here is 
admittedly circumstantial and is based in part on the intriguing 
similarity between the sequences to be seen at Stop 1 and at 
Stop 14 on this excursion. A second major factor influencing 
the construction of Figure 2 is the presence of iron ores at 
the contact between the dolomite member of the Tyson Formation 
and the overlying albite schists of the Hoosac Formation as 
seen at Stop 7. This is taken as evidence for a period of sub- 
aerial erosion and correlated with similar occurrences reported 
by Booth (1950) and others at the contact between the White 
Brook Dolomite and West Sutton Formation in northwestern Vermont 
and southern Quebec. 



218 



Table 1 

Cambrian and Lower Ordovician rocks of the Champlain Valley 
Sequence near Rutland, Vermont (Modified from Thompson, 19 67) 



Bascom Formation (Ob) Lower Ordovician 

Interbedded calcite marble and dolostone. (350-400') 

Shelburne Marble (Os) Lower Ordovician 

White calcite marble. (250') 



Clarendon Springs Formation (-Gcs) Upper Cambrian 

Upper member: Cherty dolomite. (150-200') 

Sutherland Falls member: White calcite marble, dolomitic 

curdling. (50-100') 
Lower member: Gray calcitic dolomite, cross-bedded sandy 

dolomite. (200-250') 



Danby Formation (€d) Upper Cambrian 

Interbedded vitreous quartzite and cross-bedded sandy 
dolomite. (50-150') 



Winooski Dolomite (€w) Middle Cambrian 

Varicolored dolomites, minor dolomitic quartzite and 
schistose quartzite. (300-400') 

Monkton Quartzite (-Gm) Lower Cambrian 

Quartzite, schistose quartzite and feldspathic quartzite 
interbedded with varicolored dolomites and minor 
phyllite. (300') 

Rutland (Dunham) Dolomite (-Gr) Lower Cambrian 

Gray and yellow weathering dolomites, thin siliceous 
partings. (900') 



219 



Table 1 Continued 

Cheshire Quartzite (-Gc) Lower Cambrian 

Mainly vitreous quartzite, gray to black quartzose 
phyllite in lower part. (1000-1600') 

Dalton Formation (€dt) Probably Lower Cambrian 

Schistose graywacke, conglomerate, minor phyllite; 
discontinuous dolomite or sandy dolomite near top. 
(50-300') 

Table 2 

Cambrian and Ordovician rocks of the Taconic Sequence near 
Rutland, Vermont (Modified) from Zen, 1961; Thompson, 1967; 
Theokritoff and Thompson, 1969) 

Pawlet Formation Middle Ordovician 

Graywacke and interbedded black slate. (700') 

Indian River Slate Middle Ordovician 

Red and blue-green slate. (200') 

Poultney Slate Lower Ordovician 

Mainly thin-laminar, siliceous slates, minor limestones 
near base. (600 ') 



Hatch Hill and West Castleton Formations Lower to Upper 

Cambrian 
Black slate, dolomitic quartzite, minor limestone. (500') 



Bull Formation Lower Cambrian 

Mettawee Slate: Purple and green slate, thin limestone 
conglomerate near top; green phyllites or schists 
(St. Catharine Formation) in eastern Taconics. 

Bomoseen Graywacke: Graywacke, minor slate and quartzite; 
albitic phyllites with quartzite, dolomite and limestone 
in upper part (Netop Formation of Thompson, 196 7) in 
eastern Taconics. (600') 



220 



Table 3 

Cambrian and Ordovician rocks of the Eastern Vermont Sequence 
(Modified from Chang et al., 1965) 



Missisquoi Formation (Om) Lower and Middle Ordovician 

Cram Hill Member: Black, sulfidic schist, schistose 
quartzite. (250') 

Barnard Volcanic Member: Biotite gneiss, hornblende 
gneiss, amphibolite (2500') 

Moretown Member: Quartzite and quartz feldspar granulite 
with thin micaceous partings producing a "pinstripe" 
texture. (2000') 

Whetstone Hill Member: Gray to black phyllite, micaceous 
quartzite, amphibolites , coticule and quartz-garnet- 
magnetite rock. Minor pinstripe quartzite. (2000') 



Stowe Formation (OKTs) Ordovician or Cambrian 

Quartz-sericite-chlorite schist with garnets and biotite 
abundant locally. (1500') 



Ottauquechee Formation (€o) Lower to Upper Cambrian 

Black, sulfidic phyllite or schist, quartz-sericite- 
chlorite-schist with garnet and biotite. Vitreous 
quartzites, some of which are carbonaceous, occur as 
beds to ten feet thick near base, but thinner and less 
abundant above. Greenstones and actinolitic green- 
stones occur locally. (3000') 

Pinney Hollow Formation (-Cph) Lower Cambrian 

Quartz-sericite-chlorite schist-biotite and garnet 

abundant locally and green chloritoid phyllite abundant 
in lower part. Some layers of chloritoid phyllite have 
a faint purplish color due to hematite. Greenstone and 
actinolitic greenstone in upper part. (2000') 



221 



Table 3 Continued 



Hoosac Formation (€h) Lower Cambrian 

Albitic schists, schistose feldspathic quartzites, 

carbonaceous schists near top. Middle and upper part 
of formation (Plymouth Member) contains vitreous 
quartzite, dolomite, dolomite breccia and dolomite 
with carbonaceous partings. (1250') 



Tyson Formation (-Gt) Probably Lower Cambrian 

Upper member: Dolomite characterized by lenses of mag- 
netite or hematite at or near top. These were formerly 
mined as iron ore and may be a metamorphosed terra 
rosa . (200') 

Middle member: Quartzite and pebbly quartzite inter- 
bedded with calcitic and dolomitic marbles and black 
phyllite. (250') 

Lower member: Conglomerate and schistose graywacke . 
(350') 



222 



73°00 




- 43°45' 



73°00' 



72''45' 



43''30' 



Figure 1 . Geologic sketch map of a part of south-central 
Vermont, modified from Doll et al. (1961) . 
Symbols as in Tables 1 and 3. Dotted line is 
route of excursion starting at Rutland (R) with 
stops numbered as in road log. Scale 1:250,000, 



223 





Champlain Valley 


Taconic Range 


Eastern Vermont 


Middle 
Ordovician 


Ira Fm. 


Pawlet Fm. 


Missisquoi 
Fm 


Indian River 
Slate 


Baker Brook 
Volcanics 


Lower 
Ordovician 


Bascom Fm. 


Poultney Slate 


Shelburne Marble 


Stowe Fm. 


Upper 
Cambrian 


Clarendon 
Springs Fm. 


Hatch Hill Fm. 


Ottauquechee 
Fm. 


Danby Fm. 


Middle 
Cambrian 


Winooski Dol. 


West Castleton 
Fm. 


Monkton Qte . 


Lower 
Cambrian 

- 


Rutland Dol. 


Mettawee Slate 


Pinney Hollow Fm 


1 

1 
Bomoseen| Netop 

Gray- , Fm. 

wacke |^ 


Hoosac Fm. 


Cheshire Qte. 


Dal ton Fm. 


Conglomerates on 
Bird Mtn.? 


Tyson Fm. 



Figure 2 . Stratigraphic correlation of some Cambrian and Ordo- 
vician rocks in south-central Vermont. 



224 



Road Log for Trip BIO 

Starting point is the municipal parking lot opposite the 
Hotel Bardwell (near City Hall) , Rutland, Vermont (Rutland 
7 1/2 minute quadrangle) . 

Mileage 

0.0 Parking lot, proceed north via Merchants Row and Grove 
Street. 

1.4 Enter Chittenden 7 1/2 minute quadrangle and pass 
golf course on left with exposures of Rutland (Dunham) 
Dolomite. 

1.7 Cross East Creek (Lower Cambrian fossils upstream, 
Theokritoff and Thompson, 1969, Stop 2). 

2.2 Stop 1 : Power line crossing. Walk west over expos- 
ures of dolomite breccia at base of Rutland Dolomite. 
Topmost beds of Cheshire Quartzite are exposed on 
hill 0.15 miles W. 

2.6 Turn E. (right) on McKinley Lane and follow to U.S. 
Highway 7 . 

3.7 Turn N. on U.S. 7. 

3.9 Turn E. on Post Road. 

4.9 Rutland Dolomite on left. 

5.6 Turn right (E.) on Park Lane and follow to U.S. High- 
way 4 . 

6.5 Turn left (N.) on U.S. 4. Outcrops just N. on right 
are part of Mount Holly Complex. 

6.9 Mendon Village. A fairly complete section from the 
Mount Holly Complex, through the Dalton Formation, 
into the lower part of the Cheshire Quartzite is 
exposed about one mile north of here at the W. base 
of Blue Ridge Mountain. This is the type locality 
for the Mendon Series of C.L. Whittle (1894, p. 408- 
414). Proceed E. on U.S. 4 past outcrops (7.3-8.0) 
on right of gneisses, schists, quartzites and calc- 
silicate marbles of Mount Holly Complex. 

9.8 Enter Pico Peak 7 1/2 minute quadrangle. 



225 



11.2 Beaver Pond on left. In notch one mile northwest 
(accessible via Elbow Rd . ) are extensive exposures 

of dolomites now assigned to the Tyson Formation, 
and also, on the hill E. of the notch, of the lower 
part of the Hoosac Formation. 

11.7 Pico Ski Area on right. 

12.3 Stop 2 ; Summit of Sherburne Pass. Outcrop S. of 
road and ledges on Deer Leap Mountain to N. are 
gneissic conglomerate and metagraywacke now assigned 
to the Tyson Formation. These rocks are in the Pico 
syncline, a narrow, east-dipping septum containing 
rocks of the Eastern Vermont Sequence. The eastern 
boundary of the septum is probably a major thrust 
fault. Outcrops E. of pass are in Mount Holly Complex, 

13.8 Junction with Route 100, proceed E. on U.S. 4 past 
access road to Killington Ski Area. Outcrops of 
gneisses of Mount Holly Complex appear sporadically 
on right side of road over next mile and a half. 

15.5 Start of long road cut on right in Mount Holly Complex, 

15.7 Stop 3 : Unconformity at base of Tyson Formation is 
exposed, though perhaps not convincingly, near east 
end of cut about 0.1 mi N.W. of Sherburne Center. 
The phyllonites derived from schists and gneisses of 
the Mount Holly are not easily distinguished here 
from the schistose metagraywackes of the Tyson Forma- 
tion, — a bad place for a beginner! 

15.9 Stop 4 ; Just S. of Sherburne Center. Deformed poly- 
mictic conglomerates in lower part of Tyson Formation. 
Admire, but please do not destroy, the pebbles of 
blue opalescent quartz near the south end of the 
outcrop. 

16.8 Stop 5 : Unconformity at base of Tyson Formation is 
exposed on right near northeast base of outcrop. 
Note graded beds and onlap relations in basal part 
of Tyson. This outcrop should be preserved with 
care; hammering will not improve it in any way! 

18.0 Stop 6 ; Carbonaceous, pyritic phyllites, dolomites 
and dolomitic quartzites in central part of Tyson 
Formation. These rocks underlie the upper, dolomite 
member of the Tyson which here controls the course 
of the headwaters of the Ottauquechee River. The 
conspicuous quartz vein is probably related to 
boudinage . 



226 



i 



18.3 Enter Killington Peak 7 1/2 minute quadrangle. 

18.4 Turn left on small side road and cross river. 

18.6 Stop 7 : Overhanging ledges E. of road are albitic 
schists at the base of the Hoosac Formation. The 
basal beds of the Hoosac contain abundant magnetite. 
Dolomite at top of Tyson Formation is exposed beneath 
overhang and contains lenticular masses of iron oxides 
that were once mined farther south in Plymouth as 
iron ore. These are thought to be a metamorphosed 
terra rosa and to indicate a period of subaerial 
erosion between the deposition of the Tyson and Hoosac 
Formations. The iron ores are probably correlative 
with those in northwestern Vermont and southern Quebec 
at the contact between the White Brook Dolomite and 
the overlying West Sutton Formation (Booth, 19 50, 
p. 1146-7) . 

18.9 Outcrops of dolomite on left below overhanging ledges 
of albite schist. 

19.2 Rejoin U.S. 4 and turn left, outcrops on right are 
quartzites in Hoosac Formation. 

20.2 West Bridgewater, enter Plymouth 7 1/2 minute auad- 

rangle. Outcrops in gravel pit to N.E. are carbonaceous 
phyllites in upper part of Hoosac Formation. 

20.6 Stop 8 ; Green chloritoid phyllites of Pinney Hollrw 

Formation, some are faintly purplish owing to hematite. 
Assemblage is quartz-muscovite-paragonite-chlorite- 
chloritoidihematite . To east along base of bank are 
phyllites with the assemblage quartz-muscovi te- 
chier ite-albite-garnet-biotite-magnetite-py rite. 

21.6 Stop 9 : Carbonaceous, sulfidic phyllite and inter- 
bedded carbonaceous quartzites in lower part of 
Ottauquechee Formation. Some beds contain biotite 
and small garnets. 

22.4 Carbonaceous schist and greenstone in Ottauquechee 
Formation. 

22.8 Stop 10 ; Quartz-sericite-biotite-garnet schists of 
Ottauquechee Formation. Outcrop shows interbedding 
of carbonaceous and non-carbonaceous varieties. 

24.2 Stop 11 ; Typical schist of Stowe Formation. Note 
abundant quartz lenses. These probably represent 
silica produced by metamorphic reactions. Outcrop 
is in garnet zone. 



227 



24.6 Enter Missisquoi Formation. 

25.2 Stop 12 ; Carbonaceous schist and gray quartzites of 
Whetstone Hill Member of Missisquoi Formation. 

25.8 Bridgewater Corners, turn right (S.) on Route lOOA. 

26.4 Stop 13 ; "Pinstripe" in Missisquoi Formation. This 
is the characteristic rock type of the Moretown 
Member although these particular outcrops are in the 
Whetstone Hill Member. Quartz-garnet-magnetite 
layers are probably recrystallized Fe-Mn cherts. 
Note rosettes of grunerite, but please spare for 
subsequent field trips. 

27.1 Road bears right. Next four miles up Pinney Hollow 
repeats the Ottauquechee River section in reverse 
order. 

27.2 Re-enter Stowe Formation. 

27.9 Enter Ottauquechee Formation. 

28.9 Carbonaceous schists and quartzites, Ottauquechee 
Formation. 

29.2 Enter Pinney Hollow Formation. 

30.6 Green chloritoid phyllites of lower Pinney Hollow 
Formation. Some purplish bands with hematite. 

30.9 Enter Hoosac Formation. 

31.0 Dolomites on left in upper part of Hoosac Formation. 

31.4 Bear right to Plymouth Village. 

31.6 Center of town, proceed straight ahead by cheese 
factory. 

32.1 Bear left at fork in road (old limekilns on left). 

32.3 Stop 14 ; Dolomite breccia (west of road) in Plymouth 
Member of Hoosac Formation. This rock closely 
resembles the dolomite breccia in the basal beds of 
the Rutland Dolomite at Stop 1. Outcrops in woods 
west of pasture are of underlying quartzites resem- 
bling the Cheshire Quartzite at Stop 1. The same 
quartzites may be seen 0.7 miles S. on Route lOOA at 
Plymouth Notch. Descent from Plymouth Notch to 
Plymouth Union gives a fairly complete section through 
albitic schists of lower part of Hoosac Formation. 
Contact with dolomite of Tyson Formation is exposed 
just N.E. of junction with Route 100. 



228 



References, Trip B-10 



Booth, V.H., 1950, Stratigraphy and structure of the Oak Hill 
succession in Vermont: Geol. Soc. America Bull., v. 61, 
pp. 1131-1168. 

Brace, W.F., 1953, The Geology of the Rutland area, Vermont: 
Vermont Geol. Survey Bull. 6, 120 p. 

Chang, P.H., Ern, E.H., Jr. and Thompson, J.B. Jr., 1965, Bed- 
rock geology of the Woodstock quadrangle, Vermont: Vermont 
Geol. Survey Bull. 29, 65 p. 

Doll, C.H., Cady, W.M. , Thompson, J.B., Jr., and Billings, M.P., 
1961, Centennial Geologic Map of Vermont: Vermont Geol. 
Survey. 

Ern, E.H., Jr., 1963, Bedrock geology of the Randolph quadrangle, 
Vermont: Vermont Geol. Survey Bull. 21, 96 p. 

Osberg, P.H., 1952, The Green Mountain anticlinorium in the 

vicinity of Rochester and East Middlebury, Vermont: Vermont 
Geol. Survey Bull. 5, 127 p. 

, 1959, Stratigraphy and structure of the Coxe Mou'-- 

tain area, Vermont, Trip F: New England Intercoll. Ceol. 
Conf., Buidebook, 51st Ann. Mtg., Rutland, Vermont, 
p. 45-53. 

Perry, E.L., 1929, The geology of Bridgewater and Plymouth 

Townships, Vermont: Vermont State Geologist 16th Rept. , 
1927-1928, p. 1-64. 

Theokritoff, George and Thompson, J.B., Jr., 1969, Stratigraphy 

of the Chcunplain Valley Sequence in Rutland County, Vermont, 
and the Taconic Sequence in northern Washington County, 
New York, Trip 7: New England Intercoll. Geol. Conf., 
Guidebook, 61st Ann. Mtg. Albany, New York, p. 7/1-7/26. 

Thompson, J.B., Jr., 19 59, Stratigraphy and structure in the 

Vermont Valley and the eastern Taconics between Clarendon 
and Dorset, Trip H: New England Intercoll. Geol. Conf., 
Guidebook, 51st Ann. Mtg., Rutland, Vermont, p. 71-87. 



229 



, 1967, Bedrock geology of the Pawlet quadrangle 



Vermont, Part II, Eastern portion: Vermont Geol . Survey 
Bull. 30, p. 61-98. 

Walton, M.S. and deWaard, Dirk, 1963, Orogenic evolution of the 
Precambrian in the Adirondack Highlands, a new synthesis: 
Proc. Kon. Ned. Akad. Wetensch., Amsterdcim, B, 66, p. 98-106 

Whittle, C.L., 1894, The occurrence of Algonkian rocks in Ver- 
mont and the evidence for their subdivision: Jour. Geol., 
V. 2, p. 396-429. 

Zen, E-an, 1961, Stratigraphy and structure at the north end 
of the Taconic Range in west-central Vermont: Geol. Soc . 
America Bull., v. 72, p. 293-338. 

, 1964, Stratigraphy and structure of a portion of 

the Castleton quadrangle, Vermont: Vermont Geol. Survey 
Bull. 25, 70 p. 

, 1967, Time and space relationships of the Taconic 

allochthon and antochthon: Geol. Soc. America, Special 
Paper 97, 107 p. 



231 



Trip B-11 



GEOLOGY OF THE GUILFORD DOME AREA, 
SOUTHEASTERN VERMONT 



by 



J. Christopher Hepburn, Department of Geology and Geophysics, 
Boston College, Chestnut Hill, Massachusetts 02167, 



Introduction 



The Guilford dome lies within the broad outlines of the 
regional Connecticut Valley-Gaspe' synclinorium. This syn- 
clinorium, principally underlain by Siluro-Devonian rocks, 
separates the Oliverian gneiss-cored domes of the Bronson Hill 
anticlinorium to the east from the Green Mountain anticlinorium 
to the west. The Guilford dome is part of a belt of domes that 
extends southward from east-central Vermont to Connecticut, 
west of the Connecticut River, analogous to but more widely 
spaced than the domes of the Bronson Hill anticlinorium. Large 
recumbent folds are found in the strata mantling these domes in 
eastern Vermont (Doll et. al. , 1961; Rosenfeld, 1968). The 
Standing Pond Volcanics is an important marker unit outlining 
many of these recumbent folds and domes. The axial surfaces of 
the recumbent folds have been arched by the later doming. The 
arcuate, closed, double band of the Standing Pond Volcanics 
around the southern end of the Guilford dome (Fig. 1) outlines 
such a refolded recumbent fold. One of the main purposes of 
the field trip is to investigate this fold and the proposed 
east-facing recumbent anticline above it. Other stops will be 
made to view the Black Mountain Granite, an important key in 
determining the time of deformation; the Siluro-Devonian Waits 
River Formation in the exposed core of the dome; and the Putney 
Volcanics, which separates the "Vermont" and "New Hampshire" 
seauences . 



Acknowledgements 



Geological mapping of the Guilford dome area was part of 
a Ph.D. thesis at Harvard University under the direction of 
Professors M. P. Billings and James B. Thompson, Jr., whose 



232 



help the author would particularly like to acknowledge. I 
would also like to thank the many persons who assisted during 
the course of the field work. Financial assistance of the 
Reginald and Louise Daly Fund, Harvard University, is 
gratefully acknowledged. 

Stratigraphy 



Please refer to Skehan and Hepburn (this volume) , Strat- 
igraphy of the East Limb of the Green Mountain Anticlinorium , 
Southern Vermont , for a brief description of most of the 
stratigraphic units and for a regional correlation chart. The 
units most pertinent to this trip are summarized below. 

Middle Ordovician 

BARNARD VOLCANIC MEMBER, MISSISQUOI FORMATION: 4000-8000 feet 
thick. Massive porphyritic and non-porphyritic amphibolites , 
feldspar-rich gneisses, and layered gneisses. 

Siluro-Devonian 

SHAW MOUNTAIN FORMATION: 0-20 feet thick. Quartzite and 
quartz-pebble conglomerate, hornblende fasciculite schist, 
amphibolite, and mica schist. 

NORTHFIELD FORMATION: 1000-2500 feet thick. Gray mica schist 
with abundant almandine porphyroblasts , minor impure quartzite 
and impure punky-brown weathering marble. 

WAITS RIVER FORMATION: 3000-7500 feet thick. Mica schist 
(phyllite at lower metamorphic grades) and calcareous mica 
schist with abundant interbeds of punky-brown weathering, 
impure marble; thin interbeds of micaceous quartzite. Quartz- 
itic member : feldspathic and micaceous quartzite interlayered 
with muscovite schist. 

STANDING POND VOLCANICS : 0-500 feet thick. Medium-grained 
amphibolite and epidote amphibolite; garnet-hornblende 
fasciculite schist. Eastern band : plagioclase-biotite- 
hornblende-quartz granulite and gneiss. 

GILE MOUNTAIN FORMATION: 2500-5000 feet thick. Light gray 
to gray, micaceous and feldspathic quartzite and mica schist; 
gray fine-grained phyllite and slate with interbedded, thin 
micaceous quartzite; and rare impure marble. Marble member : 
black phyllite with interbeds of punky-brown weathering , Impure 
marble and micaceous quartzite. 



233 



PUTNEY VOLCANICS: 0-400 feet thick. Light, greenish gray 
phyllite; buff to light brown \:eathering feldspathic phyllite; 
thin beds of feldspathic granulite; and minor gray slate. 
Conglomeratic member : lenses of polymict conglomerate with a 
gray slate matrix; pebbles abundant to scarce. 

LITTLETON FORMATION: 5000-6000 feet thick. Gray slate or 
phyllite with interbedded quartzite. 

Early to Middle Devonian Intrusive Rocks . 

BLACK MOUNTAIN GRANITE: Medium-grained two-mica granodiorite , 
correlated with the New Hampshire Plutonic Series (Billings, 
1956) . 



No new definitive evidence for the facing of the Waits 
River, Standing Pond, and Gile Mountain Formations has yet been 
found by the author. However the sequence, oldest to youngest, 
of Waits River, Standing Pond, and Gile Mountain, as shown on 
Figure 1 is favored, although a possible inversion of this 
order cannot be ruled out. 



The Putney Volcanics (Stops 1 and 2) consists of a belt 
of rocks that were formerly included in the Standing Pond Volc- 
anics (Doll et al. , 1961; Trask, 1964). Since the proper 
correlation of these rocks has not yet been established, 
Hepburn (1972) designated them as a separate formation. 

Structural Geology 

The major tectonic features in the Guilford dome area 
formed during the Acadian orogeny, between the end of sediment- 
ation in the Early Devonian and the crystallization of late, 
unoriented, coarse muscovite crystals in the Black Mountain 
Granite 377-383 m.y. ago (Naylor, 1971). Late normal faulting 
and possibly some minor folding occurred during the Triassic. 
The two major stages of deformation in the area include (1) the 
development of large recumbent folds, followed by (2) the rise 
of the Guilford dome. 



The doubly-closed loop of the Standing Pond Volcanics 
around the southern part of the Guilford dome outlines the 
Prospect Hill recumbent fold, named for exposures at the hinge 
(Stop 3) . The Gile Mountain Formation forms the core of the 
fold. Originally the Prospect Hill fold had a subhorizontal 



23^ 



axial surface and a hinge striking northeast-southwest. The 
subsequent doming about a roughly N-S axis arched the axial 
surface of the recumbent fold, so that now the hinge plunges 
moderately northeast and southwest away from the axial trace of 
the Guilford dome. An early, tight, now overturned, steeply 
east-dipping synform must lie between the Standing Pond bands 
in the doubly-closed loop and a third band lying to the east of 
the Guilford dome (Fig. 1) . The hinge line where the Standing 
Pond rocks cross the axial surface of this synform is not seen 
in the Brattleboro area and is presumably buried. This synform, 
the Northfield Formation around the north end of the Guilford 
dome, and the Fall Brook anticline which exposes the Barnard 
Volcanics, are interpreted as the upper (anticlinal) portion 
of the Prospect Hill fold (Fig. 1, Cross-section A). 

It is very likely that the Prospect Hill fold is con- 
tinuous with the Ascutney sigmoid in the Saxtons River quad- 
rangle to the north (Rosenfeld, 1968; Doll et al . , 1961). If 
this is true, the hinge of the Prospect Hill fold must turn 
more northerly a short distance north of Stop 3 . 

The Guilford dome, which occupies much of the central* 
portion of the Brattleboro quadrangle (Fig. 1), is a large, 
elliptical, doubly-plunging anticline formed during the second 
major stage of deformation. The Waits River Formation forms 
the exposed core of the dome. The foliation dips away in all 
directions from the axial trace, which strikes slightly east of 
north and plunges moderately to the north and south at the ends 
of the anticline. The axial surface of the dome dips very 
steeply to the west. A small depression in the exposed central 
portion of the dome divides it into a northern and southern 
lobe. The axial trace of the dome is closer to its eastern 
side. Here, the foliation has steep dips a short distance east 
of the axial trace. Dips are more gentle to the west. Bedding 
with a schistosity parallel to it has been arched by the dome. 

It is likely that the two major stages of deformation 
were not greatly separated in time. 

Minor Folds 



Minor folds of at least five different stages are present 
in the Guilford dome area and the Brattleboro syncline to the 
east of the dome. These stages of minor folding are summarized 
below: 



235 



Fl. Small isoclinal folds in layering, with schistosity 
developed parallel to the axial surfaces (Stop 3) . 

F2. Tight to isoclinal folds congruous with the large-scale 
recumbent folding (Prospect Hill fold) . These fold the 
schistosity and the Fl folds. Weak to moderate axial- 
planar cleavage. Plunge moderately NE . or SW. 

F3. Open folds, particularly west and south of the Guilford 
dome. Excellent slip-cleavage developed parallel to the 
axial surfaces. The axial surfaces generally strike NE. 
and dip steeply NW. The hinges plunge moderately NE. 
Excellent crinkle lineations occur at the intersection of 
this slip-cleavage and the schistosity surfaces in the 
pelitic rocks. 

F4. Open folds, buckles or warps in the foliation that are of 
one or more generations and fold the slip-cleavage. 

F5. Large open folds found only in the eastern part of the area 
(Fig. 1) that offset the Putney Volcanics with an east- 
side-north movement. Plunge is moderately to steeply 
north. Kink bands also found along the eastern part of 
Figure 1 are the youngest minor folds and may be related 
to the above F5 folds or may be younger. 

Met amor phi sm 

A belt of low-grade metamorphic rocks (chlorite zone) 
occurs in the eastern part of the area and roughly follows the 
Connecticut River. This low is of regional extent (Thompson 
and Norton, 1968) and separates terrains of higher metamorphic 
grade along the Bronson Hill anticlinorium from those in the 
domes of eastern Vermont. The highest grade of regional meta- 
morphism in the Guilford dome area, staurolite-kyanite zone, 
is centered on the dome. The peak of metamorphism probably 
closely followed the doming stage of major deformation. During 
the earlier recumbent folding, the grade of metamorphism did 
not exceed the garnet zone. 



236 



FIGURE 1 




72'30' 



GEOLOGIC MAP OF THE BRATTLEBORO AREA 



237 



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Geology of the Guilford dome area, 
southeastern Vermont. 



Road Log for Field Trip, Sunday Oct. 15 
J. Christopher Hepburn, Leader 

Assemble at STOP 1 at 10;30 a.m. This will allow plenty 
of time for participants leaving Burlington by 8:00 a.m. to 
arrive. The trip will never be more than a few miles from 191 
for those who must leave early. Bring lunches. 

Topographic map : Scheduled stops will be in the Brattleboro 
15 minute quadrangle , Vermont-New Hampshire. The Geologic Map 
of Vermont by Doll et al^. (1961) may also be of interest and is 
available from the Vermont State Library, Montpelier for $4.00. 

Mileage 

From Burlington take 189 south to 191. Then 191 south 
to Exit #3, the first Brattleboro exit from the north, 
marked "To Route 9 east, Keene , N.H.; and Route 5, 
Brattleboro" . 

0.0 At the junction of Routes 5, 9, and 91 north of Brattle- 
boro by Howard Johnson' s Restaurant just off Interstate 
Exit #3, turn left (north) onto Route 5. 

0.7 Overpass over 191. 

0.9 Brattleboro-Dummerston town line. 

1.2 STOP 1 . Meeting Place , PUTNEY VOLCANIC S . Park in rest 
and picnic area on the east side of Route 5. 

The Putney Volcanics (Hepburn, 1972) in this area 
consists of fine-grained, poorly foliated, light 
greenish gray quartz-plagioclase-muscovite phyllites and 
granulites with interbedded gray slates. The granulites 
and feldspathic phyllites weather buff to light brownish 
gray, characteristic of feldspar-rich rocks. Many of 
the foliation surfaces have a notable silky sheen. 
Small, brownish pits where carbonate has weathered out 
are common. The granulite beds may show a fine lamin- 
ation. A few lenses of quartz-pebble conglomerate may 
be seen along Route 5 south of the highway pull-off but 
are much better developed at Stop 2. The rocks have been 
metamorphosed to the chlorite zone at this locality. 
Continue north on Route 5. 

1.4 Outcrop of Putney Volcanics to the east. 

1.5 Outcrop of Putney Volcanics to the west. 

2.1 Slate quarry in Littleton Formation to the east. 



239 



2.3 STOP 2 . PUTNEY VOLCANICS , CONGLOMERATIC MEMBER . Park 
at left (west) side of road in the highway pull-off. 

Examine outcrops of gray slate in the Littleton 
Formation on the east side of Route 5. Then walk 0.1 
mile north through woods to an abandoned chicken-yard 
beside houses to west of Route 5. Outcrops are of the 
conglomeratic member of the Putney Volcanics . The 
contact of this conglomerate with the Littleton Form- 
ation represents the division between the "Vermont" and 
"New Hampshire" sequences in this area. The conglomer- 
ate contains both quartzite and slate pebbles in a 
slate matrix. (As this is the best exposure and type 
locality for the conglomerate, NO HAMMERING — PLEASE!). 
The excess of matrix over clasts in the conglomerate 
indicates it best fits Pettijohn's (1957) classification 
as a paraconglomerate. Pettijohn (1957, pp. 265-266) 
states that "it now seems probable in light of our 
knowledge of turbidity currents and related mudstones 
that most of these abnormal conglomerates [the para- 
conglomerates] are the product of subaqueous mudslides 
or slurries". 

A few small porphyroblasts of light pink garnet 
occur here. The outcrop is included in the chlorite 
zone, however, as probe analyses indicate these garnets 
contain up to 15.9 weight percent MnO. (The garnet 
isograd has been mapped on the first appearance of 
almandine in the pelitic rocks.) 

Immediately west of the conglomerate in this out- 
crop, the Putney Volcanics consists of slate with f eld- 
spathic granulite interbeds up to 2 feet thick. The 
granulites have fine laminations. M. P. Billings (1971, 
personal communication) indicated that a number of years 
ago he had found cross-bedding in these granulites that 
indicated tops to the west. This stop has become more 
overgrown in recent years, since the chickens left. 

West of the abandoned chicken-yard a sequence of 
phyllites and feldspathic granulites similar to those at 
Stop 1 is exposed on the side of the hill. 

Return to cars . Continue north on Route 5 . 

2.4 Road junction with dirt road on right. Continue north 
on Route 5 . 

2.6 Roger's Construction Co. yard on right (east), possible 
alternate parking for Stop 2 . 

2.9 Dutton Pines State Forest. 

3.4 Road junction with road to East Dummerston; continue on 

Route 5. Outcrop of Putney Volcanics to west. 
3.8 Road junction. Turn left (west) on road to East 

Dummerston and Dummerston Center. 

4.7 Road junction in East Dummerston; continue straight. 

4.8 Junction with road on right; continue straight. 



240 



4.9 Outcrop of Waits River Formation. 

5.9 Dummerston Center. Turn sharp left (south). 

6.0 STOP 3 . NORTHFIELD FORMATION . Park along side of road. 

Walk west to outcrops of the Northfield Formation 
exposed near the hinge area of the recumbent anticline 
above the Prospect Hill fold (See Fig. 1) . The North- 
field here is a gray well-foliated mica schist with 
conspicuous garnet porphyroblasts and fewer porphyro- 
blasts of biotite and staurolite. A few thin inter- 
bedded quartzites are also present. 

Turn around; return north to Dummerston Center. 

6.1 Dummerston Center. Turn left (west) on paved road past 
the fire station. 

6.5 STOP 4 . HINGE OF PROSPECT HILL FOLD, WAITS RIVER 

FORMATION AND STANDING POND VOLCANICS . Park in road 
pull-off on north side of the road just before the 
curve . 

The Standing Pond Volcanics outline the north- 
easterly plunging hinge of the Prospect Hill recumbent 
fold at this locality (Fig. 1) . A 1/2 mile traverse 
will be made around the hinge, following the contact 
between the amphibolites of the Standing Pond Volcanics 
and the schists, calcareous schists, and impure marbles 
of the Waits River Formation. This traverse presents an 
excellent opportunity to view a well-exposed hinge of a 
major recumbent fold. The contact is sharp and is easy 
to follow. The traverse starts just east of the pull- 
off near a very small creek along the eastern contact of 
the Standing Pond Volcanics. Follow this contact to the 
north and around the northeasterly plunging hinge of the 
recumbent fold, which closes on the lower south-facing 
slopes of Prospect Hill. Continue along the contact 
southward (now the western contact of the Standing Pond 
with the Waits River) . The paved road is encountered 
again 1/4 mile west of the starting point. 

If time permits. Prospect Hill will be climbed for 
the excellent view from the open summit (perhaps lunch) . 
Please be particularly careful on this traverse with 
litter and the indiscriminate use of hammers. We are 
able to make this stop only with special permission. 

Particular note should be made of the minor folds 
during the traverse. The most common folds are the F2 
generation, those formed congruously with the recumbent 
folding. These plunge NE. and show a reversal in drag 
sense around the hinge. A few Fl minor folds that pre- 
date the recumbent folding, have the principal schist- 
osity parallel to their axial surfaces, and are refolded 
by the F2 folds are visible in outcrops near the road. 
Return to cars; proceed west on paved road. 

6.7 Outcrops of the Standing Pond Volcanics in the hinge of 
the Prospect Hill recumbent fold. 



241 



6.8 Contact of the Standing Pond Volcanics with the Waits 
River Formation. 

6.9 Junction with dirt road to south; continue straight on 
paved road. 

7.4 Outcrop of aplitic dike associated with the Black 
Mountain Granite. 

7.8 Junction with road from right (north); continue straight. 

8.5 Road junction; take sharp left onto dirt road. 

9.3 STOP 5 . BLACK MOUNTAIN GRANITE . Park by abandoned 

quarry buildings and follow path east to the abandoned 
Presbury-Leland granite quarry. 

The Black Mountain Granite is a late synorogenic to 
post-orogenic two-mica granodiorite correlated with the 
New Hampshire Plutonic Series (Billings, 1956). Note 
the weak foliation produced by the alignment of the 
fine-grained micas. Coarse, unoriented muscovites that 
are younger than this foliation have been dated by 
Naylor (1971) from this locality. He obtained Rb/Sr 
ages of 377 m.y. and 383 m.y. for these muscovites, 
which sets a minimum age for the pluton as late Early to 
early Middle Devonian. 

West- to northwest-dipping sheeting is well exposed 
in the quarry walls. Note particularly the increased 
thickness of the individual sheets with depth. 
STOP 5a . 

Walk west from the quarry to the banks of the West 
River. The contact of the granite body with the surr- 
ounding Waits River Formation is well exposed here. 
Dikes and sills of granite and aplite are numerous 
within a few hundred feet of the contact and may indicate 
a stoping mechanism for the emplacement of the granite 
pluton. The dikes cross-cut bedding and the principal 
schistosity. Some have a weak foliation roughly parallel 
to the regional schistosity but clearly post-date the 
major deformation. The country rocks near the granite 
have been altered by contact metamorphism, in addition 
to being regionally metamorphosed to the staurolite- 
kyanite zone. 

Return to cars; turn around and retrace route north 
to the main road. 

10.1 Junction with paved road; continue straight (north). 

10.2 STOP 6 . WAITS RIVER FORMATION . Park just beyond the 
entrance to the covered bridge, heading north. 

Outcrops typical of the Waits River Formation in the 
center of the Guilford dome are seen along the east bank 
of the West River. The rocks are interbedded impure 
marbles, calcareous mica schists, and mica schists. 
Most of the minor folds present here are assigned to the 
F2 stage and developed congruously with the large-scale 
recumbent folding. They were refolded into their pre- 
sent attitude by the rising of the Guilford dome. 



2^2 



Return to cars; proceed straight (north) on the 
dirt road along the east side of the VJest River. 

10.7 Junction with road to right; continue straight. 

11.2 STOP 7 . BARNARD VOLCANICS . Park along the road above 
the east end of the old West Duininerston Dam. Climb 
down the steep bank (Use caution.) to the west end of the 
now abandoned dam. 

The Midale Ordovician Barnard Volcanics are exposed 
here in the center of the Fall Brook anticline, which 
forms the core of the proposed recumbent anticline above 
the Prospect Hill recumbent fold (Fig. 1) . At this stop 
the rocks include arophibolites and felsic gneisses. 
Minor amounts of rusty-weathering schist similar to the 
Cram Hill are present along with the Barnard in this 
anticline but have not been designated separately on 
Figure 1. 

Turn around; retrace route south to the covered 
bridge . 

12.2 Covered bridge; turn right; cross the bridge. At the 
west end, turn left (south) onto Route 30. 

12.9 West Dummerston Village. Note Black Mountain and the 

granite quarry to the east across the West River. 

13 3- . . 

, ' , Outcrops of the Waits River Formation. 

13.8 Iron bridge to left; junction of road to the right. 
Continue straight on Route 30. Outcrops of granite in 
the brook to the west. 

15.2 STOP 8 . WAITS RIVER FORMATION ALTERED BY CONTACT 

METAMORPHISM . Park at the side of Route 30 by the large 
road-cut on the right (west) . 

The Waits River Formation in this outcrop is near 
the contact of the Black Mountain Granite. Calc- 
silicates (particularly actinolite and diopside) are 
well developed in the impure marble beds. Diopside has 
not been observed in the Waits River Formation of the 
Guilford dome area outside of the contact aureole of 
the Black Mountain Granite. 

Continue south on Route 30 . 

16.8 Roadmetal quarry in the Waits River Formation to the 
west. 

17.0 Outcrop of Waits River Formation. 

17.7 STOP 9 . GILE MOUNTAIN FORMATION , MARBLE MEMBER . Park at 
left in the pull-off under the 191 overpass. 

Outcrops under the overpass are fairly fresh 
exposures of the marble member of the Gile Mountain 
Formation, metamorphosed to the biotite zone. The 
impure marble beds (already starting to obtain the 
distinctive punky-brown weathering rind) similar to 
those in the Waits River Formation are interbedded with 
phyllites. The percentage of micaceous quartzite beds 



243 



is fairly high here (approximately 15 percent) , as is 
typical of this member. 

END OF FIELD TRIP 

Continue south 1.5 miles to Brattleboro for junctions with the 
major highways. 



Cited References 

Billings, M.P., 1956, The geology of New Hampshire, Part II, 

Bedrock geology: New Hampshire Plan, and Devel. Comm. , 
203 p. 

Doll, C.G., Cady, W.M. , Thompson, J.B., Jr. and Billings, M.P., 
compilers and editors, 1961, Centennial geologic map of 
Vermont: Vt. Geol. Survey, Montpelier, Vt. , 1:250,000. 

Hepburn, J.C., 1972, Geology of the metamorphosed Paleozoic 

rocks in the Brattleboro area, Vermont: Unpubl. Ph.D. 
thesis, Harvard University, 342 p. 

Naylor, R.S., 1971, Acadian orogeny: an abrupt and brief event: 
Science, v. 172, p. 558-560. 

Pettijohn, F.J., 1957, Sedimentary Rocks: 2nd Ed., New York, 
Harper & Row, 718 p. 

Rosenfeld, J.L., 1968, Garnet rotations due to the major Paleo- 
zoic deformations in southeast Vermont: p. 185-202 in 
Zen, E-an, White, W.S., Hadley, J.B., and Thompson, J.B., 
Jr. (eds.) Studies of Appalachian Geology: Northern and 
Maritime, New York, Wiley Interscience Publ. 

Thompson, J.B., Jr. and Norton, S.A., 1968, Paleozoic regional 
metamorphism in Nev; England and adjacent areas; p. 319- 
327 _in Zen, E-an, White, W.S., Hadley, J.B., and Thompson, 
J.B., Jr. (eds.) Studies of Appalachian Geology Northern 
and Maritime, New York, Wiley Interscience Publ. 

Trask, N.J., 1964, Stratigraphy and structure in the Vernon- 
Chesterfield area, Massachusetts, New Hampshire, and 
Vermont: Unpubl. Ph.D. thesis. Harvard University, 99 p. 



245 



Trip B-12 

STRATIGRAPHIC AND STRUCTURAL PROBLEMS OF THE SOUTHERN 
PART OF THE GREEN MOUNTAIN ANTICLINORIUM, 
BENNINGTON-WILMINGTON, VERMONT 

by 

James W. Skehan, S.J.* 



INTRODUCTION 

This field trip is an introduction to several aspects of 
problems that have vexed students of the geology of the Green 
Mountains, the Berkshires and the Taconic Mountains for decades. 
Hitchcock very early (1861) noted that the rock units flanking 
the eastern siae of the Precambrian core of the Green Mountains 
were different from those of its western flank (Fig. 1) . Prindle 
and Knopf (1932) explained this and the juxtaposition of the two 
contrasting sequences by inferring the existence of the Hoosac 
Thrust which they and MacFadyen (1956) mapped as far north as 
heartwellville . They also mapped the "Cambrian outliers" in the 
dominantly Precambrian terrain of the Green Mountain core (Figs. 
1 ana 2) . Skehan (1961 and this paper) extended the Hoosac 
fault northeasterly and infers tentatively that it marks the 
trace of the plane of angular discordance between the Mt. Holly 
Complex and the Cavendish Formation. Dale (1914-16) was the 
first to map this same contact of the Green Mountain core, which 
he referred to the Algonkian, with the younger rocks (Cambrian) 
to the east in Searsburg (Stops 7 and 8) . He regarded this 
boundary as an angular unconformity. The related problem of 
recognizing the source area and mechanism of emplacement of the 
Taconic allochthon has been addressed by many students of Green 
Mountain and Taconic geology. 

Skehan (1953 and 1961) traced rock units mapped by 
Thompson (1950) and Rosenfeld (1954) in the Ludlow and Saxtons 
River quadrangles respectively through the Wilmington area to 
the Massachusetts border. Mapping in adjacent parts of Massa- 
chusetts has been carried out by Pumpelly, Wolff and Dale (1894) , 
Osberg (1950) , Chidester et al. (1951) , Segerstrom (1956) , 
Herz (1958) , Hatch (1967) and Hatch, Stanley and Clark (1970) who 
have traced the units of the Vermont sequence south to Connecticut, 



♦Department of Geology and Geophysics 
Boston College 
Chestnut Hill, Massachusetts 02167 



2i+6 






Fl GURE I 

GEOLOGIC MAP SHOWING THE 
CAVENDISH FORMATION RELATIVE 

TO THE GRECn Mountain 

ANTICLINORIUM AND RELATED 
FORMATIONS 




J.' 



1 cat I DolfOn fm 
' ' (M«n<Jon fm) 



247 



All of these workers recognized that the rocks of the Taconic 
Allochthon (Zen, 1967, Bird, 1969) are similar to those of the 
eugeosynclinal sequence east of the Green Mountains allowing 
for differences in the grade of metamorphism. Several of these 
geologists have research projects in progress which bear on a 
solution to problems of the present field trip. 

The present field trip proposes to introduce the parti- 
cipants to representative rock types of the western Cambrian 
sequence (Stops 1 and 2) and its continuation on the eastern 
flank (Stop 12) as well as to the Precambrian core rocks of the 
Green Mountains (Stops 3, 4, 5, and 7). Additionally several 
of the component stratigraphic units as well as structural 
relationships of the questionable Cambrian sequence of the 
Cavendish Formation of Doll et al. (1961) (Stops 6, 8, and 11) 
to other units will be studied. 

STRATIGRAPHY 

The stratigraphic succession of the area of the field trip 
(Fig. 2) includes the Mt. Holly Complex of Precambrian age, the 
Cavendish Formation including the Wilmington Gneiss of question- 
able Cambrian age and the Dalton and Cheshire Formations of Lower 
Cambrian age and the Hoosac Formation of Cambrian age. 

Mount Holly Complex 

The Mt. Holly Complex (Skehan, 1961, pp. 28-45) forming the 
core of the Green Mountain Anticlinorium consists of several 
units : 

Microcline Gneiss . The largest part of the Green Mountain core 
in the Wilmington-Woodford area is underlain by coarse-grained 
banded biotite-epidote-quartz-microcline augen gneiss. Commonly 
the quartz is blue. This unit is lithologically similar to and 
in many exposures texturally identical with rocks of the Stam- 
ford Granite Gneiss. Except that blue quartz is absent in the 
Wilmington Gneiss, it is otherwise indistinguishable from the 
microcline gneiss of the Mt. Holly Complex (Skehan, 1961, pp. 29-31) 
and the Bull Hill Gneiss of the Cavendish Formation of Doll 
et al. (1961) . 



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GEOLOGIC MAP OF THE WILMINGTON 
WOODFORD AREA 



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Plagioclase Gneiss . (Harmon Hill Gneiss) . Large areas of the 
Green Mountain core are underlain by dark, banded muscovite-biotite- 
epidote-plagioclase-quartz gneiss commonly containing lesser amounts 
of microcline and quartz in layers and pods, as well as beds of 
amphibolite (Skehan, 1961, pp. 31-35). 

Stamford Granite Gneiss . This distinctive rock is a coarse- 
grained porphyritic gneiss with very large rectangular to 
rounded microcline crystals. The finer grained groundmass con- 
sists of blue quartz, albite, microcline, biotite, epidote and 
magnetite. This unit (Doll et al . , 1961) is in many respects 
similar to the Bull Hill Gneiss of the Cavendish Formation. The 
Stamford Granite Gneiss is considered to be probably intrusive 
into the Microcline Gneiss unit (p€mg) and related rocks 
(Pumpelly et al. , 1894) . 

Younger Metasedimentary Rocks . A distinctive sequence is developed 
in the eastern part of the Green Mountain core and consists of 
massive, buff to blue vitreous quartzite, blue quartz conglomerate; 
conglomeratic gneiss composed of angular to rounded microcline and 
granite gneiss pebbles; crystalline graphite-bearing, blue and 
white quartz-rich white gneiss; fine to very coarse-grained calc- 
silicate granulite, and blue and white quartz-plagioclase gneiss. 

Cavendish Formation 

Skehan (1961, pp. 46-65 and PI. 1) mapped the following 
sequence in the area east of the Green Mountain core: the 
Searsburg Conglomerate Member, the Readsboro Schist unit, and 
the Sherman Marble Member of the Readsboro Formation. Additionally 
he mapped the Heartwellville Schist, which is lithologically 
similar to the Gassetts Schist of the Chester Dome, as a separate 
and younger unit. Doll et al. (1961) showed this sequence as 
the Cavendish Formation (Fig. 1) distinguishing the following 
units: the Sherman Marble, the Bull Hill Gneiss and the 
Readsboro-Gassetts Schist. In the present paper for the purposes 
of more general discussions we shall follow the usage of Doll et al. 
and use the term Cavendish to refer to this entire sequence of 
Searsburg-Heartwellville Schist. 

It is useful, however, for detailed discussions of this 
particular area to further subdivide the Cavendish Formation 
of the Wilmington-Woodford area into its generally distinctive 
lithologies even though their stratigraphic position is not 
clear in all parts of the area (Fig. 2)' In the present dis- 
cussion the Wilmington Gneiss, lithologically similar to the 
Bull Hill Gneiss, is considered as closely related to the 
Cavendish Formation and is tentatively included in that 
sequence (Figs. 2 and 3) . 



251 



Wilmington Gneiss 

The Wilmington Gneiss named by Skehan (1961) is of uncertain 
stratigraphic position. It may be Precambrian in age, resembling 
as it does the microcline gneiss sequence of the Mt. Holly 
Complex of the Green Mountain core. On the other hand the 
apparently conformable relationship immediately beneath the 
Hoosac and Tyson Formations along their eastern contact (Fig. 1) 
suggests strongly the possibility that the Wilmington Gneiss may 
be of Cambrian age. The complex and very complicated relationships 
of the Wilmington Gneiss to the members of the Cavendish Forma- 
tion of Doll et aJ. (1961) along the western contact makes a 
decision as to the age of the Wilmington Gneiss impossible at 
this time. 

The Wilmington Gneiss consists of a medium to very coarse- 
grained, well-banded, somewhat foliated biotite-epidote-quartz- 
microcline-augen gneiss. The microcline is gray to pink and 
occurs as lenticular augen and flaser in which the average long 
diameter is about 7 mm. Locally the augen may reach 3 inches in 
length and are usually flattened into the plane of the foliation. 
Quartz rods and linearly aligned streaks of biotite are a common 
feature of the Wilmington Gneiss. 

The Wilmington Gneiss may be the correlative of the Bull 
Hill Gneiss of Doll et al. (1961) an exposure of which is only 
one mile north of and on line with the northernmost exposure of 
the Wilmington Gneiss of the Wilmington quadrangle (Skehan, 1961, 
PI. I) . 

Searsburg Conglomerate Member . The Searsburg Conglomerate Member 
is typically a blue or white quartz, albite and/or microcline- 
pebble conglomerate in a dark biotite-muscovite-carbonate-albite- 
quartz schist matrix. Thin bedded vitreous buff, white and gray 
quartzite in dark mica quartz schist is closely associated with 
the conglomeratic facies. 

Readsboro Schist . The Readsboro Schist as presently understood 
by the writer is indistinguishable in hand specimen or outcrop 
from the Hoosac Formation consisting as it does of gray, brown and 
black, medium to coarse-grained muscovite-biotite-albite-quartz 
schist locally containing variable amounts of chlorite, muscovite, 
chloritoid, paragonite and garnet. Albite megacrysts 2-15 mm. in 
diameter are characteristic of the formation. The Readsboro 
Schist encloses calcite and dolomite marble of the Sherman Member 
whereas no marble beds have so far been recognized in the Hoosac 
Formation. The Hoosac Formation does, however, contain amphibolite 
beds of volcanic origin. These two formations are thus mapped on 
the basis of these differences. 



252 



Sherman Marble Member . The Sherman Marble is a coarse to very 
coarse-grained white, mottled green and gray to pink, quartz- 
calcite marble with coarse crystals of graphite up to 1 cm. in 
diameter; actinolite or diopside-phlogopite-talc calc-silicate 
granulite; and fine-grained quartz-dolomite marble. This marble 
is more commonly enclosed in the albite schist sequence but in 
the northern part of Mount Snow (Pisgah) it occurs in the 
Heartwellville beds. 



Heartwellville Schist . The Heartwellville Schist i 
and possibly the stratigraphic equivalent of the Ga 
of Doll et al. (1961) of the Cavendish Formation. 
Wilmington-Woodf ord area the lower part of the Hear 
Schist consists dominantly of green chlorite-muscov 
gonite-chloritoid) -garnet-quartz schist whereas the 
dominantly coaly-black, rusty weathering muscovite- 
quartz schist. In hand specimen or in outcrop thes 
indistinguishable from their counterparts in the Pi 
and Ottauquechee Formations except that the Heartwe 
characteristically more highly deformed. 



s the lithologic 
ssetts Schist 
In the 
twellville 
ite- (para- 
upper part is 
chlorite-garnet- 
e rocks are 
nney Hollow 
llville is 



Dalton Formation 

The Dalton Formation of the Wilmington-Woodf ord area is 
separated from the overlying rocks of the Cavendish Formation on 
the southeastern flank of the Green Mountain Anticlinorium by the 
Hoosac Thrust and from the Mt. Holly Complex by an angular un- 
conformity. The Dalton consists of thin-bedded schistose 
muscovite-blue quartz quartzite; biotite-albite-quartz schist; 
black chloritoid-muscovite-quartz phyllite (Mendon Formation of 
MacFadyen, 1956 and Skehan, 1961); and microcline-quartz gneiss. 
The Dalton Formation is of Lower Cambrian age since Walcott (1888) 
found fragments of Olenellus about 100 feet above the Stamford 
Gneiss contact near North Adams, Massachusetts in a quartzitic 
graywacke stratigraphically beneath a band of black phyllite 
considered to be the equivalent of the Moosalamoo and Mendon 
Formations. 

Cheshire Quartzite 



The Cheshire Quartzite is stratigraphically above the 
Dalton into which it grades. It is a buff, gray to light pink 
vitreous quartzite consisting of rounded quartz grains commonly 
showing overgrowths of quartz and cemented together by quartz and/ 
or calcite. In many occurrences, the Cheshire shows primary 
sedimentary structures and is generally a ridge-former because 
of its resistance to erosion. 



253 



HOOSAC FORMATION 

The Hoosac Formation (Hoosac Schist of Pumpelly et al . , 
1894) consists of gray, brown and black, medium to coarse- 
grained muscovite-biotite-albite-quartz schists locally con- 
taining variable amounts of chlorite, muscovite, paragonite 
and garnet. Rocks containing appreciable garnet commonly 
weather to a mottled rusty color. Albite megacrysts 2-15 mm. in 
diameter are characteristic of the formation, which is dis- 
tinguished from the overlying Pinney Hollow Formation by the 
presence of more abundant albite megacrysts, its color, and its 
generally coarser and more granular texture. 

The Turkey Mountain Member of the Hoosac Formation (named 
by Rosenfeld, 1954) is typically a dense dark green to black 
amphibolite commonly characterized by rounded to sub-angular 
white, gray, green or dark brown "amygdules" composed of quartz 
and albite commonly with included epidote, hornblende and garnet. 

STRUCTURAL GEOLOGY 

The area of the field trip is the southernmost part of the 
Green Mountain Anticlinorium which plunges south beneath the 
Cambro-Ordovician arenaceous and carbonate sequence of the 
North Adams-Williamstown area. The Cambrian beds of the west- 
ern flank are overturned and in part faulted along high angle 
reverse faults (Fig. 2). 

The Cambrian rocks of the southeastern flank of the 
Green Mountains are truncated by the easterly dipping Hoosac 
Thrust (Fig. 1) . Rocks of the Cavendish Formation lie above 
the Hoosac Thrust and/or the Precambrian-Cambrian unconformity 
along the eastern Green Mountain front. This boundary between 
the Cavendish Formation and the Mt. Holly Complex is now considered 
tentatively by the writer to be a thrust fault since in this region 
the Precambrian beds show a strong angular relationship to the 
Cavendish beds (Fig. 2). Elsewhere in the Green Mountains where 
the Cavendish or the Tyson Formations contact the Precambrian 
rocks, beds on both sides of the contact have been rotated or 
smeared out by tectonic forces into apparent conformability 
adjacent to the boundary. At some distance from the contact, 
however, the angular difference is observable. The presence of 
strong angular discordance close to the contact of the Mt. Holly 
with the Cavendish Formation suggests that the Precambrian units 
have been truncated by thrusting. 

The data presently available allow the following alternative 
interpretations : 



25^ 



(1) The Cavendish Formation, including the Wilmington Gneiss, 
is of Precambrian age; (2) the Cavendish including the Wilmington 
Gneiss is of Cambrian age but older than the Hoosac Formation of 
known Cambrian age and (3) the Cavendish and the Hoosac Formations 
are both of Cambrian age and are coeval facies of each other but 
the Hoosac now bears a thrust or some other complex structural 
relationship to the Cavendish. Skehan in 1961 offered the first 
alternative as his preferred interpretation at that time. Recog- 
nizing that each of these hypothesis are possible, his present 
understanding of the problem leads him now to prefer the second 
or third hypotheses with (3) being favored, although not proven, 
because it helps to explain more satisfactorily our present under- 
standing of the relationship of the Cavendish to the Dalton Forma- 
tion of the southeastern margin of the Green Mountain core as well 
as to the core rocks themselves (Figs. 1 and 2) . 

The fact that the Hoosac Formation (Fig. 3) overlies the 
rocks of the Cavendish Formation with an angular discordance led 
Skehan (1961) to consider these rocks of questionable Precambrian 
age and Doll et al. (1961) to regard them as of questionable 
Cambrian age. 



TRIP LOG 

Bennington may be reached by travelling south from Burlington 
on Route 7 (the shortest distance) or on 1-91 (a faster highway) 
to Brattleboro and driving about 35 miles west on Route 9. 

The primary references for this trip are: 

Skehan, J.W., S.J., The Green Mountain Anticlinorium in the 

Vicinity of Wilmington and Woodford, Vermont : Bull. 17, 
Vermont Geological Survey, 159 p., 1961 ($3.00) . 

, Geologic Map of the Wilmington-Woodford, Vermont Area , 

from Bull. 17, Vermont Geological Survey, 1961 (25<?) . 

Doll et a_l. , Centennial Geologic Map of Vermont , October, 1961 
($4.00) . 

(These three reference materials may be obtained from the 
State of Vermont, Department of Libraries, Montpelier, Vermont 
by enclosing remittance with order.) 

NOTE: Proceed on your own to Stop 1 after which go to Stop 2, 
where the group will meet at 10:00 a.m. for a traverse along 
City Stream. 



255 



Mileage 

0.00 Woodford-Bennington township line on Route 9 east of 
Bennington Center about 3.5 miles. 

0.20 Stop 1 . CHESHIRE QUARTZITE 

A few hundred feet east of the township boundary of 
Bennington and Woodford on Route 9. Park off the high- 
way near Mountain Melody Motel and walk south to the 
outcrop on the west side of the highway. These beds of 
Lower Cambrian Cheshire Quartzite consist of vitreous, 
buff to light pink, cross-bedded quartzite gently folded 
in an open anticline plunging westerly at approximately 
15° . This fold is closely related spatially to but 
disharmonic as regards the major syncline whose south- 
westerly plunging axial trace passes near Woodford Hollow. 

As indicated by sedimentary cross-bedding, these beds are 
right side up. Hand specimen and thin section examination 
of the rock shows rounded grains of detrital quartz. The 
beds of the eastern limb of this syncline rapidly become 
more steeply dipping and are even inverted toward the 
northeast in the direction of the western margin of the 
Precambrian core of the Green Mountains (Fig. 3) , as the 
Cheshire Quartzite beds to the west give way to the 
stratigraphically lower beds of the Dalton Formation. 

Return to cars and drive east on Route 9 . 

0.40 Outcrops of Cheshire Quartzite in the brook on the east. 
Much of the western slope of Harmon Hill to the east is 
upheld by the resistant beds of the Cheshire and Dalton 
Formations. 

1.30 Junction of the Long Trail and Appalachian Trail with 
Route 9 . 

1.70 Junction of Woodford Hollow Road on the north with Route 9. 

2.00 stop 2 . DALTON (MENDON) FORMATION AND MT . HOLLY COMPLEX 

Park cars off the highway near the place where the high- 
tension power line crosses Route 9. Make a traverse on 
foot along City Stream in a westerly direction. This 
stop is an introduction to the Dalton Formation and to 
some of the Precambrian rocks and is designed to illustrate 
the problem of mapping the precise location of the Pre- 
cambrian-Cambrian contact especially where the rocks on 
either side have been smeared into apparent conformability . 
Commonly, however, retrograde metamorphic effects in 



256 



Mileage (cont'd) 

Precambrian rocks of appropriate composition are recog- 
nizable especially in thin sections. Moreover, many of 
the beds of the Lower Cambrian Dalton Formation, especially 
those consisting of vitreous quartzite containing rounded blue 
quartz sand grains and pebbles, are sufficiently distinctive 
to be recognized. The Dalton Formation additionally 
contains biotite-albite-quartz schist, and schistose 
muscovite-chlorite quartzite. In places, however, where 
biotite-plagioclase gneiss and microcline gneiss of 
the Dalton Formation overlies rocks of similar composition 
of the Mt. Holly Complex, from which they were derived by 
erosion, the precise location of the contact may be 
difficult to determine. 

The Precambrian-Cambrian contact at this locality, about 
350 feet west of the high-tension utility line, is placed 
at the western margin of a pyrite-bearing biotite-micro- 
cline gneiss which is closely associated with a chlorite- 
epidote amphibolite bed. The contact is considered to be 
folded or faulted since the rocks just mentioned are 
separated by a band of blue quartz conglomerate of the 
Dalton Formation from pink microcline gneiss to the east 
assigned to the Mt. Holly Complex (Skehan, 1961). 

Proceed east on Route 9 . 

2.95 Pull off the highway at the large roadcuts near Dunville 
Hollow. 

Stop 3 . MOUNT HOLLY COMPLEX 

Large roadcuts on both sides of Route 9 expose tight 
isoclinally folded bands of the dominantly plagioclase 
gneiss sequence of the Mt . Holly Complex of Precambrian 
age (Skehan, 1961, pp. 28-35). A less important component 
of the sequence here consists of microcline-rich bands 
and thin meta-amphibolites. The northeasterly trending 
well-developed folds are characterized by nearly vertical 
to steep westerly dipping axial planes. Post-metamorphic 
faults and shears, although variously oriented, are 
commonly developed essentially parallel to the axial planes 
of the folds (Skehan, 1961, Fig. 6). The second of two 
localities in the Wilmington-Woodford area where an un- 
metamorphosed basalt dike, considered to be of Triassic 
or Jurassic age, has been recognized is at this series of 
outcrops . 

The rocks of the core of the Green Mountain Anticlinorium 
have been affected by both Precambrian and Paleozoic 



257 



Mileage (cont'd ) 

regional metamorphism. Broughton et aJ^. (1962) refer the 
Precambrian metamorphism of the nearby rocks of the 
eastern Adirondacks to a "hypersthene zone" corresponding 
in its mineral assemblages to the higher grade part of the 
sillimanite-K feldspar zone as developed in the Paleozoic 
rocks of New England (Thompson and Norton, 1968) . The 
rock sequence of the Mt. Holly Complex as mapped in the 
Wilmington-Woodford area bears a striking resemblance to 
that of the eastern Adirondacks, due allowance being made 
for the fact that the rocks of the Green Mountain Massif 
have been altered by retrograde Paleozoic metamorphism of 
approximately the biotite and garnet zones. 

The dominantly dark biotite-plagioclase gneisses dip 
steeply to the west. Deformed pink microcline pegmatite 
layers and light gray feldspathic bands reveal that the 
sequence has been subjected to considerable deformation 
by being isoclinally folded. There are many bedding 
plane faults which are recognized as being essentially 
axial plane faults since the beds are so tightly folded. 

Proceed east on Route 9 up the western flank of the 
Green Mountain Anticlinorium . 

3.50 Large roadcut on the left in dark plagioclase gneiss is 
crosscut by folded Precambrian pegmatite. 

3.85 On the right is a sequence of dark migmatitic gneisses. 
The migmatite is of microcline granite and pegmatite. 
Approximate western contact of the Cambrian beds of the 
Woodford "outlier" with the Mt . Holly Complex. Dark 
phyllite is well exposed in City Stream on the south side 
of Route 9 between here and Stop 4 . 

4.50 Black chloritoid-sericite-quartz phyllite of the Lower 

Cambrian Mendon Formation (MacFadyen, 1956; Skehan , 1961; 
and mapped as Dalton Formation by Doll et al. , 1961) in 
City Stream on the south side of Route 9. 

4.70 Stop 4 . DALTON (MENDON) FORMATION 

Park on the north side of the highway. Cross the road 
and examine the fine-grained chloritoid phyllite in the 
outcrops on City Stream. 



258 



Mileage (cont'd ) 

There are several localities in the core of the Green 
Mountain Anticlinorium where isolated outcrops of Lower 
Cambrian rocks of the Dalton Formation (Doll et ai^. , 1961) 
are exposed of which the Woodford "outlier" is the largest 
exposure. It is about 5 miles long and 1 mile wide over 
much of its length. The northeasterly trending Woodford 
syncline is comprised of two major rock, units: (1) the 
black carbonaceous biotite-sericite-chloritoid phyllite of 
the Dalton Formation and (2) the vitreous gray quartzite 
and schistose quartzite which may represent quartzite beds 
in the Dalton (Mendon) Formation. 

The fact that the sequence of the Woodford syncline is 
comprised in large part of dark arenaceous phyllite 
suggests that its environment of deposition was more 
closely related to that of the Lower Cambrian Moosalamoo 
Phyllite (Doll et al. , 1961) than to that of the dominantly 
arenaceous rocks which typify the Dalton Formation. Both 
are considered to be essentially of equivalent age. 

These outcrops at Woodford are about 10 miles north of the 
locality near North Adams, Mass., at which Walcott (1888) 
found fragments of Olenellus mentioned above. 

At this stop note that cleavage to bedding relationships 
are well developed. Cleavage chiefly dips more stee^>ly 
than the bedding. Southeasterly dipping beds reveal that 
the structural analysis , however , fits no simple model of 
a typical synclinal structure developed by compression. 
Although various aspects of the Woodford "outlier" have 
been described by Prindle and Knopf (1932) , MacFadyen (1956) 
and Skehan (1961) it is not definitely known whether these 
rocks are in normal depositional or in a thrust relationship 
to the underlying Precambrian Mt. Holly Complex. 

Return to cars and proceed northeasterly on Route 9 . 

5.00 Near the entrance to the Prospect Mountain Ski area on the 
right, thin bedded, gray northeasterly-dipping sericite 
quartzite beds were exposed in 1959. 

5.35 In Woodford Center near the church on the east side of the 
road folded, gray to black phyllite is exposed, the beds 
having the attitude, N. 75°W., 20°NE. 



259 



Mileage (cont'd) 

5.75 200 feet southwest of the Peter Pan Motel on the left 
folded, thin-bedded quartzite beds crop out having the 
attitude, N.85°W., 35°SW. The folds, displaying a left- 
handed pattern (Skehan, 1961, p. 112sq.) plunge S.35°W. 
at 30° . 

6.20 Big Pond on the left. 

7.00 The divide at the crest of the Green Mountains inter- 
cepts Route 9 approximately at this location. Proceed 
downslope to the east. The topographic relief of the 
crest of the Green Mountains is generally subdued, outcrops 
are sparse and the swamp and forest cover are heavy. 
This condition, which is typical of large tracts in the 
Precambrian core of the Green Mountains, renders geologic 
mapping sufficiently difficult to impede detailed 
mapping and consequently a sophisticated understanding 
of the geology of the core of this massif. 

8.25 Ann Marie's Restaurant -- the only all-weather restaurant 

between Bennington and Wilmington with the possible exception 
of motel-related dining facilities. 

9.25 Stop 5 . VIEW AND PICTURE STOP 

Park on the north side of the highway at an abandoned 
gasoline station and cabins. To the north is a panoramic 
view of the breadth of the Green Mountain Massif with 
one of its highest peaks, Stratton Mountain in the 
Londonderry Quadrangle, visible in the distance. The 
rocks of the Mt. Holly Complex lie to the east of the 
Dalton Formation and Cheshire Quartzite, the ridge- 
formers on the near skyline to the northwest. In the 
far distance to the northwest may be seen Mt. Equinox 
of the Taconic Allochthon. To the east and northeast is 
the very prominent Mt. Snow (Pisgah)-Mt. Haystack Ridge 
comprised of questionable Cambrian metasediments of the 
Cavendish Formation of Doll et al. (1961) . 

Return to cars and proceed east on Route 9 . 

11.40 Junction of Route 9 with Route 8. Proceed south on 
Route 8 . 

11.95 Stop 6 . VIEW AND PHOTO STOP 

Park off the road and out of the line of traffic. Rusty 
weathering calc-silicate granulites are exposed in small 
road outcrops. This stop is near the eastern margin of 
the Precambrian core of the Green Mountains, which is 



260 



Mileage (cont'd) 

bounded on the east by the easterly dipping Hoosac Thrust, 
The intensely deformed rocks of the Cavendish Formation 
rise up in the Haystack Mountain and Mount Snow (Pisgah) 
ridge. Their higher slopes are typically capped by the 
resistant dark muscovite-garnet-chlorite-quartz schists 
(Heartwellville Schisc of Skehan (1961) and Gassetts 
Schists of Doll et al. (1961)). The Harriman Reservoir, 
filling a former river valley in the Wilmington Gneiss, 
may be seen to the east-southeast as viewed along the 
valley occupied by the east branch of the Deerfield 
River. Hogback Mountain on the distant skyline is held 
up by the Pinney Hollow garnet-muscovite-quartz schists 
and the Chester Amphibolite, the Ottauquechee and Stowe 
Formations, the schistose portions of these units being 
nearly identical in composition to rocks of the Caven- 
dish Formation. 

Proceed south on Route 8 . 

13.95 Junction of Route 8 with Sleepy Hollow Road. Farrington 
Cemetery is on the southeast corner of the junction. 
Turn left on Sleepy Hollow Road, and proceed 2 miles 
northeasterly to Bond Brook. Park off the road as best 
you can. 

15.95 Stop 7 . READSBORO AND HEARTWELLVILLE SCHISTS 

Proceed on foot in an easterly direction along the north 
side of the swampy area. The stratigraphic section in 
Bond Brook consists of biotite-muscovite-garnet-albite- 
quartz schists overlain by garnetiferous chlorite- 
muscovite-quartz schist of the Cavendish Formation, 
these being identical in lithology with the Hoosac and 
Pinney Hollow Formations. The main thrust (and/or uncon- 
formity) is probably just west of Sleepy Hollow Road at 
this locality. Return to cars and proceed northerly 
toward Route 9 . 



16.35 Bridge over the penstock aqueduct which carries water 
from Searsburg Dam to Medburyville Power Plant. 

16.55 Junction of Sleepy Hollow Road with Route 9. The trace of 
the boundary between the Mt. Holly Complex and Cavendish 
units (the Algonkian-Cambrian boundary of Dale, 1914-16) 
passes beneath this intersection and follows the trend 
of Route 9 for a few hundred feet. 



261 



iMileage (cont'd ) 

At the junction of Route 9 and Sleepy Hollow Road, turn 
left (west) on Route 9. 

16.75 Turn north on the road to the Searsburg Reservoir and 
park out of traffic. 

Stop 8 . PRECAMBRIAN QUARTZITE AND LIME SILICATE GNEISS 

On the northwest corner of this intersection is a small 
outcrop which together with the rock units at Stop 7 
exemplifies several features typical of the boundary 
between the Cavendish Formation and the well-authenticated 
Precambrian rocks of the Mt. Holly Complex. This outcrop 
of blue-quartz quartzite of the Mt . Holly Complex has 
the attitude N.70°E., 90°. The presence of blue quartz is 
a characteristic feature of a number of the units of the 
Mt. Holly Complex. 

A few hundred feet southwest of this intersection are 
outcrops of rusty weathering calc-silicate granulite 
beds. The east-northeasterly strike of these beds con- 
trasts strongly with the attitude of the overlyim 
Cavendish Formation (Readsboro and Heartwellville Schists 
of Skehan, 1961, pp. 45-63) exposed a few hundred feet 
to the east, whose attitude is N.15°E, 60°SE, and which 
were studied at Stop 7 . 

Two hundred feet downslope to the east of this blue 
quartzite outcrop may be seen the penstock aqueduct, 
the foundation of whose pedestals are on a well developed 
sequence of identical and related kinds of Precambrian 
rocks. Crawl under the penstock at one of the openings 
and proceed on foot in a northeasterly direction to the 
Deerfield River and rock-hop your way to the outcrops 
of dark biotite-muscovite-quartz schist cropping out 
on the east side of the river. These rocks grade up into 
biotite-albite-garnet-quartz schists which in turn pass 
upward within a short distance (Skehan, 1961, Pi. I) into 
the green (continuous with the beds of Stop 7) and black 
quartz-mica schist of the Heartwellville Schist. 

The Searsburg Conglomerate is difficult to find at this 
locality but has been exposed in one outcrop south of 
Searsburg Reservoir and consists of elongate quartzite 
pebbles in a calcite-biotite-chlorite-quartz schist 
matrix. 

Return to cars and proceed north to the Searsburg Dam for 
.7 mile on the unpaved road. Turn around in the field 



262 



Mileage (cont'd ) 

adjacent to the gatehouse at the dam. The Precambrian 
gneisses and schists exposed in the spillway of the dam 
are separated by only 300 feet from the Cavendish 
Schists in the Deerfield River below the spillway. 
Return to cars and proceed south to Route 9 . 

17.9 5 Junction of Route 9 and road to Searsburg Dam. Turn left 
(east) on Route 9. 

18.05 Trace of the Precambrian-Cambrian boundary (noted above 
at Mile 16.55) is approximately at this location. Con- 
tinue east on Route 9. 

19.05 The high ridges to the north of the river and Route 9 are 
the green garnet schist of the Heartwellville units. 

19.35 Bridge over Bond Brook of Stop 7. 

20.25 Large outcrops of black quartz-mica schist of the 

Heartwellville Schist, on the left. The black and green 
beds of the Heartwellville Schist also outcrop from 
mile 20.35 to 20.90. 

21.55 On the left may be seen the high cliffs of Stop 9. 

21.65 Wilmington-Searsburg Township Line. 

21.9 5 Medburyville Bridge. Make a U-turn and proceed west on 
Route 9 0.1 mile and bear right on an unpaved road. 
Proceed 0.35 mile to the old hotel beyond the Wilmington- 
Searsburg Township line and park off the road. 

Stop 9 . HOOSAC FORMATION, SEARSBURG CONGLOMERATE, READS - 
BORO SCHIST, SHERMAN MARBLE AND HEARTWELLVILLE 
SCHIST. 



Excellent exposure of cliffs of albite schist of the 

Hoosac Formation (formerly considered to be Readsboro 

Schist in Skehan, 1961, PI. I) in contact with green and 

black schist unit of the Heartwellville Schist to the 

east. This albite schist is regarded as Hoosac Schist 

since it is now known to contain amphibolite similar to 

the Turkey Mountain Member. Traverse easterly across 

these beds to the contact with the coarse-grained albite 

schist of the Readsboro Schist enclosing layers of calcite 

marble of the Sherman Member. Proceed north-easterly to 

the outcrops of Searsburg Conglomerate exposed northeast 

of Medburyville and pictured in Skehan, (1961, Figs. 13 and 14, 

pp. 46-47 and described on pp. 45-49) . 



263 



Mileage (cont'd ) 

Return to Route 9 and go west 4.20 miles to the junction 
of Sleepy Hollow Road. 

26.15 Turn left on Sleepy Hollow Road. Proceed 2.5 miles to 
the junction of Sleepy Hollow Road with Route 8. 
Farrington Cemetery, the same as at Mileage 13.95, is 
on the left. 

28.7 5 Turn left on Route 8 and proceed south 2.1 miles. 

30.85 Stop 10 . READSBORO SCHIST 

Outcrops of dark muscovite-biotite-albite-garnet-quartz 
schist of the Readsboro Formation (Skehan, 1961, pp. 49- 
57) are exposed in the north fork of the west branch of 
the Deerfield River north of Heartwellville . These out- 
crops are immediately east of the inferred location of 
the Hoosac Thrust. 

Proceed south on Route 8 a distance of 0.55 mile to the 
junction of Routes 100 and 8. Proceed easterly (left) 
on Route 100, 1.2 miles. Park off the highway near Lamb 
Brook 0.1 mile south of Stop 11. 

32.60 Stop 11 . HEARTWELLVILLE SCHIST 

Walk back to the outcrop. Excellent road cuts in the dark 
schist of the Cavendish Formation (Heartwellville Schist, 
Skehan, 1961, Fig. 16, p. 60) at the type locality of the 
Heartwellville. 

3 3.80 Retrace the route 1.2 miles to Routes 8 and 100. Proceed 
south on Route 8 . 

34.00 Heartwellville Center. 

34.70 To the west of the highway in the grove of trees a quartz 
breccia is recognized and interpreted as fault breccia re- 
lated to the Hoosac Thrust. 

35.20 Dutch Hill Ski Area. 

35.80 Heartwellville Lodge to the right. 

36.60 The inferred location of the Hoosac Thrust between Heart- 
wellville and Stop 12 lies west (to the right) of the high- 
way. The ridge to the west is the Green Mountain core 
whose eastern part is flanked by the Cambrian Dalton 



26^* 



Mileage (cont'd ) 

Formation consisting of thin vitreous quartzite beds, 
schistose feldspathic quartzite and biotite-albite 
schist. The ridges to the east are comprised of the 
double decker overthrust sheets of the Cavendish units 
on the lower thrust and the Tyson-Hoosac units on the 
upper thrust. 

39.60 Stop 12 . HEARTWELLVILLE SCHIST, DALTON FORMATION AND 

STAMFORD GRANITE GNEISS. 



Turn right (west) from Route 8 and go 0.7 mile to the 
home of Arthur Lincoln. Park off the road and in his 
yard and proceed up the hill to the large outcrops of 
garnet-chlorite-quartz schist of the Heartwellville 
Formation lithologically identical to the Pinney Hollow 
Formation (Tables 12 and 13, pp. 61 and 63) . Traverse 
this section up slope, (down stratigraphically) to the 
contact of the Heartwellville with the Dalton Formation. 

The Hoosac Thrust is interpreted as bringing the shale 
and graywacke facies of the Cavendish units to a posi- 
tion above the autochthonous rocks of the Cambrian beds 
which are traceable approximately three miles to the 
south to f ossilif erous beds of the Olenellus zone of 
Clarksburg Mountain in North Adams discussed above. 
Proceed westerly to the contact of the Dalton beds with 
the Precambrian Stamford Granite Gneiss . Return to cars 
and return to Route 8 . Turn right and proceed south 
toward Stamford on Routes 8 and 100 . 

41.25 Stop 13 . VIEW AND PHOTO STOP 

A view to the south along the Stamford Valley, underlain 
by Quaternary Alluvium which in turn may be underlain by 
Cheshire Quartzite as well as Cambro-Ordovician carbonate 
beds such as are exposed at Natural Bridge in North Adams. 
The steep western slope of Hoosac Mountain is developed 
above the easterly dipping Hoosac Thrust Fault, the 
trace of which is near the base of the slope. This slope 
may contain the traces of multiple thrusts which have been 
mapped by Norton in the Windsor quadrangle (oral communica- 
tion, 1972) . 

Mt , Greylock, (el. 3,491 ft., the highest mountain in 
Massachusetts) comprised of marble interbedded in albite 
schist and green and dark muscovite-quartz-mica schist, 
looms up directly to the south. The Cheshire Quartzite 
and the Dalton Formation of the autochthonous sequence to 



265 



Mileage (cont'd) 



the west of the viewer may be traced on the skyline in a 
southwesterly direction as they continue around the 
southerly plunging end of the Green Mountain Anticlinorium 
in the vicinity of North Adams and Williamstown. After 
this view, the field trip participants who are going 
south and east have several options. The junction of 
Route 2 and Route 8 is 5.35 miles to the south. The 
New York Thruway may be reached by following Route 2 
west about 50 miles to the vicinity of Albany. The 
Massachusetts Turnpike may be reached by following Route 
2 east to 1-91 at Greenfield a distance of about 35 miles 
(driving time 50 minutes) and going south on 1-91 to 
Springfield. Alternatively Route 2 may be followed west 
to Route 7 south which in turn meets the Massachusetts 
Turnpike at Stockbridge, Massachusetts, about 50 miles 
south of North Adams . 



REFERENCES 

Bird, J.M., 1969, Middle Ordovician gravity sliding in the 

Taconic region, in North Atlantic--Geology and Continental 
Drift : Amer. Assoc. Pet. Geol . , Mem. 12, Marshall Kay, 
editor . 

Broughton, J.G., Fisher, D.W., Isachsen, Y.W. and Richard, L,V., 
1962, compilers and editors. Geologic map of New York, 1961 
scale 1:250,000: New York State Museum and Sci . Service 
Geol. Surv. Map and Chart Series, no. 5 (text, 42 p.). 

Chidester et al^. , 1951, Talc Investigations in Vermont: Prelim. 
Rpt. U.S. Geol. Surv., Circ. 95, 33 p. 

Dale, T.N., 1914-16, Field notes on the Algonkian-Cambrian boundary 
east of the Green Mountain axis in Vermont: Open file in 
U.S. Geol. Surv. Office, Boston, Massachusetts. 

Doll, C.G., Cady, W.M. , Thompson, J.B., Jr., and Billings, M.P., 
1961, compilers: Centennial geologic map of Vermont, scale 
1:250,000. 

Hatch, N.L., Jr., 1967, Redefinition of the Hawley and Goshen 
Schists in western Massachusetts: U.S. Geol. Surv. Bull. 
1254-D, 16 p. 



266 



References (cont'd ) 

Hatch, N.L., Jr., Stanley, R.S., and Clark, S.F., Jr., 1970, The 
Russell Mountain Formation — a new stratigraphic unit in 
western Massachusetts: U.S. Geol. Surv. Bull. 1324-B, 
pp. Bl-BlO. 

Herz, N., 1958, Bedrock geology of the Cheshire quadrangle, 

Massachusetts: U.S. Geol. Surv., Geol. Quad. Map GQ 108. 

Hitchcock, E., et a_l. , 1861, Report on the geology of Vermont: 
Vt. Geol. Surv., 2 vols., 982 p. 

MacFadyen, J. A., Jr., 1956, The geology of the Bennington area, 
Vermont: Vt. Geol. Surv. Bull. 7, 72 p. 

Osberg, P.H., 1950, The Green Mountain Anticlinorium in the 

vicinity of Rochester and east Middlebury, Vermont: Vt. 
Geol. Surv. Bull. 5, 127 p. 

Prindle, L.M. and Knopf, E.B., 1932, Geology of the Taconic 

quadrangle: Amer. Jour. Sci., 5th Ser., vol. 24, pp. 257- 
302. 

Pumpelly, R. , Wolff, J.E., and Dale, T.N., 1894, Geology of the 
Green Mountains in Massachusetts: U.S. Geol. Surv. Mon . 
23, 206 p. 

Rosenfeld, J.R., 19 54, Geology of the southern part of the Chester 
Dome, Vermont: unpub . Ph.D. thesis. Harvard University, 
303 p. 

Segerstrom, K., 1956, Bedrock geology of the Colrain quadrangle, 
Massachusetts: U.S. Geol. Surv., Geol. Quad. Map GQ 86. 

Skehan, J.W., S.J., 1953, Geology of the Wilmington area, Vermont: 
unpub. Ph.D. thesis. Harvard University, 17 2 p. 

, 1961, The Green Mountain Anticlinorium in the vicinity of 

Wilmington and Woodford, Vermont: Vt. Geol. Surv. Bull. 17, 
159 p. 

Thompson, J.B., Jr., 1950, Geology of the Ludlow, Vermont area: 
unpub. Ph.D. thesis, Mass. Inst. Tech. 

, and Norton, S.A., 1968, Paleozoic regional metamorphism in 

New England and adjacent areas, pp. 319-328 in Studies of 
Appalachian Geology: Northern and Maritime , Zen, E., 
White, W.S., Hadley, J.B., and Thompson, J.B., Jr., editors, 
Wiley Interscience. 



267 



References (cont'd ) 

Walcott, CD., 1888, The Taconic system of Emmons: Amer . Jour, 
Sci., 3rd ser., vol. 35, pp. 307-327. 

Zen, E., 1967, Time and space relationships of the Taconic 
allochthon and autochthon: Geol. Soc . Amer., Special 
Paper, no. 97, 107 p. 



269 



Trip B-13 

POLYMETAMOKPHIS^ IN THE RICHMOND ARiiA, VERMONT 

John E, Thresher 

University of Wisconsin-Extension 

SUMMARY 

Rocks in the Richmond Area, Vermont consist mainly 
of wackes and phyllites with minor slates, quartzites, and 
amphibolites. These lithologies are divided into the Rich- 
mond Pond Phyllite and the Huckelberry hill Wacke of the 
Pinnacle r'ormation, the Verdis Montis Amphibolite, and the 
Preston Pond Phyllite and the Duck Brook Wacke of the Under- 
bill Formation, These units are correlated with the pre- 
viously undivided Pinnacle and Underbill Formations in 
adjacent areas. 

Graded bedding was used to indicate the way up 
in the section, which was preserved, along with evidence 
of six deformations. The sequence of deformations, as de- 
du.^ed by comparing the offsetting relationships of structures 
in single outcrops containing more than one structure, indi- 
cates that the area was folded, refolded, cleaved, the clea- 
vage folded, kinked, and jointed, in order of decreasing 
relative age. The outcrop pattern is primarily second fold 
generation. The regional schistosity and the cleavage are 
the most commonly recognized structures. The folding of 
the cleavage and the kinking were minor events which were 
recorded only in the western part of the area, an area in 
which some of the joint planes are filled with basic igneous 
dikes. The first folding is believed to be Taconian, the 
second Acadian, and the kinking related to the Hinesburg 
thrust to the west of the area, 

Recrystallization was associated with periods of 
folding and cleavage formation. The rocks were metamor- 
phosed at the greenschist facies level each time, with the 
formation of biotite associated with the second period of 
folding being the highest level attained, A correlation of 
structure and metamorphism is combined to produce a tectonic 
sequence of deformational events for the Richmond area. 

The purpose of this trip is to examine polymeta- 
morphic assemblages in the Huckelberry Hill Wacke, Since _ 
many of the relationships between structure and metamorphism 
can be seen in hand specimens of this unit, it is suitable 
for field analysis. The wacke is dark green or drak gray 
•in color depending upon whether pyrite + magnetite or magne- 
tite along is present as an accessory phase. This difference 
"cverned the mineral assemblages associated with the fourth and 
1 inal recrystallization. The three earlier recrystallizations, 
* ov/over, appear to have produced similar mineral assemblages 
throughout this unit. 



272 



Environmental Geology Cover page: Upper: Sanitary landfill, 

Randolph, Vermont. Lower: Resistivity study, Hinesburg delta, 
Hinesburg, Vermont. Photos by Arthur Huse, UVM Geology Depart- 
ment. 



273 

EG-1 
MOUNT MANSFIELD TRAIL EROSION 



Computerized statistical analysis of hiking trail ero- 
sion on a scenic area along the Green Mountains. Geology and 
vegetation of mountainous areas and their relationship to human 
recreational activity. 



(The complete text of this paper will be available at 
the meeting in October.) 



276 



"Of the origin of Tah - wah - bebe -e Wadso — The Saddle 
Mountain — which became Lion Couchant, then Camel's Rump, later 
Camel's Hump; and its companion, Mount Mansfield, the Reverend 
Perrin B. Fiske speculated: 



The Camel's Hump is there on high. 

His head the sages think. 

Is by the river's brink, where once 

He ran to kneel and drink. 

But stumbling in his thirsty haste 

He threw his rider high. 

And there lies Mansfield as he fell 

A-staring at the sky." 



From: Hill, Ralph Nading, 1949, The Winooski, Heartway of 
Vermont: Rinehart & Company, Inc., New York, p. 242. 



JkM. 



277 



Trip EG -2 

FEASIBILITY AliD DESIGN STUDIES: CHAI4PLAIN VALLEY SANITARY LANDFILL 

bv 

* 
W. Philip Wagner and Steven L. Dean 

INTRODUCTION 

In theory, solid waste disposal in Vermont has progressed 
from dumps to sanitary landfills, but in practice the differences 
between the two often are obscure. According to a recent review, 
"Over 90% of the small towns in Vermont dispose of their refuse in 
open dumps or substandard landfills" (Report of the Governor's Task 
Force, 1970) . There is growing evidence that some of the better 
sanitary landfills are polluting (Thompson and Costello, 1972; Wag- 
ner ct al . , 1971; Wagner and Thompson, 1971). Although recvcling 
eventually may solve the solid waste problems, sanitary landfill- 
ing is the only practical method presently available for Vermont. 

This report is intended to illustrate that: 

- knowledgeable landfill location and site evaluation can 
greatly reduce the chance of environmental degradation... 

- sanitary landfills are not merely covered dumps, but in 
fact represent specially designed systems... 

- short of recycling, there can be such a thing as a ''goca 
landfill", even in Vermont. 

This is not a comprehensive account of all aspects of landfills. 
Emphasis is focused on pertinent, but commonly ignored geological 
and hydrogeological factors. The bibliography includes all nubli- 
cations reviewed in this project. 

LANDFILL LOCATION 

Much of the work presented here stemmed directly from a re- 
quest from Paul Casey, Hinesburg Sand and Gravel Co., Inc., for 
help in designing a landfill that absolutely would not degrade the 
environment. Thus, the problem began, at least in a general wav , 
with a given location near Burlington. For a private operator, a 
public official, or a planner faced with the initial problem of 
locating a suitable landfill site, the procedure to be followed 
would be much the same as used here. The Appendix includes a 
check list for evaluation of different sites. The following dis- 
cussion deals with environmental guidelines for landfills. 
* 

University of Vermont. 



278 



Sanitary landfills can be located in almost any place, but 
if financial costs for protecting the environment are to be mini- 
mized, it is desirable to recognize and take advantage of certain 
natural characteristics of the land. The problem, simply stated, 
is to identify criteria for locating landfills in Vermont. If 
meaningful, such criteria will aid rather than hinder landfill 
development. Sound guidelines for locating landfills will make 
good economic as well as environmental sense. 

The logical way to develop criteria is to consider previous 
studies on the subject. Literature dealing with sanitary landfills 
is extensive. In some places certain criteria have been developed, 
but most publications relate studies of individual landfills. 
Some aspects of studies elsewhere may not be directly applicable to 
Vermont due to differences in topography, climate, soils, or rocks. 
On the other hand, similarities in reports from diverse places in- 
dicate that there are some universal "truths" that cut across pol- 
itical boundaries. By combining information from various studies 
it is possible to develop criteria for locating landfills accord- 
ing to substrate and cover materials. Depending on whether the 
substrate is relatively permeable or impermeable, the following 
criteria can be identified: 

1. Permeable substrate, generally sand and gravel, with: 

a) minimum 1000 feet to nearest perennial stream 

b) minimum 30 feet of dry substrate below land- 
fill base 

c) maximum 10% slope 

2. Impermeable substrate, generally certain glacial tills 
and some lake or marine bottom sediments, with: 

a) minimum 200 feet to nearest perennial stream 

b) minimum thickness of 5 feet of substrate below land- 
fill base 

c) maximum 10% slope 

d) minimum 5 feet of dry , permeable material overlying 
impermeable substrate 

e) leachate control and treatment 

Tlie current trend nationally is toward sites with impermeable sub- 
strata. In such sites leachate is either prevented from leaving 
the landfill, or moves at such low velocities that it undergoes 
optimum purification by chemical and biochemical reactions, fil- 
tering, and dilution. Landfills with permeable substrate may be 
suitable for certain kinds of waste material not likely to cause 
environmental degradation. 

As for cover materials, both impermeable and permeable soil 
covers have been used elsewhere. The former has the advantage of 
repelling surface water, thereby minimizing leachate generation, 
but retarding gas release. The latter promotes upward escape of 
gas but also allows for surface water infiltration leading to in- 
creased leachate production. A formula of 80% well-graded gravel. 



279 



10-15% sand, and 5-10% fines provides a relatively impermeable 
cover that, with specially designed gas vents, offers optimum 
conditions for controlling leachate production, gas diffusion, 
rodents, flies, and frost heaving. In addition, such material 
can be compacted and can support heavy vehicle traffic. Thus, 
site location considerations should include, in addition to sub- 
strata conditions, the availability of sufficient volumes of cov- 
er materials which will offer the benefits outlined above. In 
Vermont, the natural deposits most closely resembling the ideal 
cover material are certain glacial tills and glacial gravels. In 
most cases, however, cover material probably will have to be spe- 
cially prepared by mixing materials of different grain size. 



SITE EVALUATION 

Location, Topography, and Drainage ; The proposed site in 
question involves about 25 acres of relatively impermeable soils, 
approximately 3 1/2 miles southeast of Hinesburg Village, in the 
Town of Hinesburg (Figure 1) . The site is situated in the foot- 
hills of the Green Mountains in an area of gently rolling top- 
ography. Elevations of the land surface at the vicinity of the 
site range from below about 500 feet to about 420 feet over long, 
gentle slopes (Figure 2) . 

Drainage in the area is westerly as part of the Lewis Creek 
drainage basin. Hollow Brook, the perennial waterway closest to 
the site, is almost 2000 feet to the north. A small intermittent 
stream is located along the south and west margins of the landfill 
area. Although the surface waters in Lewis Creek are intended to 
be classified as "B" (suitable for drinking with treatment) , sam- 
ples taken in 1956 indicated class "C" (unsuitable for drinking) 
coliform levels (Vermont Department of Water Resources, 1968, p. 
16) . 

Elevations at the landfill site are above flood levels from 
any streams. However, Hollow Brook to the north is actually at a 
higher level than the site. Surface flooding of the site from 
Hollow Brook is prevented by extensive, high deposits of gravel 
between the landfill site and Hollow Brook. These deposits should 
be partially preserved from commercial gravel excavations to pre- 
vent southward diversion of Hollow Brook through the landfill site, 

Soils : From the point of view of soils and topography 
throughout Chittenden County, the South Hinesburg area is consid- 
ered as having good potential for sanitary landfills (Sargent and 
Watson, 1970) . However, the detailed soils map of the area by the 
Soil Conservation Service (Figure 3) shows some limitations for 
landfills. A summary of the pertinent aspects is presented in 
Table 1. 



280 







Figure 1: (top) Location of site on County Highway Hap (diagonally- 
ruled circle. s| 

Figure 2: (bottom) Topography at site and vicinity (diagonally- 
ruled circle) . 



281 




Figure 3 



Detailed soils map of tho l^.nclfiU are?, by Soil Consorvatior 
Service. Units are exolained m Tabic 1. TH = test hole- 
G = geophysical test. 



282 



Slope (%) 


Limitations 


— — _ 


high water table 


20-30 


steep slopes 


0-5 


high water table 


0-3 


high water table 


3-8 


low permeability 




and strength 


12-15 


high water table 


2-6 


high water table 


) 5-12 


steep slope 



Table 1: Soils at the landfill site and vicinity. 

Soil Type (map symbol) 

AuGres fine sandy loam (Au) 
Colton and Stetson soils (CsD) 
Duane cind Deerfield (DdA) 
Enosburg and Whately (EwA) 
Hinesburg fine sandy loam (HnB) 

Munson and Belgrade silt loams (Mud) 
Munson and Raynham silt loams (MgB) 
Stetson gravelly fine sandy loam (StB) 

In the immediate area of the landfill the dominant soil types have 
problems with seasonal high water tables due to low permeability. 
It should be pointed out that such water tables are "perched" types 
due to the retention of precipitation at and near the surface. 
This problem, unlike deeper ground water, can be overcome easily 
by appropriately designed drainage controls. 

The amount of water that collects on the land surface at the 
site can be estimated. •'• Due to the highly permeable character, 
the irregular topography, and low ground water table of gravel 
areas adjacent to and uphill from the site (north and east) , sur- 
face waters readily infiltrate the gravelly soils or are naturally 
diverted around the site. Thus, the water that collects on the 
impermeable surface at the site is derived primarily from rain and 
snow directly on the site itself. Of the 30-40 inches of annual 
precipitation in the area, about half is lost by evapotranspira- 
tion. The remaining 15-20 inches, representing 31-42 acre-feet 
over the 25 acres of the site, constitutes surface runoff. Due to 
the seasonality of precipitation and evapotranspiration, larger 
amounts of water are expectable during the spring and fall than 
other periods. The amount of water at the site due to snow melt 
is about 10 inches (water equivalent) , or nearly 21 acre-feet, very 
little of which is lost by evapotranspiration. The non-snow pre- 
cipitation of 20-30 inches, on the other hand, is reduced by about 
90% by seasonally high evapotranspiration to about 2-3 inches or 
about 4-6 acre-feet. The problem of poor surface drainage is at 
least three orders of magnitude greater in the spring than in the 
rest of the year. This can be reduced by snow removal to negligi- 
ble amounts. During the remainder of the year slightly less than 
2,000,000 gallons of water will enter the site. Initially, most 
of this water will be diverted westward, away from the landfill 
operation. 

Geology : Bedrock in the area is completely buried by uncon- 
solidated materials. Regional geologic studies, however, indicate 
that the buried bedrock consists of the Underhill formation, a 
micaceous schist. The schist is impervious to water except where 

^ Robert Hendricks, U.S.D.A., provided meteorological data and 
helped with estimations. 



II 
I 



283 



joints (cracks) have developed. In this region joints are less 
abundant than elsewhere. As a result, ground water movement in 
bedrock is highly restricted and, therefore, less sensitive to 
pollution than usual. 

The deposits overlying bedrock largely determine the envir- 
onmental suitability of the landfill. General geologic informa- 
tion shows the landfill site is in an area of former lake bottom 
where fine-grained sediment was deposited. The gravel deposits 
immediately north of the site are in a deltaic deposit formed in 
the same lake. East of the site at the surface, and buried be- 
neath much of the fine-grained sediment at the site itself, are 
gravel deposits produced by the ice sheet in the area. Over much 
of the area glacial till is expecteible beneath the gravels and 
fine-grained sediments, and directly over bedrock. 

Detailed information on subsurface geologic conditions has 
been obtained by drilling and by geophysical (seismic and resis- 
tivity ) testing. Information from the tests, which are located 
on Figure 3, is presented in cross-sections in Figure 4. Bedrock 
ranges from 50 to 100 feet beneath the land surface, with greater 
depths in the deltaic deposits north of the landfill site. The 
slope of the bedrock has a distinct westerly and southwesterly 
component, somewhat similar to the present land surface. Buried 
till is present in the eastern part of the area (profile A, Figure 
4) at sites THl-Gl and G3, but is not evident at other sites. A 
thick gravel layer is the dominant feature of the subsurface mat- 
erials. This gravel is overlain in most places at the site by up 
to 20-30 feet of the fine-grained lake sediments. 

Ground Water ; As previously mentioned, perched water col- 
lects at and near the surface of the lake sediments at the site. 
Whether or not this constitutes ground water is a semantic and acad- 
emic question. Such near-surface waters are not generally used for 
water supplies. As pointed out previously, this water can readily 
be controlled. Water at greater depths in the ground, on the 
other hand, constitutes a natural resource that must not be contam- 
inated by the landfill. Testing has shown that the gravel deposit 
buried beneath the fine-grained surface sediments contains ground 
water and, therefore, constitutes an aquifer. Water table slopes 
(Figure 4) indicate that recharge to this aquifer is provided by 
Hollow Brook (an influent stream) and undoubtedly to a lesser ex- 
tent by percolating surface waters in the gravel deposits north 
and east of the site. Ground water movement is westerly to south- 
westerly. Changes of the level of the water table are expectable 
with time, primarily at different seasons of the year. Measure- 
ments of the water table depth in the test holes show only slight 
changes to date. Based on statistical analyses^ of four gravel 
wells monitored by the Vermont Department of Water Resources, we 
have projected probable future changes in the water table in the 
test holes. These projections show that ground water remains well 
below the surface at all times, with seasonal fluctuations no more 

^ Resistivity data provided by Arthur Huse. 
Statistical work by Steven Pendo. 



284 



than about 10 feet. 

From the viewpoint of ground water contamination it is im- 
portant to note that the landfill site is not a recharge area 
for the gravel aquifer. Significant downward movement of leach- 
ate through the fine-grained sediment is not expectable. Perco- 
lation tests in such materials have shown exceedingly low rates 
of movement (Mullen, 1972; Waite, 1971). Thus, with special pre- 
cautions to control and monitor leachate movement, ground water 
contamination can be prevented. 

Miscellaneous : A variety of aspects deserve brief mention. 

1. Biota: The immediate area of most of the landfill site 
has been actively farmed until the present time, so that no nat- 
ural plant species are endangered. Along the periphery of the 
landfill on all but the north and northwest sides are common spe- 
cies of mixed hardwood and softwood trees, grasses and sedges. 
Animals in the area are likewise common species. No damage to 
ecologically fragile or otherwise unique biota is likely to occur. 

2. Forest reserves: The landfill site mostly lacks timber 
except along the eastern fringe. The site is on the margin of the 
productive forest area of the Green Mountains, with soils rated 
fair at best for potential forest productivity (Gilbert, 1970) . 

3. Agricultural reserves: According to Carlson et al. (1970, 
p. 3) , the landfill area is in a classification noted as ^.the 
least suitable of all land now being used for agriculture in the 
county." Moreover, the area's present agricultural land use is 
considered by the same authors to be marginal to poor. 

4. Natural areas: The site has no known value as a natural 
area deserving protection for biologic, geologic, archaeological, 
or other natural characteristics. 

5. Aesthetics: View of the landfill site is blocked by high 
banks of gravel to the north, by the Green Mountains and tree cov- 
er to the east, and by a fringe of trees along the south and south- 
west margins. The only open view of the site is from the north- 
west and west. This will be remedied by tree plantings. Thus, 
complete privacy for the operation will be provided from all pub- 
lic vantage points. 

6. Erosion: Erosion is not a problem in the area of fine- 
grained soils due to the soil cohesion and particle size. In gra- 
vel soil areas, only artificial slopes greater than about 65% show 
evidence of instability and erosion. 



285 



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286 



DESIGN AND OPERATION 

The sanitary landfill here proposed involves a combination 
of trench and area methods, utilizing impermeable base and cover 
materials, and artificial leachate and gas movement controls. 
Diagrammatic aerial and cross-section views of the landfill are 
given in Figure 5. Initially » non-bulky refuse will be placed in 
a trench system oriented nortr -south. After the trenching opera- 
tion is completed, a superposed area-fill type of landfilling will 
commence. Based on an average total fill thickness of 50 feet 
with a waste to cover ratio of 4:1 and a 1000 Ib/yd^ density for 
compacted fill, the anticipated life span of the operation is 
about 22 years per 40,000 persons served. Bulky, non-putrescible 
items will be handled separately in the areas shown in Figure 6. 

Cover material for the operation will be an artificially 
pre-mixed formulation of 80% well-graded gravel, 10-15% sand and 
5-10% fines. Sand and gravel for the cover will be taken from 
the nearby commercial operations. Fines for the cover material 
will be obtained from the silt-clay layer at the site itself. 
Sufficient volumes of cover material are available for at least 
100 years operation per 40,000 persons. 

Effluent Control : Due to the impermeable nature of the 
cover, little or no leachate is exnected from the landfill. How- 
ever, special design conditions are recommended to insure that 
no ground or surface water pollution can be caused by leachate. 
Fill-trench floors in the fine-grained sediment will be sloped 
and veneered with gravel to direct drainage from the fill-trench 
system to a filter-storage trench on the northern margins of the 
fill. Berms will divert surface waters away from the site and 
away from the filter-storage trench. 

A pump system will draw leachate through an underdrain in 
the filter-storage trench and transfer the leachate to steel sto- 
rage tanks located at the western end of the site. The landfill 
operation will begin at the eastern margin of the landfill-trench 
system. At first only a small portion of the total site will be 
developed, the actual size depending on the size of the popula- 
tion served. Assuming v/astes are collected for 40,000 persons, 
the trenching required will involve about 3 acres per year. The 
volume of leachate, based on infiltration of rain and snow remov- 
al, should be less than 250,000 gallons the first year and 500,000 
gallons the second year. The steel tanks will hold an aggregate 
volume of 30,000 gallons, which when combined with the filter- 
storage trench capacity of about 500,000 gallons, will provide 
storage in excess of the amount expected for the first and second 
years of operation. At the end of that time sufficient data will 
be available to plan for increased storage capacities as necessary. 

Depending on the chemical quality of the leachate collected, 
it may be pumped from the steel tanks to the distribution line of 



287 




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288 



the filter-storage trench for filtration (Figure 5) . Alterna- 
tively, the leachate may be chemically treated. Release of 
treated leachate will be effected by pumping it to the gravel 
area northeast of the landfill. Here the large thickness of dry 
gravel will provide further filtering. 

Gas Control ; Gases produced in the landfill will be trans- 
mitted through the gravel on trench floors in an up-slope direc- 
tion toward the eastern and southern margins. There the gases 
will be released to the atmosphere through the gravel vent. 

Monitoring : Although elciborate steps will be taken to 
guard against water pollution, monitoring stations are to be used 
for periodic sampling of natural surface and ground waters at 
sites shown on Figure 5. Ground water will be monitored by samp- 
ling from perforated pipes installed in the test holes. Periodic 
checks of the ground water tcible elevation will be continued. 
Finally, close supervision will be made of the leachate quantity 
and quality in the steel tanks and in piezometers installed in 
and below the filter-storage trench. 

Analysis of the biochemical quality of ground and surface 
waters will be guided by the quality of the leachate. Samples 
from all check points will be taken at least three times per year 
and at more frequent intervals from leachate storage facilities 
as required. 

Miscellaneous ; 

T~. Litter control: Snow-fencing erected on periphery of 
trench in operation. 

2. Vandalism control: Two full-time attendants during op- 
eration; cyclone fence along periphery of landfill with locked 
gates during non-operation hours. 

3. Fire control: In addition to benefit of cover material, 
pond adjacent to landfill can be used for water supply for fire 
fighting. 

4. Access roads: All-weather, 24 foot wide, asphalt sur- 
facing with grades less than 7%. 

5. Buildings: Existing weigh scale station, and mainten- 
ance and vehicle storage sheds will be utilized (Figure 5) . 

6. Personnel facilities: Toilet and water supply facili- 
ties available in scale house. 

7. Clearing and grubbing: Not necessary. 

8. Rules and regulations will be posted as follows: 

a. No private use. 

b. All operations supervised during specially designat- 
ed times. 

c. No salvaging without permission of owner. 

9. Method of handling and compacting waste: Refuse will be ij 
dumped at toe of working face and spread to a 1000 lb. density 
with continuous spreading and compacting. 

10. Site reclamation: Soil cover material at site will be 
stockpiled along margins of site for resoddinq upon completion of 
landfill. 



289 



REFERENCES CITED 

Bergstrom, R. E. , 1968, Disposal of wastes: Scientific and admin- 
istrative considerations: 111. Geol. Surv. ; Envir. Geol. Notes 
Number 20, 12 p. 

Brunner, D. R. , and Keller, D. J., 1971, Sanitary landfill design 
and operation: U. S. Envir. Protection Agency, report SW-65ts, 
149 p. 

Carlson, R. L. , Eddy, D. K. , Snyder, J. P., and Thompson, N. C, , 
1970, Agricultural land classification, Chittenden County: 
Lcike Champlain Basin Studies, Study No. 12, 5 p. 

Cartwright, K. , and Sherman, F. B., 1969, Evaluating sanitary 
landfill sites in Illinois: 111. Geol. Surv., Envir. Geol. 
Notes, Number 27, 15 p. 

Chittenden County Regional Planning Commission, 1970, Solid waste 
disposal: Completion report, Vt . P-43, 61 p. 

Coe , J. J., 1970, Effect of solid waste disposal in groundwater 
quality: Jour. Amer. Water Works Assoc, p. 776-783. 

Emrich, G. H., and Landon , R. A., 1969, Generation of leachate 
from sanitary landfills and its subsurface movement: reprint 
from talk given at the Annual Northeastern Regional Anti-Pol- 
lution Conference, Univ. of Rhode Island, July 1969, 14 p. 

Flawn, P. T. , Turk, L. J., and Leach, C. H. , 19 70, Geological 

considerations in disposal of solid municipal wastes in Texas : 
The Univ. of Texas: Bur. of Econ. Geol., Geol. 67. 70-2, 22 p. 

Freeze, R. A., 1972, Subsurface hydrology at waste disposal sites: 
IBM, Jour, of Res. Develop, v. 16, number 2, p. 117-129. 

Gilbert, A. H. , 1970, Forest resources of Chittenden County: Lake 
Champlain Basin Studies, Study No. 5, 7 p. 

Hughes, G. M. , 1967, Selection of refuse disposal sites in north- 
eastern Illinois: 111. State Geol. Surv., Envir. Geol. Notes, 
Number 17, 18 p. 

, 1972, Hydrogeological considerations in the siting and de- 

sTgn of landfills: 111. Geol. Surv., Envir. Geol. Notes, Num- 
ber 51, 21 p. 

, Landon, R. A. , and Farvolden, R. N. , 1971, Summary of 

findings on solid waste disposal sites in northeastern Illi- 
nois: 111. State Geol. Surv., Envir. Geol. Notes, Number 45, 
25 p. 



290 



Jewell, W. J., 1971, A proposed system for Chittenden County re- 
gional solid waste management: Plan submitted to Chittenden 
County Regional Planning Commission, 18 p. 

Kessler, M. Z., 1970, Sanitary landfill: a selected list of ref- 
erences: Council of Planning Librarians, Exchange Bibliog. 
146, 15 p. 

Lessing, P., and Reppert, R. S., 1971, Geological considerations 
of sanitary landfill evaluations: W. Va. Geol. and Econ. Surv. , 
Envir. Geol. Bull. Number 1, 34 p. 

Mullen, John, 1972, Environmental geology of Milton, Westford and 
Underhill, Vermont: M. S. dissertation. University of Vermont, 
in preparation. 

Pawlowski, T., 1968, Sanitary landfill: U.S.D.A. Soil Con. Serv. , 
Tech. Notes, Soils-Vt.-l, 3 p. 

, 1969, Solid waste disposal: U.S.D.A. Soil Con. Serv., Tech. 



Notes, Soils-Vt.-2, 6 p. 

, 1970, Sanitary landfill information: U.S.D.A. Soil Con. 



Serv., Tech. Notes, Soils-Vt.-3, 5 p. 

Report of the Governor's Task Force, 1970, Solid waste management 
in Vermont: Office of the Governor, 75 p. 

Sargent, F. O. , and Watson, B. G. , 1970, Soils: Lake Champlain 
Basin Studies, Study No. 4, 4 p. 

Schneider, W. J., 1970, Hydrologic implications of solid-waste 
disposal: U. S. Geol. Surv., Circ. 601-F, 10 p. 

The Volunteer Technical Committee, 19 71, Proposals for solid 

waste management in Chittenden County: Chittenden County Re- 
gional Planning Commission, 24 p. 

Thompson, R. , Jr., and Costello, E. J., 19 72, Some chemical para- 
meters of the effluent from the Essex Sanitary Landfill: Un- 
published report at the University of Vermont, 16 p. 

Vermont Department of Water Resources, 196 8, Report on water qual- 
ity and pollution control of Lake Champlain and minor tributar- 
ies, Vermont, 21 p. 

Wagner, W. Philip, and Thompson, R. , Jr., 1971, Preliminary chem- 
ical analyses of streams in the vicinities of five sanitary 
landfills, Chittenden County, Vermont: Unpublished report at 
the University of Vermont, 3 p. 

, et al., 1971, Analysis of selected landfills in Chittenden 



( 



County: Unpublished report at the University of Vermont, 9 p. 



291 



Waite, B. A., 1971, Environmental geology of the Huntington Val- 
ley, Vermont: M. S. dissertation. University of Vermont, 
45 p. 

Wilcomb, M. J., and Hickman, H. L. , Jr., 1971, Sanitary landfill 
design, construction, euid evaluation: U. S. Envir. Prot. 
Agency, 11 p. 

Zanoni , A. E. , 1971, Groundwater pollution from sanitary land- 
fills and refuse dump grounds - a critical review: Wis. Dept, 
of Nat. Res.; Research Rept. 69, 4 3 p. 



292 



APPENDIX: Site Evaluation Considerations for Landfill 

Location 



Economic Factors 



Initial- 



Annual- 



Other- 



Social Factors: 



acreage 

estimated cost per acre 
estimated access road cost 
estimated site clearing cost 
estimated site modification cost 
estimated building cost 
estimated engineering costs 
estimated equipment costs 
estimated fencing costs 



salaries and benefits 

equipment operation 

maintenance and repair 

snow removal 

depreciation 

amortization of initial costs 

administrative overhead 

cost per capita 



reclamation 

recycling-distance from population centroid 



prevailing winds (incineration; dust; odors; noise) 

aesthetics 

present landuse on site 

present landuse adjacent to site 

landuse plans and zoning 

fire protection 

traffic flow congestion and safety 

road conditions leading to site 



Environmental 



site volume 

site longevity 

substrate character and thickness 

cover material character and volume 

bulky item space 

distances to perennial streams, and floodplains 

slope 

groundwater depth and flow direction 



293 



E nvironmental : (continued) 

gas control 

surface water control 

distance to nearby wells 

monitoring 

near present or future sewage treatment plant 





glacial geology 







fl 




fe.- 



•■i5-.*^ 



296 



"Of all the phenomena of drift none have been more difficult 
to explain by any theories in vogue among geologists, than these 
trains of angular bowlders. To make water the sole agent, as some 
theories' do, is the most unsatisfactory; for this could not alone 
have torn the blocks from their parent bed, and if it had been 
able to carry them forward at all, it must have rounded them. 
The most plausible resort would be to glaciers ; but the nature 
of the surface over which the trains have been strewed, forbids 
the idea of a glacier. Common icebergs are no more satisfactory; 
but if we suppose islands capped with ice, and this occasionally 
torn up by the waves, and carried forward with fragments of rock 
in their under side, torn off from the islands and dropped along 
the way, or perhaps ice-floes in like manner frozen to the shore 
and torn off and urged along the coast, there is some plausibility 
in the explanation." 

Edward Hitchcock, 1861 

Geology of Vermont, v. 1, p. 65. 




INDEX MAP SHOWING THE BURLINGTON DRIFT BORDER IN 
THE MONTPELIER REGION 

1 ) BURLINGTON DRIFT 



MORAINES OF BURLINGTON DRIFT 



Kv- SHELBURNE DRIFT 



MORAINES OF SHELBURNE DRIFT 



I I KAME MORAINE 

j/' STRIAE 

^^ FABRIC OF SURFACE TILL 

^r FABRIC OF SUBSURFACE TILL 



Figure 1. Map showing the Burlington drift border in central 
Vermont (from Stewart and MacClintock, 1969, fig. 15, published 
by permission of Dr. Charles G. Doll, Vermont State Geologist) 



297 

Trip G-1 

GLACIAL HISTORY OF CENTRAL VERMONT 

by 

Frederick D. Larsen , Department of Geology 
Norwich University 

Introduction 

The area traversed on this field trip lies on the Barre , 
Fast Barre, and Montpelier 15' U.S.G.S. topographic maps in 
central Vermont. The terrain is underlain by eugeosynclinal 
rocks which range in age from Ordovician to Devonian. The 
rocks were tightly folded and intruded by granite during the 
Acadian orogeny 380 million years ago (Naylor, 1971). Erosion 
has produced, over much of the area, a crude trellis drainage 
pattern which is characterized by alternating linear ridges 
and subsequent valleys which trend north-northeast. Drainage 
passes via the Stevens Branch and the Dog River northward into 
the V/inooski River, a major superposed stream, which flows 
west-northwest through the Green Mountains to Lake Champlain. 

During the Pleistocene central Vermont was probably com- 
pletely covered several times by continental ice sheets, how- 
ever, there is no clear evidence which supports multiple gla- 
ciation as it is known in the Midwest. The last ice sheet 
reached a maximum extent about 19,000 to 20,000 years ago on 
Martha's Vineyard (Kaye, 1964). Near Middletown, Conn., a re- 
advance of the ice occurred before 13,000 years ago (Flint, 
1956), and the Highland Front moraine was constructed in 
southern Quebec about 12,700 years ago (Gadd, 1964). These 
facts have led Schafer (1967) and others to conclude that 
retreat of the active ice margin in northern New England 
was very rapid (1000 ft/yr) and that removal of the ice took 
place by regional stagnation or downwasting. Lack of moraines 
and ice-shove features in central Vermont implies that down- 
wasting was the dominant process during deglaciation. 

Recently, the work of Stewart (1961), and Stewart and 
MacClintock (1964, 1969) has resulted in the controversial 
identification of three drift sheets in Vermont. From oldest 
to youngest they are: (1) Bennington drift, (2) Shelburne 
drift, and (3) Burlington drift. Separation of the drift 
sheets was made on the basis of striations and till-fabric 
studies which indicate that the Bennington and Burlington 
drift sheets were formed bv ice moving from the northwest, 
whereas the Shelburne drift was oriented to the northeast. 
The relationship between the Burlington and Shelburne drift 
sheets in central Vermont as visualized by Stewart and Mac- 
Clintock (1969) is shown in figure 1. One of the purposes of 



298 



— I — : 

72* 30 



^■^2^ \\ Mon+pelier 



MONTPELIER QUAD 
BARRE QUAD 



PLAINFIELD QUAD 
EAST BARRE QUAD 




Barre 
J Granite 



DIRECTIONAL FEATURES 



Glacial striations, striations with 
range of directions, 



*\ Crag-ond-tail 



Till fabric (number of pebbles 
measured in parentheses) 



Figure 2. Glacial striations, till fabrics, and crag-and- 
tail feature in study area. Solid triangles represent field 
trip stops. Dashed line represents border of Burlington 
drift (compare with fig. 1). Directional features measured 
by F.D. Larsen , J.M. Ayres , D.A. Howard, J.G. Kvelums, S.A. 
Lawler, D.W. MacCormack , R.P. Magnifico, V.R. Sosnowski, 
and Squier. 



^yy 



this trip is to inspect, in the field, the validity of the 
relationship between the Burlington and Shelburne drift sheets. 

Acknowledgements 

This work, which is still in the reconnaissance stage, 
was originally developed as a doctoral problem but lack of 
funds prevented its pursuit for that purpose. The original 
impetus for this study arose from Douglas Selden, Norwich 
Univ. , '65, who wrote a paper on the history of the Dog 
River valley. Selden discovered four major terrace levels 
that can be related to a sequence of proglacial lakes that 
formed during deglaciation . Several students at Norwich Univ. 
have contributed to this study through projects in glacial 
geology. Eugene Rhodes, Univ. of Massachusetts, donated his 
services as a field assistant for three weeks during the 
summer of 1967. Dr. Joseph H. Hartshorn, Univ. of Massachusetts, 
and Dr. Barrie C. McDonald, Geological Survey of Canada, have 
contributed ideas to this study. 

Advance of Ice 

During the last major advance of Wisconsin ice in central 
Vermont , movement was to the south and southeast across rugged 
terrain with relief on the order of 1000 to 2000 feet. In 
the area shown as Shelburne drift (fig. 1), mapping of striations , 
till fabrics, crag-and-tail features, and an indicator fan de- 
rived from the Barre pluton, suggests ice movement to the 
south and southeast and not to the southwest as postulated 
by Stewart and MacClintock (1964, 1959). Striations and till 
fabrics mapped by glacial geology students at Norwich Univ. 
are shown in figure 2 (compare with fig. 1). 

Indicator Fan : An indicator fan based on pebbles derived 
from the Barre pluton was mapped during the summer of 1967. 
The first 100 pebbles encountered at each of 57 till localities 
were collected, washed, and, if necessary for identification, 
cracked open. The bulk of the pebbles were of metamorphic prov- 
enance comprising slates, phyllites, quartzites , and schists 
from the Waits River, Gile Mountain, Missisquoi, Stowe and 
Northfield Formations. However, 3 to 55 percent of the pebbles 
were of Barre-type granite, that is, light to medium gray granite 
with fine to medium texture. The percentage of granitic pebbles 
was plotted on a map and contoured with "isopers" (lines of 
equal percent) (fig. 3). The apparent long axis of the indica- 
tor fan trends toward S 15° E. Granitic pebbles which lie north 
and west of the 10 percent isoper represent a background count, 
and are assumed to have been derived from granitic bodies at 
Adamant, Woodbury, Hardwick, and unknown localities. Granitic 
pebbles derived from the Knox Mountain pluton, located to the 
east and northeast of the Barre pluton, are undoubtedly mixed 
with those from the Barre pluton. Since the color and the tex- 



300 



72° 30 



LEGEND 



Site o-f pebble count 
•'^ and percent otgronitic 
pebbles 



10 



J 



Isoper (line ot equal 
percent) 



-44»00' 



A Barre Quad 

B East Barre Quad 

C Randolph Quod 

D Strottord Quod 




44°00 



2 miles 



72° 30 
I 



Figure 3. Indicator fan of pebbles from the Barre Granite 
(location of bedrock exposures from Murthy , 1957). 



i 



301 



ture of granite from the two plutons is similar in appearance 
it is not possible to readily distinguish the source of peb- 
ble-size clasts. The Barre Granite is relatively homogeneous 
in texture and has few distinguishing features. In contrast, 
the Knox Mountain Granite is cut by numerous pegmatite dikes, 
and often contains garnets of pinhead size. Therefore, it is 
possible to identify the source of some of the larger erratics 
on the basis of features other than color and texture. 

Boulder Train : East-west traverses in the area south of 
the Barre plufon indicate that there is a sharp line separating 
terrain with few granitic erratics on the west from terrain with 
numerous granitic erratics on the east. This line trends due 
south from the westernmost bedrock exposures of Barre Granite 
and roughly parallels the 10 percent isoper on the indicator 
fan. Although detailed mapping of granitic erratics is in- 
complete , the concentration of erratics is high in a north- 
south zone 0.5 to 2 miles wide and 10 miles long, and appears 
to decrease eastward over the next 3 to 4 miles, at which 
point erratics derived from the Knox Mountain pluton increase 
in numbers. A line representing the westernmost occurrence 
of granitic erratics with pegmatite dikes and/or pinhead gar- 
nets extends S 5° F from the westernmost exposure of Knox 
Mountain Granite. 

It appears that , extending due south from the Barre plu- 
ton, there is a boulder train within a larger indicator fan 
which is defined by pebble counts, and which trends S 15° E. 
If this is true, I suggest that the first glacial erosion of 
the Barre pluton was by an ice sheet moving to the southeast. 
At this time, only pebbles and small erratics were being erod- 
ed. At a later time, when erosion had cut deeper into the plu- 
ton to pluck out large erratics , movement of the ice was due 
south. This suggestion of shift of movement from southeast to 
south has a precedent in diagrams of other Vermont indicator 
fans. As shown by Flint (1971, p. 178), indicator fans of 
Craftsbury Granite and a quartzite at Burlington have a long 
boundary stretching southward from a source area and a short 
boundary on the southeast side. This pattern may best be ex- 
plained by a gradual shift in direction of movement from 
southeastward, as the ice sheet built up, to southward when 
the ice sheet reached a maximum thickness. Whatever the cause 
of this apparent or real discrepancy between the axes of the 
indicator fan and the boulder train, there is no evidence of 
major ice movement to the southwest in the vicinity of the 
Barre pluton as suggested by Stewart and MacClintock (19 69). 

Deglaciation 

Downwasting of ice in central Vermont first witnessed 
the emergence of the Green Mountains as linear rows of nuna- 
taks. Evidence of vigorous fluvial erosion during the early 
stages of deglaciation comes from a large pothole on Burnt 



302 




HIGH-LEVEL LAKES OF 
NORTH-CENTRAL VERMONT 
STAGE I 

j I BURLINGTON ICE 



LAKE WATER WITH 
ELEVATION OF PRES- 
ENT SHORE FEATURE J 

PROBABLE OUTLET 



ICALI IM MILI* 



HKW- LEVEL LAKES OF 
NORTH-CENTRAL VERMONT 
STAGE S. 

BURLINGTON ICE 




LAKE WATER WITH 
ELE\«TION OF PRES- 
ENT SHORE FEATURES 

PROBAeLE OUTLET 



KALI W MILCt 



H 




HIGH-LEVEL LAKES OF 
NORTH-CENTRAL VERMONT 
STAGE m. 

|~1 BURLINGTON ICE 

I LAKE WATER WITH 
ELEVATION OF PRES- 
- ENT SHORE FEATURES 
«/ PR0BA8LE OUTLET 



KALI IN MILCt 




Figure U . High-level lakes of central Vermont according to 
Stewart and MacClintock (1969, figs 18-22, published by per- 
mission of Dr. Charles G. Doll, Vermont State Geologist). 
Only the lower half of the original figures were reproduced. 



303 



Rock Mountain situated on the crest of the Green Mountains 
16 miles due west of Montpelier. The pothole, described by 
Doll (1936), is at an approximate elevation of 2820 feet. 
Continued downwasting resulted in long coalescent masses 
of stagnant ice filling the valleys of the Winooski River 
and its tributaries. Drainage in the main Winooski valley 
was blocked, therefore the surfaces of the ice masses prob- 
ably rose to the northwest with a low gradient. 

A sequence of early proglacial lakes that formed in the 
central Vermont area, according to Stewart and MacClintock 
(1969), is shown in figure H. The sequence of diagrams clearly 
implies that thresholds at Roxbury and south of Williamstown 
are erosional, having been lowered 240 feet and 110 feet re- 
spectively. It is the contention of this report that neither 
threshold was affected appreciably by runoff from glacial 
lakes (possibly 5 to 20 feet of till were removed from each 
threshold), because ice-contact features immediately north 
of each threshold are constructional in origin. 

Proglacial lakes developed where north-flowing tribu- 
taries, such as the Mad River, the Dog River, and the Stevens 
Branch, were dammed on the north by stagnant ice (further 
discussion of the Mad River is not included in this report). 
These lakes drained southward over bedrock thresholds into 
the drainage system of the Connecticut River (fig. 5). 

In the Dog River valley there are four groups of ter- 
race levels, (1) 1010 to 1020 feet, (2) 910 to 920 feet, 
(3) 740 to 760 feet, and (4) 640-680 feet, which punctuate 
the history of deglaciation into four stages. The first three 
groups of terraces consist mostly of constructional surfaces 
(deltas, kame deltas or kame terraces), and were controlled 
by proglacial lakes , the sequence of which depended upon the 
position of an ice margin during deglaciation. The fourth 
group of terraces is believed to be mostly erosional, as are 
terraces whose elevations do not fall within one of the four 
major groups 

Stage I 

Glacial Lake Roxbury : The highest terraces are associ- 
ated with a lake which was controlled by a threshold at 1010 
feet elevation at Roxbury, and which drained southward by way 
of the Third Branch of the White River (fig. 5). This lake 
was first noted, but not named, by Merwin (190 8, p. 124). It 
is named here glacial Lake Roxbury. The major evidence for a 
lake at 1010 feet is a large ice-contact delta (Stop 9) situ- 
ated 1.3 miles north-northeast of Roxbury. Foreset bedding, 
ripple-drift cross-lamination, and dune bedding, each indicating 
a southward transport direction, are exposed in a sand and gravel 
pit, now used for a sanitary landfill. The contact between 
topset and foreset bedding at 1012i feet elevation is exposed 
in the southwest corner of the pit. The delta, 0.8 of a mile 
long, is a constructional feature since its surface is pock- 



304 



\ ^\ \ 


•/ 


/\\: 




\^\^ o 


/ 


K 1^ 


/^^^"^ 


I X- \y 




V<v 


^\ I 








] y-sX^ 


\ ^ y 




Tx S C 


7 / ^ 


l^^jiiwi^ 




) •'r~ 


y/LAKE 


^2r^ / 




f\ 1 r ^ 


5y WILLIAMSTOWN 




^ 


^ Ca, 


1 


c^-~--\ /fX^i ^ 


1-/1B10 

r 


LAKE 


1 •*!■*' 


LAKE A^ 




ROXBURY 


1 1111'' 


"1 M ii_c: 3 


GRANVILLE j) 






1 


r" 






STAGE I 



Figure 5. Stage I, Lakes Williamstown , Roxbury , and Granville. 




Figure 6. Stage II, Lake Winooski, 



305 



marked with kettles on the north, and it was fed by a subglacial 
stream as indicated by an esker which extends 1.2 miles east- 
southeast from the head of the delta. 

Retreat of the ice margin from the ice-contact deltas was 
accompanied by the northeastward expansion of Lake Roxbury. 
Just how far north the 1010-foot lake extended is not known, 
however features in ice-contact gravels 1.0 miles north of 
Northfield indicate a transport direction to the south. Also 
ripple-drift cross-lamination in lacustrine sands at Riverton 
dips to the south. Three small 1000-foot terraces (kame deltas) 
on the east side of the Dog River valley at Northfield may or 
may not have been deposited in Lake Roxbury. The location of 
the three features in relation to the post office at Northfield 
is as follows: (1) 0.3 of a mile east, (2) 0.75 of a mile south, 
and (3) 1.4 miles south. Good exposures are lacking in the 
three deltas, therefore direction of transport and topset- 
foreset relationships are unknown. 

Glacial Lake Williamstown : Shortly after the formation 
of Lake Roxbury, a proglacial lake developed in the valley of 
the Stevens Branch. The lake, named Lake Williamstown by 
Merwin (1908, pi. 21B) , drained over a threshold at 915 feet 
elevation, 2.3 miles south-southwest of Williamstown (fig. 5). 
Southward dipping foreset beds in a kame terrace, 0.2 5 of a 
mile east of Williamstown, clearly indicate the former presence 
of a standing body of water. Drainage of the lake was to the 
south through Williamstown Gulf by way of the Second Branch 
of the White River. That stagnant masses of ice choked the 
Stevens Branch valley during deglaciation is shown by the 
plentiful occurrence of eskers and kame terraces for at least 
5 miles north of the threshold. The presence of unfilled 
kettles in the kame terraces testifies to the constructional 
origin of the land forms. 

Continued downwasting and retreat of the ice margins 
bordering Lakes Roxbury and Williamstown finally resulted in 
the lowering of Lake Roxbury by 9 5 feet to the level of Lake 
Williamstown. This occurred when ice withdrew below the 1000 
foot contour (approximate) on the ridge separating the valleys 
of the Dog River and the Stevens Branch. The locality is on 
the Barre quadrangle, 2.5 miles north of Berlin. 

Stage II 

Glacial Lake Winooski : The second group of terraces in 
the Dog River valley, at 910 to 920 feet, lies 90 to 100 feet 
below the former level of Lake Roxbury. The features are best 
developed in the vicinity of Harlow Bridge School, 2.25 miles 
south-southwest of Northfield. A large delta, with surface 
elevations greater than 920 feet, is situated 0.6 of a mile 
west of Harlow Bridge School. Well developed terraces lie 
above the 900 foot contour northwest, southwest, and south of 
Harlow Bridge School. 



306 



"^^^^^ 


if 




Z' 


J . 


y ^ 


/ 


^ «=^/^Gillett Pond 

1 

V 7^ 


t4 




i 


1 \ 




/^ 


1 


"^ 






•y ^'^iC*—*'—*— 


V 




i- 


x^ (^ 


v.A<^ 




^L 






LAKE MANSFIELD 


^. 


/ 




/ 






STAGE nr 




^ 


• 


Mii_CS , 











Figure 7. Stage III, Lake Mansfield. This map is intended 
as a first approximation only, and was obtained by tracing 
the 700-foot contour on the Lake Champlain sheet of the 
AMS 1:250,000 series. 



■I 



307 



Foreset beds of fine sand and silt occur in a small pit 
0.1 of a mile southeast of the Harlow Bridge School. Here, 
ripple-drift cross-lamination at 850 feet elevation indicates 
that during deposition transport of sediment was to the north. 
An area of hummocky ground with summits at 900 feet elevation 
extends for 1.2 miles south of Norwich University. The area 
has a core of bedrock and ice-contact stratified drift, the 
latter displaying features indicating a southward transport 
direction. Covering the bedrock and drift core is a mantle 
of sand and silt. The area probably was underlain by masses 
of buried ice which were covered by deltaic and lacustrine 
sediments deposited by Sunny Brook which enters the Dog River 
1.8 miles south-southwest of Northfield. Melting of the ice 
blocks resulted in the collapse of the 900 foot delta surface. 
Similar collapsed topography occurs in the vicinity of the 
former Northfield dump, 1.0 mile north of Northfield. 

The development of terraces and deltaic surfaces at 910 
feet elevation requires the presence of a lake at that approx- 
imate elevation. This lake is glacial Lake Winooski (fig. 6) , 
which was formed by the coalescence of Lake Roxbury and Lake 
Williamstown. The development of a major new lake by the co- 
alescence of two previously named lakes is assumed here to 
require a different name for the single lake thus formed. 
Merwin (1908, p. 138) used the term "First Lake Winooski" to 
describe a lake which was blocked by an ice margin between 
Middlesex and Plainfield and lower portions of the valleys of 
the Dog River and the Stevens Branch. However, First Lake 
Winooski was "represented by an altitude of 745 feet at Plain- 
field" (Merwin, 1908). It is not clear where the outlet of 
the lake was situated, however, Merwin must have assumed that 
it was over ice toward the west-northwest. In the stage 
following First Lake Winooski, Merwin shows Lake Mansfield 
with an outlet along the ice margin west of the Green Mountains. 
Because Lake Mansfield may be a valid term, and because the 
outlet of First Lake Winooski is questionable, the term Lake 
Winooski is used to describe the temporary proglacial lake 
which drained south through Williamstown Gap after the coalescence 
of Lake Roxbury and Lake Williamstown. 

Stage III 

Lake Mansfield : In the Dog River valley there is a wide 
range of constructional and erosional terraces below 900 feet 
elevation. However, the next most consistent group of terraces 
occurs between 740 and 76 feet. Union Brook, Cox Brook, and 
Chase Brook, southeast-flowing tributaries of the Dog River, 
have each built small deltas into a lake at this level at North- 
field, Northfield Falls, and just north of Riverton , respective- 
ly. Delta surfaces are common between 720 and 760 feet ele- 
vation throughout the upper Winooski drainage area suggesting 
that they all share a common origin in a single lake. Since 
the lowest divide between the Champlain valley and the Connec- 



308 



Mon+pelier 



72* 30' 



MONTPELIER QUAD 
BARRE QUAD 



-44* IS 



US 2 



PLAINFIELO QUAD. 



EAST BARRE QUAD. 



-44»I9 - 



N 



)Riverton 



iRoxbury 
'8 



/North-field 




Eiit e 


L Falls 


/ 


f " 
North-field' ) 


// 




1 


^^^^cly^^-1 


^E.it 5 f^^-' 


Northfield 







Barre 



'South 
Barre 



v2/East 
Barre 



Williamstown 

7 



4 MILES 

-J 



/^Cutter 
Pond 

^V; Williamstown 
S'^- Gulf 



72* 30 

I 



Figure 8. Route for Field Trip G-1. 
stops. 



Solid triangles denote 



ill 



309 



ticut valley is the 915-foot threshold south of Williamstown , 
the outlet for a lower lake must lie west of the Green Mountains. 

Merwin (190 8) suggested the name Lake Mansfield (fig. 7) 
for a lake in the Winooski valley which had an outlet along an 
ice margin in the vicinity of Huntington. A possible outlet 
for Lake Mansfield lies just northeast of Gillett Pond, 2.9 
miles N 31° E of Huntington. However, the Gillett Pond thresh- 
old lies at an elevation of 740 feet which is the same eleva- 
tion as the terraces in the Dog River valley. Studies in south- 
ern Quebec (McDonald, 1967), the Champlain valley (Chapman, 
1937), and the lower Connecticut valley (Jahns E Willard, 19H2) 
indicate that regional tilting of the surface of New England 
has occurred since removal of the weight of the last continental 
ice sheet. The amount of tilt that has occurred since late- 
glacial time is on the order of 4 feet per mile. Since Gillett 
Pond lies 20 miles northwest of the Dog River valley (measured 
perpendicular to isobases), the outlet should be approximately 
80 feet higher than the 7i+0-foot terraces in the Dog River 
valley. Since the Gillett Pond threshold lies at 740 feet 
(approximate), either (1) the outlet has been lowered 80 feet 
by erosion, or (2) the 740-foot terraces in the Dog River valley 
were deposited in higher lakes controlled by temporary thresh- 
olds related to blocks of stagnant ice, or (3) some combina- 
tion of these two has occurred. 

Stage IV 

Well-formed terraces occur at elevations of 640 to 6 80 
feet in the Dog River valley. Since these features are erosional 
and slope down valley, they can probably be related to one of 
two possible situations. The first is a glacial lake with a 
660-foot threshold through Hollow Brook, 2.0 miles S 36<» W of 
Huntington. Diversion of drainage over the Hollow Brook thresh- 
old would require blockage of the lower Winooski valley in 
the vicinity of Richmond following retreat of ice from the 
Gillett Pond outlet. If such a blockage did not control Stage 
IV terraces in the Dog River valley, then possibly they are 
graded to a level of Glacial Lake Vermont. Since close field 
inspection has not been made of possible thresholds west of 
the Green Mountains, the above discussion of Stages III and 
IV must be considered conjectural at this time. 

Road Log 

Mileage 

START: MONTPELIER QUADRANGLE 

0.0 Begin mileage count and turn right at intersection of 
Bailey Avenue (U.S. 2) and exit from Montpelier High 
School parking lot. The parking lot is on the flood 
plain of the Winooski River and was under 6 feet of 
water during the flood of 1927. 



310 



0.1 Cross railroad tracks and turn left on Memorial Drive, 

proceed east on U.S. 2 along the south bank of the 

Winooski River. 

Continue straight ahead at traffic light , crossing Rt . 12. 
0.6 Striated exposure of Waits River Formation on the right 

(see fig. 2) 

1.05 BARRE QUADRANGLE 

2.2 Turn right (south) and follow U.S. 30 2 to East Barre . 
Route leaves the Winooski River and follows the valley 
of the Stevens Branch. 

3.0 Varved clay on the right represents bottom sediments of 
glacial Lake Winooski, or glacial Lake Mansfield. In 
the spring of 1960, this locality was the site of an 
earthflow which covered 2 of the 3 lanes of the Barre- 
Montpelier Road. 

3.3 Material and Soils Laboratory of the Vermont State High- 
way Department on the left. 

6.6 Rt. 14 enters from the left, continue straight ahead. 

7.1 Bear right, then turn left around municipal park in the 
center of Barre, follow U.S. 302. Road ascends to 720 
foot terrace (delta?). 

7.2 EAST BARRE QUADRANGLE 

7.5 Exposure behind gas station on the left has lacustrine 
sand which contains angular ice-rafted pebbles , and which 
is overlain by till. Road enters the valley of the Stevens 
Branch. 

8.6 View ahead of Cobble Hill. 

9.3 View of Jail Branch section on left. 

10.1+ Turn left at junction of U.S. 302 and Rt . 110 

10.5 Bear left at Y. 

10.7 Bear left as 2 roads branch to the right. 

11.3 Park on right at gravel pit in ice-contact stratified drift. 

Cross road and walk southwestward across field to top of 

bank. 

STOP 1 . Jail Branch Section. From the base up, the section consists 
essentially of fine-grained lacustrine sediments (silt and clay) 
which grade upward into lacustrine fine sand and silt which, in 
turn, is overlain by gravel and sands of probable outwash origin, 
and finally till with large erratics of Barre Granite. This sequence 
is believed to be the result of blockage of the Jail Branch by ad- 
vancing ice which finally encroached upon and overran a lacustrine 
sequence. The sequence is preserved because it is situated in the 
erosional shadow of Cobble Hill. 

Retrace route to U.S. 302. 

12.2 Continue straight ahead (south) crossing U.S. 302 and the 
Jail Branch. 

12.3 Turn left at Y, follow Rt. 110. 

12. H Bear right, leaving Rt . 110, on road to Upper Graniteville. 
13.1 Turn right (west) on dirt road which passes several large 
grout sites. 

13.4 Park on right side of road. 



J. 



311 



STOP 2 . A brief photographic stop at abandoned quarry to view 
sheeting in the Barre granite. 

13.9 View of Jail Branch section and Cobble Hill to the right. 

14. 2 Stop sign, turn left (south). 
15.4 Turn left (southeast). 

15.6 Rock of Ages Tourist Center on the right. 

15.7 Park on right side of road adjacent to Rock of Ages quarry. 

STOP 3 . Gray till overlies Barre granite and basic dike. The 
till contains numerous striated clasts of calcareous quartzite 
derived from the Waits River Formation. Striae on granite trend 
due south. 

Proceed straight ahead , roads enter from the right , then 
from the left. 

16.3 Continue straight (south) at crossroad. 

17.4 Park on right side of road, walk to top of Mount Pleasant, 
elevation 2063 ' . 

STOP 4 . Barre Granite Indicator Fan and Boulder Train. Mount Pleasant 
IS underlain by gray phyllite and slate of the Gile Mountain Formation. 
However, the top is covered with numerous granite erratics of medium- 
grained, gray granite. The nearest outcrop of Barre granite lies 
0.6 miles to the north and 500 feet lower than the summit of Mt . 
Pleasant . 

Return to cars, proceed straight ahead. 

17.5 Make U-turn in driveway of summer home. 

18.6 Turn left (west) at crossroad. 

19.1 Continue straight ahead with caution, road enters from the 

right. 
19.9 Turn left (south) to Baptist Street. 

20.4 Bear right as route enters Baptist Street. 
2 0.9 BARRE QUADRANGLE 

21.1 View to the west of Paine Mountain and the Green Mountains. 
23.1 Jackson Corner, continue straight ahead. 
23.3 Park on right side of road. 

STOP 5 . White Rock. A mass of vein quartz measuring 115 x 45 x 15 
feet is the crag of a large-scale crag-and-tail feature. The axis 
of the tail trends due south supporting the contention that the 
last important ice movement in this area was due south. Numerous 
blocks of vein quartz may be found located in a stone wall 375 feet 
south of White Rock. 

Return to cars , reverse direction either by backing up or 
by proceeding south to farm at end of road. 

23.5 Turn left at Jackson Corner, road descends into the valley 
of the Stevens Branch. 

25.5 Turn left (south) on Rt . 14, gravel pit on west side of 

valley is in ice-contact stratified drift graded southward 
to the threshold of glacial Lake Williamstown. 

26.3 Esker on the left. 



312 



26.7 Cutter Pond, elevation 912 feet on the left. 

26.8 Threshold of glacial Lake Williamstown , approximate 
elevation 915 feet. Road descends into Willicimstown Gulf, 
a V-shaped valley deepened by the outlet from glacial 
Lake Williamstown. 

2 8.3 Turn to the right into parking lot of restaurant in 

Williamstown Gulf, make U-turn with caution and rejoin 
Rt. 14 north. 

28.8 Turn left on dirt road. 

30.0 Stop at Staples Pond, elevation 890 feet. 

STOP 6 . Outlet of Lake Williamstown and Lake Winooski. During 
deglaciation , when drainage to the north was blocked by stagnant 
ice. Lake Williamstown formed north of Cutter Pond and drained 
southward through this area to Williamstown Gulf. 

30.9 Turn left (north) on Rt . 14, proceed to Williamstown. 

3 3.1 Turn right into yard of Burrell Roofing Compamy 

STOP 7 . Ice-contact features at Williamstown. The sheet metal 
shop is located at the south end of a discontinuous esker which 
shows on the Barre quadrangle as a single closed contour at 880 
feet elevation. Foreset beds and ripple-drift cross-lamination 
dip to the south. Collapsed and faulted beds are common behind 
the sheet metal shop and in a small pit 100 feet to the north. 
The view to the northeast is of a partially excavated kame delta 
with foreset beds which dip to the south. In view of the wide- 
spread occurrence of ice-contact features deposited in relation 
to the 915-foot threshold of Lake Williamstown, the topography 
is considered to be constructional. 

Proceed north on Rt. 14. 

33.4 Turn left (west) leaving Rt. 14 at center of Williamstown. 
34.6 Bear right at Y. 

35.6 View left (east) into the valley of the Stevens Branch. 

36.1 Drainage divide, elev. 1715 feet, enter drainage basin of 
Dog River. 

37.5 Pass under 1-89, several sharp curves ahead. 

40.2 Stop sign, turn right (northeast) on Rt . 12 in the village 
of South Northfield (!) situated in the valley of Sunny 
Brook. 

40.5 Turn left (west) on dirt road which leaves Rt . 12 and 

follows Sunny Brook. 
41.1 Stop sign, turn left (south), follow Rt . 12A and Dog 

River valley to Roxbury. 

46.3 Turn right to railroad depot at Roxbury. 

STOP 8. The depot at Roxbury is situated on the drainage divide of 
a small through valley. The Dog River descends from the slope on 
the west and turns to the north, whereas the Third Branch of the 
White River enters the valley from the east and turns to the south. 
The drainage divide, at an elevation of 1010 feet, is the former 
threshold of glacial Lake Roxbury. 

Proceed north on Rt. 12A. 



313 



46.8 Camp Teela-Wooket on the right. 

47. Rt. 12 passes through terrace graded southward to the 
Roxbury threshold. 

4 7.2 Terrace on the right. 

47.6 Rt. 12 rises on the front of ice-contact delta. 

47.8 Turn right into gravel pit being used as sanitary landfill 
dump. 

STOP 9 . Ice contact delta. Foreset bedding, dune bedding, ripple- 
drift cross-lamination, and imbricate structure indicate southward 
transport of sediment during construction of the delta. Maximum 
height of foreset beds overlain by topset beds is on the order of 
1012 to 1015 feet indicating deposition in a lake whose elevation 
was controlled by the Roxbury threshold. Collapsed bedding, kettles, 
and an esker, which extends 1.2 miles down the Dog River valley, 
give evidence of an ice-contact origin for the delta. Headward 
erosion increased the length of the gully at the southeast corner 
of the pit by 50 feet between October, 1970, and October 1971. 

Return to Rt . 12A, proceed north. 

48.7 Railroad overpass and bridge over Dog River. 

50.1 Park on right side of Rt. 12A, cross wooden bridge over 
Dog River, enter pit. 

STOP 10 . Neun Pit (tentative stop). Sediments in the lower portion 
of pit are gravel, sand, and silt which display foreset beds (bar 
slip faces?) and dune bedding which indicate transport of sediment 
to the west, or up the Dog River valley. Transport direction in 
the overlying stream gravel was to the east as shown by imbrica- 
tion of pebbles. The lower sediments are assumed to be ice-contact 
deposits formed by a subglacial stream flowing into Lake Roxbury. 
The upper stream gravels were deposited by the Dog River which, at 
the time of deposition, was graded to Lake Mansfield or to later 
stage deposits. 

Proceed north on Rt. 12A. 
50.5 Cross Dog River in middle of Northfield Country Club. Sky- 
line to the left (north) is the surface of a 920-foot delta 
formed in Lake Winooski. Note terraces on the golf course 
at the right. 

51.3 Pass under Harlow Bridge, scene of famous 1867 railroad 
disaster in which several railroad cars were accidently 
pushed from half-completed bridge. 

51.4 Harlow Bridge School on left. Pit to the right on Bull 
Run Road has fine sand in bottomset beds , or low-dipping 
foreset beds, deposited in Lake Winooski. Ripple-drift 
cross-lamination at 850 feet elevation dips to the north. 

51.9 Bridge over Sunny Brook. For the next 0.8 of a mile hum- 
mocky ground lies on the right. 

52.7 Stop sign, turn left (north) on Rt . 12. 

5 2.8 Turn left at small park. 

52.9 Park on right for brief rest stop at Norwich University. 

Proceed north on Rt . 12 through the village of Northfield. 



31^ 



53.7 Downtown Northfield (Depot Square). 
5 3.8 Bridge over Dog River. 

5 3.9 Traffic light, terrace to left is surface of 740-foot 
delta built into Lake Mansfield. 

54.6 Bridge over Dog River. 

54.7 Turn right (east) on dirt road just past Catholic Ceme- 
tery. Road rises to 700-foot terrace. 

54.9 Park on right, walk south along 700-foot terrace to 
former site of Northfield town dump. 

STOP 11 . Collapsed lacustrine sediments are exposed in a face 
200 feet long and 15 to 30 feet high. Thick layers of fine 
sand and silt at the base grade upward into thin layers of varved 
silt and clay. Ripple-drift cross-lamination in the sand layers 
dips to the north. Angular, ice-rafted clasts of fine-grained 
chlorite schist and greenstone occur in a layer about 10 feet 
above the base of the section. Striations occur on a green- 
stone clast which measures 2' x 2' x 1'. The occurrence of 
fine-grained lake-bottom sediments at elevations up to 760 feet 
suggests deposition in glacial Lake Winooski (Stage II). The 
presence of angular clasts testifies to the presence of ice- 
bergs in the lake » and large scale collapse, as shown by dipping 
and faulted beds , indicates lacustrine sedimentation over buried 
ice. Large folds formed by collapse were once exposed in a 
lower portion of the pit now covered by the dump. Gravel over- 
lies collapsed and truncated layers of fine sand at the right. 

55.1 Turn right (north) on Rt. 12. 

55.2 In the pit at the right ice-contact gravels with features 
indicating southward transport capped by stream gravels 
with imbrication suggesting northward transport. The 
stream gravels are the same deposits that underlie the 
700-foot terrace at STOP 11. 

55.8 Turn left (west) at IGA Store in Northfield Falls, con- 
tinue through covered bridge over Dog River and over 
railroad tracks. 

55.9 Turn right (north) just beyond railroad tracks. 

56.3 Terrace at 660 feet elevation underlies red barn on the 
right. Road ascends bedrock spur. 

56.5 Brief photographic stop on the right, time and weather 
permitting. 

56.7 Road descends to 6 80-foot terrace with view of three 

erosional terraces below. Exposure to the right is in 
ice-contact gravels with directional features oriented 
to the south. 

57.1 Road drops to 660-foot terrace. 

5 7.3 Road drops to brook and reascends to 660-foot terrace. 

5 7.9 Entrance to gravel pits on the right. 

5 8.1 Turn right into driveway which circles West Berlin (River- 
ton) School and park. 



315 



STOP 12 . Riverton Water Gap. During Stage III a TUO-foot delta 
was apparently deposited across the preglacial course of the Dog 
River, 0.6 of a mile due north of the West Berlin School. Low- 
ering of Lake Mansfield, caused by a change in outlets west of 
the Green Mountains, nermitted the superposition of the post- 
glacial Dog River across a bedrock spur 0.7 of a mile north- 
northeast of West Berlin School. 

Proceed north on dirt road. 
58.3 Stop sign, bear left (north) on Rt . 12. 
58.9 Riverton water gap. Bedrock exposed is fine-grained 

chlorite schist of the Cram Hill Member of the Missis- 

quoi Formation. 
60.0 Slump terracettes on the left. 
6 0.5 Turn left (northwest) on road to pit. 

STOP 13 . Herring Pit (tentative stop). Ice-contact stratified 
drift with features indicating southward transport occur at 
elevations up to 680 feet. 

Proceed north on Rt . 12. 

61.3 Abandoned potholes occur in a railroad cut behind a 
trailer on the left. They appear to have been cut by 
the Dog River before the last glacial advance because 
they probably were filled with lacustrine sediment that 
occurs adjacent to the railroad cut. 

61.5 Road follows flood plain of the Dog River for 1.1 miles. 

62.5 Turn left (northwest) on dirt road. 

62.6 Turn left (southwest) to exposure. 

STOP 14 . Collapsed mass of ice-contact stratified drift. The 
exposure is all that remains of a small hill 0.4 of a mile south- 
east of the point where the Dog River leaves the Barre quadrangle, 
The original feature was 500 feet long and over 50 feet high. 
All types of glacial sediments, including till, have been seen 
in the hill as it was being reduced by man. Highly distorted 
clay-silt varves presently overlie boulder gravel on a contact 
that strikes N 15° E and dips 40° northwest. Is the feature 
a constructional or an erosional land form? 

Return to Rt . 12, proceed north. 
6 3.1 Enter Montpelier 
6 3.4 MONTPELIER QUADRANGLE 
64.0 Traffic light, turn left (west) on U.S. 2. 

64.4 Turn right over railroad tracks. 

64.5 Turn left into parking lot of Montpelier High School. 

REFERENCES 

Chapman, D.H., 1937, Late-glacial and post-glacial history of the 
Champlain Valley: Amer. J. Sci., v. 34 (5th ser. ) , p. 89-124. 

Doll, C.G., 1936, Glacial pothole on the ridge of the Green Moun- 
tains near Fayston, Vermont: Vermont State Geologist, 2 0th 
Report, p. 145-51. 



316 



Flint, R. F. , 1956, New radiocarbon dates and late-Pleistocene 
stratigraphy: Amer. J. Sci., v. 254, p. 265-287. 

, 1971, Glacial and Quaternary geology: John Wiley and 

Sons, New York, 892 p. 
Gadd, N.R., 1964, Moraines in the Appalachian region of Quebec; 
Bull. G eol. Soc. Amer . , vol. 75, p. 1249-1254. 

and Willard, M.E, , 1942, Late Pleistocene and recent 
in the Connecticut Valley, Massachusetts: Amer. J. 
240, p. 161-191, 265-287. 

Outline of Pleistocene geology of Martha's Vine- 
U.S. Geol. Surv. Prof. Pap. 501-C, 



Jahns 



Kaye, 



, R. H. , 

deposits 

Sci. , V. 

C. A., 1964, 

yard, Massachusetts 

p. 134-139. 
McDonald, B.C., 1967, Pleistocene events and chronology in the 

Appalachian region of southeastern Quebec, Canada: Unpub- 
lished Ph.D. Dissertation, Yale University, 161 p. 
Merwin, H. E. , 1908, Some late Wisconsin and post-Wisconsin shore- 
lines of north-western Vermont 

6th Report, p. 113-38. 
Murthy, V. R. , 1957, Bedrock geology of the East Barre area 

Geol. Survey Dull. 10, 121 p. 
Naylor, R. S., 1971, Acadian orogeny 

Science, v. 172, p. 558-559. 
Schafer, J. P., 1967, Retreat of the 

[abs.]: Geol. Soc. America Program 1967, 

Northeastern Section, p. 55. 
Stewart, D. P., 1961, The glacial geology of Vermont: Vt. Geol. 

Survey, Bull. 19, 124 p. 
Stewart, D. P., and MacClintock, Paul, 1964, The Wisconsin 

Stratigraphy of northern Vermont: Amer. J. Sci., v. 262, 

p. 1089-1097. 

, 1969, The surficial 

Geol. 



Vermont State Geologist, 

Vt. 

An abrupt and brief event: 

last ice sheet in New England 
Annual Meeting 



Vermont: Vt. 



geology and Pleistocene history 
Survey, Bull. 31, 251 p. 



of 



"We are unable to adopt these views; first, because all 
known glaciers are confined to valleys, though at their head 
they may be connected with extensive fields of ice, capping 
the summits of the mountains: secondly, because no known glacier 
is more than 50 or 60 miles wide (the great glacier called Hum- 
bolt, in Greenland, described by Dr. Kane, is of this width), 
whereas the ancient American glacier must have been at least 
2500 miles wide, and have spread over all the mountains as well 
as valleys, and often have been obliged to move up hill as well 
as over a level surface: thirdly, because in our country we have 
two and probably three prominent directions to our drift, and 
it is difficult to see how one glacier would have moved in so 
many directions, especially as the most usual course of the striae 
in New England does not follow a valley, but crosses over mountains 
obliquely. " 

. . . .Edward Hitchcock, 1861 

Geology of Vermont, v. 1, p. 91. 



^L 



317 



Trip G-2 



ICE MARGINS AND WATER LEVELS IN , NORTHWESTERN VERMONT 



by 



W. Philip Wagner 
University of Vermont 



PROGLACIAL LAKES IN THE LAMOILLE VALLEY, VERMONT 



by 

G. Gordon Connally 
State University of New York at Buffalo 



1 



319 



ICE MARGINS AND WATER LEVELS IN NORTHWESTERN VERMONT 



by 



W. Philip Wagner 
University of Vermont 



INTRODUCTION 



In what has become a classic reference for late Pleistocene 
drainage history in the Champlain Valley, Chapman (1937) delin- 
eated a series of lacustrine and marine water bodies associated 
with retreat of the Laurentide ice sheet. Successively lower lev- 
els of proglacial Lake Vermont extended progressively further 
northward, following the retreating ice margin. Finally, ice re- 
treat allowed the influx of marine waters forming the Champlain 
Sea (Harrow, 1961). Numerous investigators working in the Green 
"lountain uplands have recognized the existence of local lakes, 
'.vhicn were impounded between the highly irregular topograohy and 
the Laurentide ice margin, and which were partly contemporaneous 
••/ith Lake Vermont. The publications by Connally (1966) and Ste- 
\/arl: and MacClintock (1969, 19 70) are recent examples. 

This report summarizes research on Pleis;;ocene proglacial e- 
vents in the Champlain Valley and adjacent Green Mountain uplands. 
Numerous students at the University of Vermont provided assistance, 
including R. Switzer, C. A. Howard, Jr., W. R. Parrott, Jr., and 
3. P. Sargent. The use of data from dissertations by Johnson 
(1970) and Waite (1971) is gratefully acknowledged. G. G. Connal- 
ly, C. S. Denny, and B. C. McDonald reviewed early drafts of the 
manuscript. The work upon which this report is based was suonort- 
ed by funds provided by the United States Department of Interior 
as authorized under the Water Resources Research Act of 1964, 
Public Law 88-379. 



WATER PLANES 



General 



Raised strandlines in the northern part of the Champlain Val- 
ley are marked by abundant but widely scattered shoreline fea- 
tures consisting primarily of deltas and beaches, but also includ- 
ing outlet channels, wave-cut benches, and spits. The locations 
of these features are shown in Figures 1 and 2. A listing of fea- 
tures, with pertinent information is provided in the appendix. 
Figure 3 is a north-south profile, constructed by westerly projec- 
tion of features, with elevation control provided by contour lines 
from topographic maps. 

Delineation of water planes is difficult in this area due to 



32« 




Figure 1: Shoreline feature locations and 
strandlines of regional water bodies in Cham- 
plain Valley: S = Champlain Sea; Gr = Greens 
Corners; F = Fort Ann; C = Coveville(?) ; Q = Qu=tk- 
er Si;rings(?); M = Miscellaneous. 



i 



321 



Gillett 

Huntington 

Hollow Brook 

Jericho 

Jericho Centei 

Stowe — 

The Creek — , — « 



/'iBakersfield 



SCALE 



N 

i 



4 Ml 

♦ 

> « 







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\. / 



S2 



i9,^^Underhill 



Mt. 
Mansfield 



G4_--...- -V.^GS 



G2 
•.■•-. Hu 7: 







Figure 2: Shoreline feature locations and generalized strand- 
lines of upland water bodies in the Green Mountains: G = 
Gillett; S = Stowe; T = The Creek; Hu = Huntington; Ho = Hol- 
low Brook; J = Jericho; Jc = Jericho Center. 



322 



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323 



the large scatter of shoreline features. Tlie most obvious align- 
ment of features on Figure 3 approximates the marine limit (Cham- 
plain Sea) of Chapman (1937, Figure 16), which is different from 
the marine limit of this paper based on the highest occurrences 
of marine fossils (Figure 3; Appendix). The Fort Ann (Chapman, 
19 37) and Greens Corners water planes on Figure 3 are drawn paral- 
lel to the marine limit so as to coincide with both the largest 
number of features possible as well as the more prominent features. 
TVbove the Fort Ann level distinct regional water planes are not ap- 
parent. Tiie Coveville (Chapman, 1937) and Quaker Springs (Stewart, 
1961) planes are tentatively recognized, based on correlation with 
features identified by others (Connally, 1968 and 1970; Denny, 
1970, personal communication). Features above the Quaker Springs 
level represent local lakes in the Green Mountains. By consider- 
ing topography, distribution of shoreline features, drainage re- 
quirements, and assumed configurations of the Laurentide ice mar- 
gin, water planes for local lakes above the Quaker Springs level 
were drawn parallel to the regional, lowland water planes. 

The accuracy of Figure 3 is affected by a variety of sources 
of error. If combined, errors could result in some features being 
misplotted 40-50 feet too high or low on Figure 3. Comparison of 
Figure 3 with a similar profile from the New York side of the Cham- 
plain Valley by Denny (1970, personal communication) indicates very 
close agreement for the major regional strandlines common to both 
profiles (marine limit; Fort Ann; Coveville [?]) . Water planes for 
local , upland lakes are considered tentative in view of data limi- 
tations. 

Existing terminology has been considered in naming the various 
levels. Although the original or prevailing concepts associated 
with individual regional water planes differ somewhat from the 
views presented here, these differences do not warrant introducing 
new names. Thus, except for Lake Greens Corners, which is a newly 
defined level, the lake names used by Chapman (19 37) and Stewart 
(1961) are retained for regional lake features in the study area. 
On the basis of work at the southern end of the Champlain basin, 
south of the study area, Connally (1968) suggested the renaming 
of regional lakes but this problem is beyond the scope of this re- 
port . 

The terminology for upland lakes in the Winooski and Lamoille 
Valleys seems hopelessly confused (see literature review by G. G. 
Connally in this guidebook) . For this reason, and because the 
upland lakes presented here differ substantially in number, extent, 
elevations, and drainage historv from previous reports, new names 
are used in most cases. Where possible, geographic features near 
outlet channels associated with newly defined lakes are utilized 
for the new names. The only exception is Lake Jericho, which was 
previously named by Connally (1966). 



324 



Upland Lakes 

Westward recession of the Laurentide ice margin uncovered 
successively lower outlets, resulting in progressive lowering of 
lake levels. Lakes Gillett, Huntington, Hollow Brook, Jericho 
Center, and Jericho developed in that order in the present Winoo- 
ski drainage basin, and in the present Lamoille basin were Lakes 
Gillett, Stowe, and The Creek (Figure 2) . Lake Gillett is the 
only lake that extended across the divide between the two present 
basins. The Lake The Creek outlet channel (Tl, Figure 3) extends 
southward to a delta complex representing Lakes Jericho and Jericho 
Center (JC2 and J8, Figure 3) indicating general time-equivalence 
of these lakes. Similarly, the Lake Jericho outlet channel (Jl, 
Figure 3) extends to the Coveville(?) level (C8, Figure 5) in the 
Champlain Valley, making it possible to relate the upland and re- 
gional lake histories. 

In addition to the relationship between upland lakes and the 
Laurentide ice margin, Mountain glacial features can be correlated 
with the upland lakes, as was previously described (Wagner, 1970). 
In terms of the lake names used here. Mountain glacier ice margin 
positions in Ritterbush Valley and North Branch Lamoille River Val- 
ley may be contemporaneous with Lake Stowe. 

Regional L2ikes 

The earliest regional lake in the Champlain Valley is repre- 
sented by the Quaker Springs (?) plane on Figures 1 and 3. The 
northern extent of this lake probaUaly terminated against the Laur- 
entide ice margin south of Burlington. Slightly older and more 
southerly ice margin positions in late Quaker Springs (?) time can 
be inferred by drainage relations. The delta at Bristol (Ql, Figure 
1) extends to an outwash surface heading in ice marginal glacial 
deposits south of Starksboro. The delta near South Hinesburg (Q2, 
Figure 1) indicates that the Laurentide ice sheet at that time 
blocked and diverted drainage in the Winooski River Valley through 
Hollow Brook Valley. 

The Coveville (?) water plane (Figure 3) formed immediately 
after the Quaker Springs level (Stewart, 1961). Chapman's (1937, 
Figure 16) Coveville plane is shown on Figure 3. The Coveville 
(?) plane drawn here on Figure 3 is based primarily on features in 
the Winooski Valley. Although the plane is below Chapman's, it 
does agree with features identified as Coveville by Connally (1966, 
19 70) in Vermont and by Denny (1969, personal communication) in New 
York. The previously described Lake Jericho drainage relations 
indicate that the Laurentide ice margin blocked the Winooski Valley 
in Coveville (?) time. Subsequent ice retreat, still in Coveville 
(?) time, is required for development of Coveville (?) features in 
the Winooski Valley (Figure 3) . Coveville (?) waters may have ex- 
tended northward to the Lamoille Valley (Connally, 1966) , and pos- 
sibly into Quebec (Parrott and Stone, this guidebook). 



325 



The Fort Ann level, first described by Chapman (1937), is the 
highest regional water-body widely marked by numerous shoreline 
features on Figure 3. Chapman's (1937, Figures 15 and 16) Fort 
Ann planes in Vermont and New York, although not coincident, brac- 
ket the plane drawn here (Figure 3) . The northern extent of the 
Fort Ann plane is uncertain. According to Chapman (19 37, p. 112- 
113) , and Parrott and Stone (this guidebook) , the ice margin re- 
treated north of the International Border in late Fort Ann time. 
McDonald (1968, p. 672-673) tentatively correlated strandline fea- 
tures in the Sherbrooke area of southeastern Quebec with the Fort 
Ann level. However, if the 230-foot elevation difference between 
the marine limit and Fort Ann strandlines in the Champlain Valley 
is compared with data in Quebec, then it appears that McDonald's 
features are about 25 feet too low to be an extension of the Fort 
Ann strandline from the Champlain Valley. As discussed below, it 
may be that Fort Ann time ended when Laurentide ice margin retreat 
exposed a low divide near Greens Corners, Vermont. 

To the south. Fort Ann features, extend beyond the study area 
(Calkin, 1965; Connally, 1970). Like Chapman's profile, the Fort 
Ann plane on Figure 3 projects southward to the vicinity of the 
present Hudson - Champlain divide near Fort Edward, some eight 
miles south of and at least ten feet higher than Chapman's spill- 
way at Fort Ann, New York. 

Below the Fort Ann but above the upper Champlain Sea planes 
are shoreline features which can be represented by a previously 
unrecognized water plane (Figure 3) . Southward extrapolation of 
this plane intersects the Champlain Valley floor below the divide, 
indicating drainage of the lake was northward. To the north the 
plane extends to a spillway near Greens Corners (Figures 1 and 3) . 
The name "Lake New York" was previously applied (Wagner, 1969) for 
northward draining lake water immediately below the Fort Ann level 
and cibove the Champlain Sea limit, although no specific plane was 
recognized. Because no evidence for this plane has as yet been 
found in New York (Denny, 1970, personal communication) , the name 
Greens Corners is applied rather than retain the name Lake New 
York. 

Evidence for a late Pleistocene marine invasion of the St. Law- 
rence lowland has long been recognized and is generally referred to 
as the "Champlain Sea"(Karrow, 1961). In the Champlain Valley fos- 
sils (chiefly mollusks) and in northern parts "sensitive clay" indi- 
cate the presence of sAline waters. Chapman (19 37, Figure 16) 
delineated a strandline marking the marine limit, which, as shown 
on Figure 3, differs somewhat from the fossil-based Champlain Sea 
maximum of this paper. The only evidence, albeit inconclusive, to 
support the marine limit based on fossils is the parallelism of 
this and other water planes, plus close agreement with the marine 
limit in New York (Denny, 1970, personal communication). A shell 
date for locality S88 (Appendix) basically agrees with the 12,000 
year age suggested by McDonald (196 8) for the marine maximum. 



326 



Below the marine limit Chapman recognized several marine water 
planes. Although the data on Figure 3 are inconclusive, there are 
alignments of features approximately coinciding with Chapman's 
(19 37, Figure 16) Port Kent and Burlington levels. In the Winooski 
Valley deltas are clustered at both the marine limit and at a some- 
what lower level (Figure 3) with a pronounced scarp intervening, 
supporting the Port Kent level (Johnson, 1970) . The Port Kent as 
a level is also supported by shell dates of about 11,300 yrs . B.P. 
from localities S14 and S24, although there is a discrepancy be- 
tween shell and wood dates at locality S24 (Appendix). Similarly, 
age dates from two marine shell localities (nos. S48 and S65) 
may document the Burlington level as a time line. In Quebec, Mc- 
Donald (196 8, p. 673) found marine shore features were best devel- 
oped at 115-140 feet below the upper limit, which approximately 
coincides with Chapman's Port Kent level. However, in northern 
New York, on the west side of the Champlain Valley, Denny (1969, 
personal communication) has mapped numerous Champlain Sea features 
with no apparent stillstand below the marine limit. Recent work 
with sediments submerged in modern Lake Champlain indicates the 
end of the Champlain Sea may have occurred about 10,200 years ago 
(Chase, 1972) . 



SPECULATIONS 

The early work of Chapman established a framework for the late 
Pleistocene history in northwestern Vermont. This framework is 
fundamental and likely will stand with little modification. Radio- 
carbon dates, although only from the Champlain Sea deposits in 
this area, tend to support Chapman's views. For events preceding 
and leading up to the Champlain Sea, there is some evidence that 
the succession of water bodies may not be as straightforward as 
generally believed. First, some of the deltas at the marine lim- 
it in the Missisquoi Valley, and to a lesser extent elsewhere, have 
complete or nearly complete surface and near-surface veneers of 
bottom-set sediment (Sl6j S26; S66; S68; S88) . Some other deltas 
at the marine limit have unusual thicknesses of topset sediment. 
Secondly, at least two of the marine limit deltas in the Missisquoi 
Valley have included bodies of till. Thirdly, in the northwestern 
part of the area are numerous exposures of till overlying a variety 
of sediments. Figure 4 is a speculative time-space diagram con- 
structed to account for these aspects. As shown, ice recession 
was accompanied by successive lowering of water levels in the clas- 
sical fashion, in other words, Quaker Springs, Coveville, Fort Ann, 
and Cheunplain Sea. Next, a minor oscillation of the ice margin 
temporarily reestablished a higher freshwater level, possibly the 
Fort Ann. At this time some of the previously formed Champlain 
Sea deltas were submerged and partly veneered with bottom-set sed- 
iment and till. 

Subsequent recession then lowered the water level to form Lake 
Greens Corners in the Champlain Valley south of the spillway at 



fi 



327 



d9 sjea/^ 



Ct 44»45' 




01 

a 

■H 
Xi 

n 

■c 
o 

■p 

Id 

iH 



C 0) 

•H C 

rO (0 

a. -a 

•H 

tj u 

C Q) 

(0 E 
•O 0) 

•p c 
w o 



>i4J 

"O 0) 
O 0) 

XI 5 

M - 
O O 

n] o 

> f^ 

r- 
•O 
C tJ^ 

O 

n to 

<o 

(0 

w 



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a) (1) 
•^^ o 

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u 

c 

0) 

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328 



Greens Corners. Because this 
at the marine limit in the Mis 
apparently had returned to its 
recession finally allowed for 
Champlain Valley, still at its 
oscillation is indicated in la 
till deposits in the northwest 
the positions of the ice margi 
southward oscillations. The i 
to show a possible relationshi 
land Front features (McDonald, 



spillway extends to a normal delta 
sisquoi Valley, the Sea by this time 

previous level in that valley. Ice 
the return of the Sea into all of the 

maximum level. Another ice margin 
ter Champlain Sea time, resulting in 

corner of the state. Figure 5 shows 
ns during the times of the positive, 
ce margins are extended into Quebec 
p with the Drummondville and High- 

1968) . 



329 




Figure 5; 



Ice margins in Champlain Valley 



(dotted lines), and Quebec (dashed lines; 
from McDonald, 1969, personal communication); 
Filled circles represent exposures of till 
overlying non-glacial sediment. 



330 



REFERENCES CITED 






Calkin, P. E. , 1965, Surficial geology of the Middlebury 15' quad- 
rangle, Vermont: Open-file report to Vermont Geological Sur- 
vey , 2 3 p . 

Chapman, D. H., 1937, Late-glacial and post glacial history of the 
Champlain Valley: Amer. Jour. Sci., v. 34, p. 89-124. 

Chase, J. S., 1972, Operation UP-SAILS : Sub-bottom profiling in 
Lake Champlain. M. S. dissertation. University of Vermont, 
104 p. 

Connally, G. G. , 1966, Surficial geology of the Mount Mansfield 
15' quadrangle, Vermont: Open-file report to Vermont Geologi- 
cal Survey, 37 p. 

, 1968, Surficial resources of the Champlain Basin, New York: 

manuscript, maps, and report to New York State Office of Planning 
Coordination, 111 p. 

, 19 70, Surficial geology of the Brandon-Ticonderoga 15-min- 

ute quadrangles, Vermont: Vermont Geol. Surv. , Studies in Ver- 
mont Geol. No. 2, 45 p. 

Johnson, P. H., 19 70, The surficial geology and Pleistocene his- 
tory of the Milton quadrangle, Vermont: M. S. dissertation. 
University of Vermont, 60 p. 

Karrow, P. F., 1961, The Champlain Sea and its sediments, in Leg- 
gett, R. F., ed. , Soils in Canada: Roy. Soc. Canada Spec. Pub. 
No. 3, p. 97-180. 

McDonald, B. C. , 1968, Deglaciation and differential post glacial 
rebound in the Appalachian region of southeastern Quebec: Jour, 
of Geol., V. 76, p. 664-677. 

Stewart, D. P., 1961, The glacial geology of Vermont: Vermont 
Geol. Surv. Bull. 19, 124 p. 

, and MacClintock, P., 1969, The surficial geology and Pleis- 
tocene history of Vermont: Vermont Geol. Surv. Bull. 31, 251 p. 

, and , 1970, Surficial Geologic Map of Vermont: Ver- 



4 



mont Geol. Surv. 

Wagner, W. P., 1969, The late Pleistocene of the Champlain Valley, 
Vermont: in. Guidebook for the Annual Mtg. of the New York State 
Geol. Assoc, p. 65-80. 



331 



r^Ai^^c^' ^^[^i^tocene Mountain glaciation, northern Vermont: 

Geol. Soc. America Bull., v. 81, p. 2465-2470. 

^^''^I'r ^'7 ^" l^''^' Environmental geology of the Huntington Val- 
ley, Vermont: M. S. dissertation. University of Vermont, 



332 



APPENDIX: Location and Description of Shoreline Features 



Feature Name 
and Number 

Gillett 1 



Type of 
Feature 



Elevation 
(feet) 



The 
Creek 



1 
2 
3 



Hunt- 1 
ington 

2 



outlet channel 760-780 



delta 



delta 



delta 



delta 



delta 

delta 

delta 
delta 



800-820 



800-820 



820-840 



800-820 



St owe 


1 


divide 


740-760 




2 


delta 


780-800 




3 


delta 


780-800 




4 


delta 


800-840 




5 


delta 


800-820 



outlet channel 700-720 
delta 720-740 
delta 700-720 



720-740 

740-760 

700-720 
700-740 



Location 
and Miscellaneous 

7.5 miles northeast of 
Gillett Pond; Hunting- 
ton quad. 

1.5 miles west of Stowe ; 
West Waterbury R. ; Mont- 
pelier quad. 

3.3 miles northeast of 
Stowe; Glen Bk . ; Montpel- 
ier quad. 

9 miles south of Johnson; 
Sterling Bk . ; Hyde Park 
quad. 

3.4 miles south of Morris- 
ville; Bedell Bk . ; Hyde 
Park quad. 

3.1 miles northeast of 
Stowe; Montpolier quad. 
Morrisville; Lamoille R. ; 
Hyde Park quad. 
0.8 mile southeast of 
Johnson; Lamoille R. ; 
Hyde Park quad. 
3 miles northeast of John- 
son; Gihon R. ; Hyde Park 
quad. 

Belvidere Jet.; North Br., 
Lamoille R. ; Hyde Park quad 

0.6 mile jouth of North 
Underhill; Underhill quad. 
Johnson; Lamoille R. ; 
Hyde Park quad. 
0.7 mile south of Jeffer- 
sonville; Brewster R. ; 
Jef fersonville quad. 
0.6 mile north of Water- 
ville; North Br. Lamoille 
R. ; Jef fersonville quad. 
Bakersfield; The Branch; 
Enosburg Falls quad. 

Huntington Ctr.; Brush Bk.; 
Huntington quad. 
1.7 miles southwest of 
Waterbury; Crossett Br.; 
Waterbuiry quad. 



333 



Feature Name 


Type of 


Elevation 


and Number 


Feature 


(feet) 


Hunt- 3 


delta 


700-720 


ington 






4 


delta 


740-760 


5 


delta 


720-740 


6 


delta 


720-740 


7 


delta 


700-760 



Hollow 1 
Brook 

2 



Jericho 1 
2 
3 



6 



outlet channel 660-680 
delta 660-680 



delta 



delta 



delta 



delta 



delta 



680-700 



700-720 



delta 620-640 
delta 640-660 
delta 620-640 



620-640 



620-640 



640-660 



7 outlet channel 660-680 

8 delta 690 



Location 
and Miscellaneous 

0.6 mile southeast of 
Huntington; unnamed 
stream; Huntington quad. 
1.3 miles northwest of 
Huntington; unnamed 
stream; Huntington quad. 
Waterbury Ctr.; Thatcher 
Bk.; Montpelier quad. 
3.8 miles northwest of 
Waterburv; Stevenson Br.; 
Bolton Mtn. quad. 
1.3 miles northwest of 
Moscow; Miller Bk . ; 
Montpelier quad. 

3 miles northeast of S. 
Hinesburg; Hinesburg quad. 
4.5 miles northeast of 
S. Hinesburg; unnamed 
stream; Hinesburg quad. 
1.3 miles south of Water- 
bury Ctr.; Thatcher Br.; 
Montpelier quad. 
3.8 miles northwest of 
Waterbury; Stevenson Br.; 
Bolton Mtn. quad. 

Huntington; Huntington R. ; 
Huntington quad. 
Waterbury; Winooski R. ; 
Montpelier quad. 
1.2 miles northwest of 
Huntington; unnamed 
stream; Huntington quad. 
1.5 miles northwest of 
Huntington; unnamed 
stream; Huntington quad. 
2.8 miles northwest of 
Huntington; unnamed 
stream; Huntington quad. 

3.8 miles northwest of 
Waterbury; Stevenson Bk . ; 
Bolton Mtn. quad. 

1.9 miles southwest of 
Williston; Essex Jet. quad. 
1 mile northeast of Jeri- 
cho; Browns R. ; Underhill 
quad. 



33^ 



Feature Name 


Type of 


Elevation 


and Mumber 


Feature 


(feet) 


Jericho 1 


outlet channel 


680-700 


Center 






2 


delta 


706 


Quaker 1 


delta 


560-580 


Springs 






(?) 2 


delta 


600-620 



Cove- 


1 


delta 


540-580 


ville 








(?) 










2 


delta 


580-600 




3 


delta 


560-600 




4 


delta 


580-600 




5 


delta 


605 




6 


delta 


600-620 




7 


delta 


620-640 




8 


delta 


600-620 


Fort 


1 


delta(?) 


380-400 


Ann 










2 


beach 


390-400 




3 


delta 


400-420 




4 


spit 


400-410 




5 


delta 


420-480 




6 


beach 


400-420 




7 


beach 


440-460 



Location 
and Miscellaneous 

Jericho Center; Richmond 

quad. 

Underhill; Browns R. and 

The Creek; Underhill quad. 

Bristol; New Haven R. ; 
Bristol quad. 
0.4 mile southeast of S. 
Hinesburg; Hollow Brook; 
Hinesburg quad. 

1.5 miles northwest of 
Richmond; Winooski R. ; 
Essex Jet. quad. 

1.5 miles north of Rich- 
mond; Mill Bk.; Richmond 
quad. 

0.4 mile south of Willis- 
ton; Allen Bk. ; Essex 
Jet. quad. 

2.6 miles northwest of 
Richmond; Winooski R. ; 
Essex Jet. quad. 

0.9 mile southwest of 
Jericho Center; unnamed 
brk.; Richmond quad. 
1.6 miles southeast of 
Jericho; Lee R. ; Rich- 
mond quad. 

at Jericho; Browns R.; 
Underhill quad. 



0.9 mile east of New Hav- 
en Mills; unnamed stream; 
South Mtn. quad. 
2.3 miles southeast of 
Vergennes; west side of 
Buck Mtn.; Monkton quad. 
0.6 mile south of Bris- 
tol; New Haven R. ; Bris- 
tol quad. 

4.1 miles northwest of 
Bristol; Monkton quad. 
0.8 mile east and north- 
east of Hogback Mtn.; 
Hinesburg quad. 
1.5 miles east of N. 
Ferrisburg; Mt. Philo 
quad. 

southwest side of Mt. 
Philo; Mt. Philo quad. 



l\\ 



335 



Feature Name 


and 


'•i umb e r 


Fort 


8 


Ann 






9 




10 




11 




12 




13 




14 



15 



Typo of 
Feature 

beach 

beach 

beach 

delta 

delta 
beach 
delta 

beach 



Elevation 
(feet) 

420-440 

400-420 

360-380 

380-400 

460-500 
400-460 
360-380 

480-500 



6 


beach 


440-460 


7 


beach 


440-500 


8 


bench 


480-510 



19 


delta 


500-520 


20 


delta 


480-520 


21 


delta 


500-540 


22 


delta 


500-525 


23 


delta 


530-550 


24 


beach 


520-540 


25 


beach 


520-580 


26 


delta 


520-540 



Location 
and Miscellaneous 

southwest side of Mt . 
Philo; Mt. Philo quad, 
southwest side of Mt. 
Philo; Mt. Philo quad, 
southwest side of Mt . 
Philo; Mt. Philo quad. 
1.9 miles southwest of 
S. Hinesburq; Lewis 
Creek; Hinesburg quad. 
South Hinesburg; Hollow 
Brook; Hinesburg quad, 
south side of Pease Moun- 
tain; Mt. Philo quad. 
1.9 miles southeast of 
Hinesburg; LaPlatte R. ; 
Hinesburg quad, 
four unnamed hillocks 
about 1.3 miles east of 
E. Charlotte; Mt . Philo 
quad. 

south side of Jones Hill; 
Mt . Philo quad. 
0.8 mile north3ast of 
East Charlotte; Mt . Philo 
quad. 

0.2 mile north of Rts . 
116 and 2A, intersection 
and north along Rt. 116; 
Mt. Philo and Burlington 
quads . 

Williston; Winooski R.; 
Essex Jet. quad. 
1.1 miles east of Essex 
Jet.; Winooski River; 
Essex Jet. quad. 
0.2 mile south of Jericho 
Cemetery; Lee R. ; Under- 
hill quad. 

Essex Center; Alder Brook; 
Essex Center quad. 
Brookside Cemetery; Rog- 
ers Brook; Essex Center 
quad. 

southeast side of Cobble 
Hill; Fort Ethan Allen 
quad. 

1.3 miles west of ?lilton 
Pond; Milton quad. 
2.5 miles north of West- 
ford; Browns River; Gil- 
son Mtn. quad. 



336 



Feature Name 
and Nxiinber 


Type of 
Feature 


Elevation 
(feet) 


Fort 2 7 
Ann 

28 


delta 
delta 


540-580 
540-560 


29 


beach 


520-560 


30 


delta 


560-580 


31 


delta 


600-620 


32 


beach 


590-610 



Greens 1 
Corners 

2 


delta 
beach 


200-220 
240-250 


3 


beach 


230-250 


4 


beach 


260 


5 


delta 


280-300 


6 


beach 


260-280 


7 


beach 


300-320 


8 


beach 


280-300 


9 


delta(?) 


300 


10 


beach 


280-300 


11 


delta(?) 


320-340 


12 


beach 


380-400 


13 


delta 


360-380 


14 


delta 


420-440 


15 


delta & 
outlet channel 


500-510 



Location i 

and Miscellaneous ' 

Fairfax Falls; Lamoille 
R. ; Gilson Mtn. quad. 
River View School; La- 
moille R. ; Gilson Mtn. 
quad. 

east side of Arrowhead 
Mtn.; Milton quad. 
Binghamville; Stones 
Brook; Gilson Mtn. quad. 
Buck Hollow; esker-fed; 
Milton quad. 
0.7 mile southwest of 
Bellevue Hill; St. Al- 
bans quad. 

Weybridge; Otter Creek; 

Middlebury quad. 

0.8 mile southeast of 

Vergennes; Monkton quad. 

0.8 mile northeast of 

Vergennes; Monkton quad. 

0.8 mile northeast of 

Ferrisburg; Monkton quad. 

0.5 mile southwest of 

North Ferrisburg; Lewis 

Creek; Mt. Philo quad. 

0.1 mile northwest of 

Coleman Corner; Mt. Philo 

quad. 

0.2 mile north of Coleman 

Corner; Mt. Philo quad. 

0.9 mile west of Mt. Philo; 

Mt. Philo quad. 

1 mile south of Prindle 

Corners; Lewis Creek; Mt. 

Philo quad. 

0.3 mile southeast of 

Barber Hill; Willsboro 

quad. 

0.4 mile northwest of 

Hinesburg; LaPlatte R. ; 

Hinesburg quad. 

1.9 miles southeast of 

Essex Jet.; Essex Jet. 

quad. 

1.4 miles southeast of 
Essex Jet.; Winooski R. 
Fairfax; Lamoille R. ; 
Milton quad. 

1.5 miles northeast of 
Greens Corners; St. Albans] 
quad. 



337 



Feature Name 
_and Num ber 

Champlain 
Sea 1 



15 



16 



17 



Typo of 
Feature 



delta 



delta 



beach 



delta 



delta 



Elevation 
(feet) 



100 



175 



3 


beach 


180-200 


4 


beach 


200-210 


5 


delta 


160-180 


6 


delta 


120-140 


7 


beach 


200-210 


8 


beach 


200-210 


9 


delta 


100-120 


10 


delta 


200-220 


11 


beach 


200-220 


12 


delta 


160-180 


13 


beach 


160-180 


14 


beach 


180-200 



240-260 



260-300 



260-280 



Location 
and Miscellaneous 



1.5 miles south of West 
Bridport; Crown Pt. 
quad.mollusks; 9,620 * 
350 B.P. shell date 
1-4695. 

1.3 miles southwest of 

Weybridge; Middlebury 

quad. 

3 miles north of Addison; 

Port Henry quad. 

5J.7 mile northwest of 

Buck Mt.; Monkton quad. 

1.6 miles west of V^r- 
qennes; Port Henry quad. 

2 miles northeast of Pan- 
ton; Port Henry quad. 
.2 mile northeast of Fer- 
risburg; Monkton quad. 
1.9 miles northeast of 
Ferrisburg; Monkton quad. 
» 1 mile east of Hawkins 
Bay; Port Henrv quad. 
1.2 miles southwest of 
North Ferrisburg; Mt. 
Philo quad. 

1.9 miles northwes'. of 
North Ferrisburg; Mt. 
Philo quad. 

1.5 miles west of North 
Ferrisburg; Mt . Philo 
quad. 

2.5 miles south of Char- 
lotte; Willsboro quad.; 
mollusks. 

1.8 miles southeast of 
Charlotte and west of 
Thompsons Point; Wills- 
boro quad.; mollusks; 
11,230*170 B.P. shell 
date 1-3647. 

.6 mile southwest of 
Jones Hill cemetery; 
Mt. Philo quad. 

1.9 miles southeast of 
Shelburne Falls; Mt. 
Philo quad. 

.9 mile south of Shel- 
burne Falls; Mt. Philo 
quad. 



i 



338 



Feature Name 
and Number 


Type of 
Feature 


Elevation 
(feet) 


Champlain 
Sea 18 


delta 


200-220 


19 


beach 


200-220 


20 


delta 


140-160 


21 


delta 


100-120 


22 


beach 


' 140-300 


23 


beach 


200-270 


24 


beach 


180-200 



25 



26 



27 



28 



29 



30 



31 



32 



beach 


280- 


-300 


delta 


280- 


-300 


delta 


320- 


-340 


delta 


320- 


-340 


delta 


300- 


-320 


delta 


180- 


-200 


delta 


160- 


-180 


beach 


320- 


-340 



Location 
and Miscellaneous 



.3 mile west of Shel- 
burne Falls; Mt. Philo 
quad. 

1.8 miles east of Shel- 
burne; Burlington quad.; 
mollusks . 

.3 mile northeast of 
Shelburne; Burlington 
quad. 

1.5 miles northwest of 
Shelburne; Burlington 
quad. 

.7 mile southeast of 
Twin Orchards; Burling- 
ton quad. 

.5 mile southeast of 
Queen City Park; Burling- 
ton quad. 

1.8 miles northeast of 
Queen City Park; Burling- 
ton quad.; mollusks and 
wood; 10,950*300 B.P. 
wood date W-2309; 11,420 
±350 shell date W-2311. 
1.5 miles southwest of 
South Burlington; Burl- 
ington quad. 
2 miles southeast of 
South Burlington on Rte. 
2; Burlington quad. 
.3 mile west of Ft. Ethan 
Allen Military Res.; Ft. 
Ethan Allen quad. 
1.1 miles northwest of Ft. 
Ethan Allen; Ethan Allen 
quad. 

1.5 miles northwest of 
Ft. Ethan Allen; Ethan 
Allen quad. 

.4 mile east of Shipman 
Hill; Ft. Ethan Allen 
quad. 

.4 mile southwest of 
Bayside; Ft. Ethan Allen 
quad. 

1.5 miles southwest of 
Colchester; Ft. Ethan 
Allen quad. 



339 



Feature Name Type of Elevation Location 

and Number Feature ( feet) and Miscellaneous 

Champlain 

Sea 33 delta 300-320 1.4 miles east of Col- 
chester; Ft. Ethan Al- 
len quad. 

34 beach 170-190 1.2 miles west of Bay- 

side; Ft. Ethan Allen 
quad; mollusks. 

35 delta 120-140 1.2 miles from tip of 

Malletts Head; Ft. Ethan 
Allen quad. 

36 beach 200-220 .8 mile from tip of Mal- 

letts Head; Ft. Ethan 
Allen quad. 

37 delta 300-320 1.4 miles north of Col- 

chester Pond; Essex 
Center quad. 

38 delta 190-200 .8 mile northwest of 

Chimney Corner; Ft. 
Ethan Allen quad. 

39 beach 250-270 .9 mile northwest of Wal- 

nut Ledge; Ft. Ethan Al- 
len quad, mollusks. 

40 delta 320-340 at Checkerberry Village; 

Georgia Plains; mollusks; 
10,520±180 B.P. shell 
date 1-4393. 
.8 mile south of Arrow- 
head Mtn. ; Milton quad. 
.7 mile south of Towns 
Corner School; Georgia 
Plains quad. 
.6 mile southwest of 
Silvertown School; Geor- 
gia Plains quad. 
.4 mile north of Arrow- 
head Mountain Lake; Mil- 
ton quad. 

.7 mile east of Milton- 
boro; Georgia Plains 
quad. 

.1 mile north of Milton- 
boro; Georgia Plains 
quad. 

.6 mile northwest of Mil- 
tonboro; Georgia Plains 
quad.; mollusks. 
1.2 miles northwest of 
Miltonboro; Georgia 
Plains quad.; mollusks; 
10,460*180 B.P. ; shell 
date 1-4394. 



41 


delta 


360-380 


42 


delta 


300-320 


43 


beach 


180-200 


44 


delta 


380-400 


45 


delta 


200-220 


46 


delta 


180-200 


47 


beach 


170-190 


48 


beach 


160-200 



3^0 



Feature Name 

and Number 


Type of 
Feature 


Elevation 
(feet) 


Champlain 
Sea 49 


beach 


300-320 


50 


beach 


190-220 


51 


delta 


240-260 


52 


delta 


230-240 


53 


delta 


180-200 


54 


delta 


380-400 


55 


beach 


380-400 


56 


delta 


380-400 


57 


beach 


300-320 


58 


beach 


180-200 


59 


beach 


390-400 


60 


delta 


380-400 


61 


beach 


310-320 


62 


beach 


220-230 


63 


beach 


180-200 


64 


beach (?) 


100-120 



65 

66 
67 



beach{?) 180-200 



delta 
delta 



400-420 
420-440 



Location 
and Miscellaneous 



2.5 miles southeast of 
Georgia Plains; Georgia 
Plains quad.; mollusks . 
1.5 miles west of Geor- 
gia Plains; Georgia 
Plains quad.; mollusks. 
at Georgia Plains; Geor- 
gia Plains quad. 
.6 mile southeast of 
rielville Landing; St. 
Albans Bay quad. 
1 mile northeast of 
Lime Rock Pt.; St. Al- 
bans Bay quad, 
at East Fairfield; Enos- 
burg Falls quad. 
.6 mile west of Holy 
Cross Cemetery; St. Al- 
bans quad. 

2.5 miles northwest of 
East Fairfield; Enosburg 
Falls quad. 

1 mile west of Holy Cross 
Cemetery; St. Albans quad, 

2 miles northwest of St. 
Albans; St. Albans quad. 
.1 mile east of I"7WSR rad- 
io tower; St. Albans quad. 
.5 mile north of Fair- 
field Station; Enosburg 
Falls quad. 

1.5 miles south of Fonda; 
St. Albans quad. 
.7 mile south of Fonda; 
St. Albans quad, 
at gravel pit Morin Road 
south of Swanton; East 
Alburg quad. 
1.5 miles southeast of 
Town of Isle La Motte; 
Rouses Point quad. ;mol- 
lusks . 

.7 mile north of Town of 
Isle La Motte; Rouses 
Point quad.; mollusks. 
at Sheldon; Enosburg 
Falls quad. 

at Enosburg Falls; Enos- 
burg Falls quad. 



i 



3^1 



Feature Ncune 
and Number 


Type of 
Feature 


Elevation 
(feet) 


Champlain 
Sea 68 


delta 


420-440 


69 


delta 


380-400 


70 


delta 


300-320 


71 


delta 


440-460 


72 


delta 


440-460 


73 


delta 


300-310 


74 


delta 


230-250 


75 


beach 


200-210 


76 


beach 


189 


77 


beach 


160-180 


78 


delta 


150-160 


79 


beach 


120-130 


80 


delta 


120-140 


81 


beach 


140 


82 


delta 


100-120 


83 


delta 


100-120 


84 


beach 


120-130 



85 

86 
87 

88 



beach 

delta 
delta 

delta 



300 

460-480 
440-460 

475 



Location 
and Miscellaneous 



.5 mile south of Enos- 
burg Falls; Enosburg 
Falls quad. 

at South Franklin; En- 
osburg Falls quad. 

1 mile west of Sheldon 
Springs; Enosburg Falls 
quad. 

Enosburg Falls; Enosburg 
Falls quad. 

at East Berkshire; Jay 
Peak quad. 

1.1 miles east of High- 
gate Ctr.; Highgate 
Ctr. quad. 

1.5 miles east of Swan- 
ton; Highgate Ctr. quad. 
.9 mile east of Swanton; 
Highgate Ctr. quad. 
.6 mile east of Swanton; 
Highgate Ctr. quad. 
1.5 miles west of Bluff 
Point; Rouses Point quad, 
at Swanton; Highgate Ctr. 
quad. 

1.3 miles west of Swanton; 
East Alburg quad. 

.4 mile north of Swanton; 
East Alburg quad. 

1.1 miles north of Swan- 
ton; Highgate Ctr. quad. 

1.4 miles northwest of 
Swanton; East Alburg quad. 
.5 mile west of Blue Rock; 
Rouses Point quad.,Tnollusks(?) 

1.2 miles northeast of 
West Swanton, East Alburg 
quad.; mollusks. 

1.3 miles southwest of 
Center Pond; Highgate 
Ctr. quad.; mollusks. 
.9 mile southwest of 
Richford; Jay Peak quad. 
.25 mile north of North 
Enosburg; Enosburg Falls 
quad. 

2 miles south of Freligh- 
sburg, Quebec; mollusks; 
11,740*200 B.P. shell 
date 1-4489. 



3^2 



Feature Name 
and Number 

Miscellaneous 
1 



Type of 
Feature 



spit? 

kame- 
delta 

delta 



kame- 
delta 

kame- 
delta 

kame- 
delta 

kame- 
delta 



Elevation 
(feet) 



500-520 
700-720 

640-660 

880-900 

740-760 

720-740 

900-920 



Location 
and Miscellaneous 



Mount Philo; Mt . Philo 
quad. 



1.1 miles e 

Hinesburg; 

quad. 

.7 mile eas 

Hinesburg; 

quad. 

1 . 3 miles n 

Jonesville ; 

quad. 

1 mile wes 

Hill School 

quad. 

1.1 miles s 

icho Ctr. ; 

quad. 

2 . 3 miles e 

Mansfield; 



ast of South 
Hinesburg 

t of South 

Hinesburg 

ortheast of 
Richmond 

t of Oak 

; Essex Jet. 

outh of Jer- 
Richmond 

ast of Lake 
Bolton quad. 



3^3 



PROGLACIAL LAKES IN THE LAMOILLE VALLEY, VERMONT 



by 



G. Gordon Connally 
State University of New York at Buffalo 



Three proglacial lakes were present in the Lamoille Valley 
during, and following, retreat of the late Woodfordian glacier in 
the Champlain Valley. This glacier deposited the Burlington drift 
of Stewart and MacClintock (1969). Although these lake levels 
have been recognized since the early part of this century, the nom- 
enclature is still confused, as seen in Table 1. This discussion 
is a summary of previously published works of others, and of field 
work performed sporadically for the past six years. Because the 
names Lake Lamoille and Lake Mansfield have priority in the Lam- 
oille Valley, they are retained in this paper. 



TABLE 1. 



MERWIN, 1908 




CHAPMAN, 19 37 
1942 


STfewAkl^, 1961 




Lake Laimoille I 







Lake Mansfield 




Lake Mauisfield 







Lake Lcimoille 




Lake Lamoille III 




Coveville Stage 
(LaUce Vermont) 


Coveville Stage 
(Lake Vermont) 






CONNALLY, 196 6 
1968 


STEWART AND 
MACCLINTOCK, 1969 


CONNALLY, 19 71 




Lake Lcimoille 


Quake 
(Lake 


r Springs Stage ? 
Vermont) 


Lake Lamoille 




Lake Mansfield 


Quake 
(Lake 


r Springs Stage ? 
Vermont) 


Lake Mansfield 




Coveville Stage 
(Lake Vermont) 


Coveville Stage 
(Lake Vermont) 


Lake Coveville 





3^ 



Merwin (1908) recognized an upper level (cibove 800'), 
designated Lake Lamoille I, that he thought had been restricted 
to the Lamoille Valley, He proposed that the lowland east of 
Mount Mansfield, between Morrisville and Stowe, was then cut down 
by steadily lowering lake waters, designated Lake Lamoille II. 
Then, when the outlet was breached to its present level (740') the 
waters of Lake Lcunoille II and Lake Winooski I, in the Winooski 
Valley to the south, joined to form Lake Mansfield. The lowest 
level in the Lamoille Valley (650'), presumed to have been restrict- 
ed to that valley, was named Lake Lamoille III. Fairchild (1916) 
recognized Merwin's terminology in the Lamoille Valley except that 
he erroneously projected his upper marine limit (the Champlain Sea) 
in place of Lake Lamoille III. Chapman (1937, 1942) projected the 
Coveville Stage of Lake Vermont to Merwin's Lake Lamoille II fea- 
tures, an interpretation that has been generally recognized to the 
present, the only change being the redesignation as Glacial Lake 
Coveville by Connally and Sirkin (1970). In mapping the bedrock 
geology of the Mount Mansfield quadrangle Christman (1959, p. 73) 
clearly recognized the priority of Merwin's terms although he 
chose "Lake Lamoille deposits" (quotations his) as a mapping unit, 

Stewart (1961) correctly inferred that the upper lake actu- 
ally extended into the Winooski Valley and was not restricted to 
the Lamoille Valley as Merwin (1908, p, 132) had supposed. He 
also inferred that the lower lake did not - an interpretation 
supported here - also contrary to the concepts of Merwin (ibid, 
p. 136). Stewart therefore honored the conceptual priority and 
renamed the upper lake, Lake Mansfield, and the lower. Lake Lam- 
oille, reversing Merwin's terms. Connally (1966, 1968), however, 
re-established Merwin's names, concluding that the original ele- 
vations and features were the most important precedent. Then, 
Stewart and MacClintock (1969) thoroughly confused matters by re- 
applying the names Lake Lamoille and Lake Mansfield to problemat- 
ical higher levels and by apparently assigning both of Merwin's 
levels to the Quaker Springs Stage of Lake Vermont, even though 
these lakes are not at the proper elevations (Connally, 1966, 
1968, and elsewhere) for the Champlain Valley lake. 

Merwin's original terminology is retained and defended here 
for three reasons: (1) these terms were accepted for more than 
50 years prior to the work of Stewart, (2) these terms were ap- 
plied to specific features and elevations that have been studied 
and restudied for more than 60 years, and (3) it is less confus- 
ing to either extend (Lake Lamoille) or restrict (Lake Mansfield) 
existing terms, when they are meaningful, than to introduce new 
names because of original conceptual flaws. 



GLACIAL LAKE LAMOILLE 

This lake is defined by six deltas in the Lamoille Valley 
and at least four between Morrisville and Stowe, east of Mount 



345 



Mansfield. Two of the deltas near Stowe were originally mapped 
by Wagner (1970, personal communication). The Lake Lamoille del- 
tas (Figure 1) range from 840' in the northwest to 780' in the 
southeast, as determined from flat delta tops depicted on 7 1/2' 
topographic maps. Lake Lamoille was blocked by the ice margin in 
the west and drained southward via the Winooski Valley. Wagner 
has located the outlet for this lake at about 760' at Gillett at 
the west end of the Winooski Valley, Figure 2 shows a projection 
of Lakes Lamoille, Mansfield, and Coveville along A-A' in Figure 
1. 



GLACIAL LAKE MANSFIELD 

This lake is defined by seven deltas and two beaches. The 
deltas (Figure 3) range from 760' in the north to 720' in the south. 
Merwin suggested that this lake coalesced with one in the Winooski 
Valley, however, the divide may be about 20' too high to have per- 
mitted this (Figure 2) . I suggest that initial drainage was through 
the Stowe lowland, while the ice blocked the valley of The Creek 
west of Mount Mansfield. Later, the ice block was dissected in The 
Creek and this channel controlled falling lake levels. The The 
Creek channel is at 700' and no shoreline features are graded to 
this elevation so it must have controlled a very short-lived lake 
level. Since Lake Mansfield is now defined only in the Lamoille 
Valley, this restricts the original definition of Merwin (1908). 

GLACIAL LAKE COVEVILLE 

This Icike is documented by nine deltas and two beaches (Fig- 
ure 4) that range from 660' to 640' at Morrisville. The inclusion 
of these features with Lake Coveville has never been challenged 
but it is fraught with problems as discussed by Wagner (1969). 
Connally and Calkin (1972) document the retreat of an active ice 
margin during Lake Coveville, including the Bridport readvance 
that took place between Burlington and Bridport (south of Middle- 
bury). The retreating margin of an active glacier may account for 
many of the problems outlined by Wagner. A projection of Lamoille 
Valley features onto a generalized north-south Lake Coveville pro- 
jection in the Champlain Valley strongly supports coincidence of 
the levels (Figure 5), 

TIME STRATIGRAPHY 

In Figure 5 a hypothetical projection of Lake Quaker Springs 
is shown. Both Lake Lamoille and Lake Mansfield had to drain south- 
ward into the Champlain Valley. If the projections are correct. 
Lake Mansfield must have drained into Lake Coveville (via Lake Jeri- 
cho in the Winooski Valley) and not Lake Quaker Springs. Perhaps 



3Jtf6 



Lake Mansfield was danuned by the Bridport readvance after a period 
of free drainage. Differential rebound (Figure 2) between Lake 
Lamoille and Lake Mansfield suggests that some event separated the 
two lakes and that Lake Lamoille drained through a series of im- 
pondments into Lake Quaker Springs at its northern boundary near 
Brandon. 

Connally and Sirkin (1972) have estimated the age of Lake 
Coveville as 12,800 yrs . B.P. and the Luzerne readvance, that they 
tentatively correlated with the Burlington drift, as 13,200 yrs. 
B.P. Thus, it is probable that Lakes Lamoille and Mansfield exist- 
ed sometime between 13,200 and 12,800 yrs. B.P. Because two of the 
local mountain glaciers reported by Wagner (19 70) can be directly 
related to Lake Lamoille; one in the Ritterbush Valley and one east 
of Belvidere Center, it is probable that these glaciers also exist- 
ed between 13,200 and 12,800 yrs. B.P. 

REFERENCES CITED 

Chapman, D. H. , 1937, Late glacial and post-glacial history of the 
Champlain Valley: Am. Jour. Sci., v. 34, p. 89-124. 

, 1942, Late glacial and post-glacial history of the Champlain 



Valley, Vermont: Vermont State Geologist, 23rd report, p. 48-83. 

Christman, R. A., 1959, Geology of the Mount Mansfield quadrangle, 
Vermont; Vermont Geol. Survey, Bull. 12, 75 p. 

Connally, G. G, , 1966, Surficial geology of the Mount Mansfield 
15 minute quadrangle, Vermont: Vermont Geol. Survey, open-file 
report, 33 p. 

, 1968, Glacial geology of the Mount Mansfield quadrangle, 



Vermont (abstr. ) : Geol. Soc. America, Spec. Paper 115, p. 256, 

, 1971, Pleistocene mountain glaciation in northern Vermont: 

oTscussion: Geol. Soc. America Bull., v, 82, p. 1763-1766, 

, and Calkin, P. E. , 1972, Woodfordian glacial history of the 

cFamplain lowland, Burlington to Brandon, Vermont, iji: N.E.I, 
G.C. Guidebook, 1972, Burlington. 

, and Sirkin, L, A., 19 70, Luzerne readvance near Glens Falls, 

tTew York: Geol. Soc. America Bull., v. 82, p. 989-1008. 

, and , 1972, The Wisconsinan history of the Hudson-Cham- 

pTain lobe : Geol. Soc. America, Special Paper (in press). 

Fairchild, H. L. , 1916, Post-glacial marine waters in Vermont: 
Vermont State Geologist, 10th report, p. 1-14. 



3^7 



Merwin, H. E. , 1908, Some late Wisconsin and post-Wisconsin shore- 
lines of northwestern Vermont: Vermont State Geologist, 6th 
report, p. 113-138. 

Stewart, D, P., 1961, The glacial geology of Vermont: Vermont 
Geol. Survey Bull. 19, 124 p. 

and MacClintock, P., 1969, The surficial geology and Pleis- 



tocene history of Vermont: Vermont Geol. Survey Bull. 31, 
251 p. 

Wagner, W. P., 1969, The late Pleistocene of the Champlain Valley, 
Vermont, in: Guidebook to Field Excursions, New York State 
Geol. Absoc, , Barnett, S. G. , editor, 41st annual meeting, p. 
65-76. 

, 19 70, Pleistocene mountain glaciation in northern Vermont: 



Geol. Soc. America Bull., v. 81, p. 2465-2470. 



3^8 




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352 



CONNALLY - WAGNER ROAD LOG 

Miles between Cumulative Description 

Points Mileage 

0.0 0.0 START Spear St. and Route 2. 

0.3 0.3 1-89 

1.2 1.5 Crossing the Winooski River. V 

0.6 2.1 Winooski Exit. 

0.6 2.7 St. Michaels College - Champlain 

Sea delta at the marine limit. 



1.2 3.9 Fort Ethan Allen (retired) on Cham- 

plain Sea delta. 

1.0 4.9 Essex Junction on Champlain Sea 

delta. 

0.3 5.2 North side of Essex Junction: note 

gully on contact between delta and 
till and lake sediment veneered 
bedrock upland. 

2.7 7.9 Essex Center on Lake Fort Ann del- 

ta. 

1.7 9.6 Descend from Lake Fort Ann delta 

to Browns River terrace. 

0.4 10.0 Cross Browns River. 

0,4 10.4 Lake Fort Ann delta remnant on left 

on till covered upland; note resi- 
dual boulders in gully. 

0.4 10.8 Lake Fort Ann surface at right a- 

cross Browns River. 

0.3 11.1 Cross Browns River. 

0.2 11.3 Village of Jericho on Lake Coveville 

delta. 

0.5 11.8 Ascend Lake Jericho delta. 

1.7 13.5 Leave Lake Jericho delta and con- 

tinue on the south terrace of Browns 
River that is graded to Lake Jericho. 



I 



353 



Miles between Cumulative Description 

Points Mileage 

0.2 13.7 Cross Browns River and ascend 

matching terrace on north; village 
of Underhill. Two sequences of 
ice contact drift on hillside on 
right. 

1.5 15.2 Cross The Creek; kame terraces on 

both right and left valley walls. 

1.7 16.9 Ice contact drift (kame terraces) 

on left and divide between south- 
flowing The Creek and a north-flow- 
ing tributary of the Lamoille Riv- 
er on the right. This divide is 
crucial in the correct interpreta- 
tion of Lamoille Valley lakes. 
The elevation is approximately 700 
ft.; too low for Lake Mansfield 
(720-740 ft.); and too high for 
Lake Coveville (640-660 ft.). 
Wagner has proposed this as an 
outlet for a lake he has named 
Glacial Lake The Creek. Clearly 
continental ice blocked this col 
during Lake Lamoille (840 ft.) and 
at least initial Lake Mansfield, 
and either retreated or was breach- 
ed prior to the establishment of 
Lake Coveville in the Champlain 
Valley. 

1.8 18.7 North Underhill; head of proposed 

spillway for Lake The Creek. Ice 
contact drift in valley bottom and 
on valley walls. 

5.8 24.5 Village of Cambridge; village is 

very close to 10 year floodplain. 

0.6 25.1 Cross Lamoille River. 

1.9 27.0 Cross Lamoille River; village of 

Jef fersonville. Follow Route 10 8 
south . 

1.6 28.6 STOP 1 (Connally) ; Three lake 

levels can De interred from the 
stream terraces and delta remnants 
in the Brewster River valleys. 



35^ 



Miles between Cumulative Description 

Points Mileage 

The lowest surface, to the north, 
has a sharp slope break at 660 ft. 
The one on which we stand has a 
broak at 740 ft. Higher terraces 
are graded to 840 ft. and a small 
delta remnant may be present at 
that elevation. The upper level 
has been assigned to Lake Lamoille, 
the intermediate to Lake Mansfield, 
and the lowest to Lake Cove vi lie. 
Here we will discuss the possible 
relationship between these lake 
levels and the The Creek divide. 

0.8 29.4 A 20 ft. high erosional scarp in 

the terraces graded to the 740 ft. 
delta. 

0.8 30.2 Village of South Cambridge; ascend 

the terrace graded to the 840 ft. 
level . 

1.9 32.1 Gravel pits that showed forset 

beds in 1965 and bottomset beds in 
1970. This delta documents an ear- 
ly local lake at about 1100 ft. 
dammed by the retreating continent- 
al ice margin. 

2.6 3 4.7 Protalus rampart (?) at north en- 

trance to Smugglers Notch; abundant 
talus and mudslide debris. 

2.9 37.6 Stream exposures of ice contact 

drift and till; collapse struc- 
tures. 

1.0 3 8.6 Kame deltas (?) or kame moraine (?) 

in vicinity of Toll House Inn, 
headwaters of the Waterbury River. 

3.8 42.4 Holme Lodge - valley bottom floor- 

ed with more than 100 ft. of un- 
consolidated material. 

0.2 4 2.6 Leave Route 10 8; make sharp right 

turn and follow signs to Trapp 
Family Lodge. 



355 



Miles between Cumulative Description 

Points Mileage ___^_ 

0.5 43.1 Ten Acres Lodge on 800 ft. delta 

assigned to Glacial Lake Gillett 
by Wagner. 

1.6 44.7 STOP 2 (Wagner) : Trapp Family 

Lodge. Just beyond Lodge is good 
view of Miller Brook Valley. Pho- 
to stop. 

1.7 46.4 Continue on dirt road to black 

top, make right turn immediately, 
onto dirt surface. Cross Miller 
Brook and take first right. 

1.8 4 8.2 STOP 3 (Wagner) : Phase I Mountain 

glaciation! Park cars in field 
across from house and walk up dirt 
road onto delta surface. Delta 
was constructed from outwash with 
stagnant ice margin up valley. 

Proceed up valley to Lake Mansfield 
Trout Club. 

2.2 50.4 STOP 4 (Wagner) : Phase II Mountain 

glaciation. Walk across dam breast 
and follow white blazed trail to 
lateral moraine. Note swamp area 
formed between lateral moraine and 
hillside. Auger holes indicate 11 
ft. of peat. Note also boulder in 
swamp with high water surface marks 
that show differential rotation. 
Slightly further down valley is end 
moraine. In addition to such fea- 
tures as previously reported, other 
end moraines have now been found at 
Noyes Pond, Pigeon Pond, Spring 
Lake, Lakota Lake, and Crook Brook 
indicating widespread Mountain gla- 
ciation in Vermont. 

Lunch, and then return to cars, 
proceed back down valley crossing 
Little River. 

8.6 59.0 Join Route 100 north. 

2.9 61.9 Stay on Route 100 through Stowe 

village . 



356 



Miles between Cumulative Description 

Points Mileage 

3.2 65.1 Bear right leaving Route 100. 

1.8 66.9 The first of a series of four del- 

tas, some slightly pitted, that 
crest between 780 and 800 ft. 
These have been assigned to Lake 
Lamoille by Connally and to Lakes 
Gillett and Stowe by Wagner. 

0.9 67.8 Road bends sharply left. 

3.6 71.4 Sharp right turn ascending exten- 

sive 780 ft. delta deposited by 
upper Lamoille River. 

1.3 72.7 Turn sharply back to left. 

0.5 73.2 STOP 5 (Connally) : From this van- 

tage ~poTnt~Thi~~T80 ft. delta can 
be seen in the foreground and a 
partially collapsed or dissected 
720 ft. delta can be seen in the 
distance at Hyde Park. In addi- 
tion, small deltas are present 
from Morrisville to Johnson at 640 
ft. The upper level is assigned 
to Lake Lamoille, the intermediate 
to Lake Mansfield, and the lowest 
to a Lake Coveville inlet. Wagner 
has assigned the upper level to 
Lake Gillett and the intermediate 
to Lake The Creek. We will dis- 
cuss the relationship of the three 
levels to the Lake Gillett spill- 
way. 

Continue toward Morrisville. 

1.0 74.2 Morrisville, turn right on Route 

100. 

0.2 74.4 Cross Lamoille River. 

0.9 75.3 Take Route 15 west. 

4.0 79.3 A 740 ft. delta on the south edge 

of the village of Johnson. 



I 



357 



Miles between Cumulative Description 

Points Mileage 

0.7 80.0 Bear right on Route 100 in Johnson 

and continue north. 

1.8 81.8 Another dissected 740 ft. delta 

just east of East Johnson. 

1.2 83.0 An extensive delta that crests at 

840 ft. was deposited here by the 
Gihon River. 

2.0 85.0 Village of North Hyde Park. 

2.7 87.7 Turn left on dirt road; note broad 

outwash surface. 

1.5 89.2 STOP 6 (Wagner) ; Gravel pit in 

Phase I Mountain glaciation, Ritter- 
bush Valley. 

Continue northward for 200 ft. and 
take dirt road to the left. 

1.0 90.2 STOP 7 (Wagner) : Ritterbush Pond; 

Phase II Mountain glaciation. Here 
we will examine the end moraines in 
Ritterbush Valley. 

Return to dirt road near Stop 6, 
turn left and continue northward. 

1.0 91.2 View through trees to left of Rit- 

terbush Pond cirque. 

2.2 93.4 Enter Belvidere Pond cirque. 

0.5 93.9 STOP 8 (Wagner) ; Scenic overlook 

and parking lot; Phase II Mountain 
glaciation. This is the Belvidere 
Pond cirque, "tarn", and end mor- 
aine. 

Continue west. 

1.4 95.3 Junction Routes 109 and 118. Fol- 

low Route 109 south. 

2.1 97.4 Gravel pit to left in Phase I Bel- 

videre Valley Mountain glacier fea- 
tures . 



358 



Miles between Cumulative Description 

Points Mileage 

1.0 9 8.4 Outwash plain (?). 

0.5 98.9 Village of Belvidere Center. 

2.1 101.0 STOP 9 (Connally) : Pitted out- 

wash IS present almost certainly 
as a result of the Belvidere Pond 
glacier with possible additions 
from a local glacier immediately 
north of the stop. Although the 
surface elevation is only 800 ft. 
here it rises to 840 ft. to the 
north. Thus, Connally assigns 
this feature to Lake Lamoille, 
suggesting that local Mountain 
glaciation can be correlated with 
Glacial Lake Lamoille. Kettles 
are not present in Lake Mansfield 
deposits suggesting a very short- 
lived episode of local glaciation. 

Continue south. 

3.8 104.8 Village of Waterville. 

4.8 109.6 Junction with Route 108. Follow 

Route 10 8 south. 

0.4 110.0 Junction with Route 15. Follow 

Route 15 west to Jef fersonville 
and from there to Burlington. 

28.4 138.4 END OF TRIP. 



359 



Trip G-3 

STRANDLINE FEATURES AND LATE PLEISTOCENE 
CHRONOLOGY OF NORTHWEST VERMONT 



William R. Parrott 
Department of Geology 
Bryn Mawr College 
Bryn Mawr, Pennsylvania 
19010 



Byron D. Stone 
Department of Geography 
and Environmental Engineering 
The Johns Hopkins University 
Baltimore, Maryland 21218 



Introduction 

On this field trip we will examine early Holocene Champlain 
Sea strandlines along Lake Champlain; then we will see late Pleis- 
tocene glacial and glacial lake deposits that indicate both active 
and stagnant ice retreat in the northern Champlain Valley. Figure 
1 is a location map indicating the area under consideration; Fig- 
ure 2 is a map of the surficial geology of the Enosburg Falls quad- 
rangle; Figure 3 is a north-south plot of features in the north- 
eastern part of the Champlain Valley and adjacent Quebec including 
data from Wagner (this guidebook. Figure 3, p. 322) and McDonald 
(1968) . 

Deglaciation of this region began with the retreat of the 
Laurentide ice sheet from the Green Moxin tains and Champlain Valley; 
in the latter there was apparently a lobe of ice which would per- 
sist in form as the ice retreated both northward and away from the 
Green Mountain front. Stewart and MacClintock (1969) discuss the 
first high-level proglacial lakes to form accompanying initial de- 
glaciation. The presence of local mountain glaciation near Belvi- 
dere, Vermont (Wagner, 1970, 1971; Stewart, 1971; Connally, 1971) 
does not appear to influence deposits or events in the region un- 
der discussion here, other than being the source of outwash waters 
supplying sediment. 

As deglaciation proceeded, large proglacial IcOces gradually 
formed in the Champlain Valley at the ice margin, forming various 
stages of Glacial Lake Vermont, the two principal phases of which 
were the Coveville and Fort Ann phases, named for their presumed 
outlets in New York. Work done reported in this article confirms 
suggestions by McDonald (196 8) and by Stewart and MacClintock 
(1969) that these water levels may have been confluent between the 
Champlain Valley and the area of southeastern Quebec studied by 
McDonald. It is proposed that the upper level, the "Sherbrooke 
phase" of Glacial Lake Memphreraagog (McDonald, 1968) , is at least 
in part correlative with a corresponding level in the Champlain 
Valley, probably the Coveville phase of Lake Vermont of Chapman 
(19 37) , and that the lower phase described by McDonald is correla- 
tive with the Fort Ann phase of Glacial Lake Vermont. Features to 
the south (see Wagner, this guidebook. Figure 3, p. 322) , corres- 



360 



ponding reasonably well to the Coveville level of Chapman, are 
traceable from the vicinity of Jef fersonville and BeOcersfield, 
Vermont (at 720-740 ft.) north and northeastward up into the 
Missisquoi basin along the mountain front, and thence up the 
North Branch of the Missisquoi to the vicinity of Bolton Center, 
Quebec and the Lake Nick col (817 ft.) described by McDonald (1968, 
p. 668-669). Features belonging to a lower plane, approximately 
120-140 feet below the first are likewise traceable from Jefferson- 
ville and Bakersfield (600 ft.) up through the Missisquoi Basin and 
Sutton Valley to Lake Brome, Quebec. The data, when plotted on a 
north-south section, form two fairly well-defined curves (Figure 3) . 
McDonald (1968) envisions the Cherry River moraine ice holding back 
the waters of the Sherbrooke phase of Glacial Lake Memphremagog, 
then the retreat of the ice beyond the Sutton Mountains, permitting 
the water level to drop to the lower level, possibly confluent with 
Fort Ann waters; he also notes (p. 692) that the lower lake system 
was already in existence at the ice front when the Highland Front 
moraine was developed. It should be noted that the northernmost 
point plotted in this article on the upper plane (Coveville-Sher- 
brooke) , No. 20, is a well developed delta on the southeast flank 
of the Brome-Spruce-Pine mountain area, showing topset-foreast con- 
tact at 825 feet; this vicinity would have to be free of ice be- 
fore Ft, Ann time. On the whole, the findings reported here agree 
with those of McDonald (1^68). 

Several things should be noted about Figure 3. First, all 
points are projected westward, and of necessity involve scatter 
due to the width of the area considered, and the fact that the 
isobases do not trend directly east-west. The curves appear to 
level off northward, as the locations gradually shift to the 
northeast, becoming more parallel to the isobars. Also, the ele- 
vations were determined using topographic maps and bench marks, 
and of necessity involve both variation and error. 

Below the second curve there are a number of features which 
appear to represent levels intermediate to those of the Champlain 
Sea. These are best displayed in the Enosburg Falls quadrangle, 
between the towns of Enosburg and Bakersfield along Vt. Rt. 108, 
where a set of well defined multiple terraces can be seen (Points 
4, 5, 24, 46-49 on Figure 3); these may correspond to intermedi- 
ate phases between Glacial Lake Vermont and the Champlain Sea, 
"Lake New York" of Wagner (1969). 

Marine waters entered the isostatically depressed Champlain 
Valley following retreat of the Laurentide ice mass from the St. 
Lawrence Valley. The oldest marine shell date in the Champlain 
Valley is from the marine shells at Stop 6, the gravel pit 2 miles 
south of Frelighsburg, Quebec, dated at 11,740*200 years B.P. The 
highest marine strandline in the valley proper is straight and 
parallel to higher (older) proglacial lake water planes (Chapman, 
1937; Wagner, 1972). Recent shell dates of lower (younger) marine 
shoreline deposits allow correlation of these features. Lower 



361 




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LEGEND 



ALLUVIUM 



I 9 I FLUVIAL GRAVEL 
I 6 I SWAMP DEPOSITS 



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MARINE SEDIMENTS 
7 Sand ond Gravtl 
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AND BEDROCK 



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SCALE 1 162500 

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SURFICIAL GEOLOGY OF THE ENOSBURG FALLS QUADRANGLE 



Figure 2 



W. R. PARROTT 1971 



363 



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364 
TABLE 1 

NUMBERED LOCALITIES PLOTTED ON FIGURE 3 



Number 


Feature 


Town or Township 


Elevation 


(feet) 


1. 


delta 


Bakersfield, Vt. 


720-740 




2. 


delta-terrace 


Bakersfield, " 


720-740 




3. 


beach deposits 


Enosburg, " 


740 




4. 


beach deposits 


Enosburg, " 


740 




5. 


beach deposits 


Enosburg, " 


740 




6. 


delta 


Montgomery, " 


720-740 




7. 


delta 


Enosburg, " 


740 




8. 


delta 


Richford, 


760 




9. 


delta 


Richford, 


740-760 




10. 


terrace 


Troy, 


720-740 




11. 


delta 


Richford, 


760 




12. 


delta 


Richford, 


760 




13. 


delta 


Richford, 


740-760 




14. 


delta 


Potton, Que. 


750 




15. 


delta 


Potton, " 


750-775 




16. 


delta 


Potton, " 


775-800 




17. 


delta 


Sutton, 


750-775 




18. 


terrace 


Sutton, " 


750-775 




19. 


delta-terrace 


Bolton, " 


800 




20. 


delta 


Brome, " 


825 




21. 


delta-terrace 


Bakersfield, Vt. 


600 




22. 


terrace 


Bakersfield, " 


600 




23. 


beach deposits 


Enosburg, " 


600 




24. 


terrace 


Enosburg, " 


600 




25. 


terrace 


Montgomery, " 


600-620 




26. 


terrace 


Montgomery, " 


600 




27. 


terrace, delta 


Richford, " 


600-620 




28. 


beach deposits - terrace 


Troy, 


600-620 




29. 


delta-terrace 


Richford, " 


640-660 




30. 


delta 


Sutton, Que. 


625 




31. 


terrace 


Potton, " 


600-625 




32. 


terrace 


Potton, " 


600-625 




33. 


terrace 


St. Armand, Que. 


600-625 




34. 


terrace 


Potton, " 


600-650 




35. 


terrace-(delta?) 


Sutton, " 


625 




36. 


terrace 


Dunham, " 


625-650 




37. 


terrace 


Dunham, " 


625-650 




38. 


terrace-(delta?) 


Dunham, " 


625 




39. 


terrace 


Potton, " 


650-675 




40. 


terrace 


Sutton, " 


625-650 




41. 


terrace (delta?) 


Dunham, " 


625-650 




42. 


delta? 


Sutton, " 


650 





365 



Number 



Feature 



43. 


terrace 


44. 


terrace 


45. 


terrace 


46. 




46. 


terrace 


47. 


terrace 


48. 


terrace 


49. 


terrace 


50. 


terrace 


51. 


delta 


52. 


delta 


53. 


delta 


54. 


delta 


55. 


delta 


56. 


delta 


57. 


delta 


58. 


terrace 


59. 


delta 


60. 


delta 


61. 


delta 


62. 


delta 


63. 


delta 



Town or Township 


Elevation 


Brome, 


Que. 


650-675 


Brome, 


II 


650 


Brome, 


II 


650-675 


Enosburg, 


Vt. 


550 


Enosburg, 


" 


520 


Enosburg, 


II 


490 


Enosburg, 


11 


450 


Enosburg, 


II 


480 


Fairfield, 


II 


380-400 


Fairfield, 


II 


400 


Fairfield, 


M 


380-400 


Sheldon, 


II 


400-420 


Enosburg, 


II 


420-440 


Enosburg, 


II 


440 


Sheldon, 


II 


380-400 


Enosburg, 


M 


440 


Berkshire, 


11 


440-460 


Richford, 


M 


460-480 


Berkshire, 


11 


440-460 


St. Armand, Que. 


450-475 


Sheldon, 


Vt. 


300 



366 



strandlines show less tilt, indicating that crustal rebound began 
during the marine episode. Models and details of isostatic ad- 
justment will be discussed at the first stop. 

On Figure 3 a number of points related to the Champlain Sea 
have been plotted; however, data in the literature on Quebec are 
scanty and have not been included. It should be noted that the 
marine maximum of 540 feet noted by McDonald (1968, p. 673) fits 
the plot well and maintains parallelism with the upper two planes. 
In addition, the well developed features noted by McDonald at 400- 
420 feet appear to be characteristic of this area as well, although 
they vary up the Missisquoi basin from 380-400 feet in the west to 
420-440 feet in the east. 

The sequence of deglaciation affecting the influx and history 
of the Champlain Sea, however, now appears to be more complex than 
originally contemplated. Some workers (Cannon, 1964; Stewart and 
MacClintock, 1969) have proposed an intermediate period of subar- 
eal weathering between the Glacial Lake Vermont and the Champlain 
Sea; recent work by McDonald (1963) , Johnson (1970) , Wagner (per- 
sonal communication) and the present study have not detected any 
weathering zone. However, mappings by Wagner in the St. Albans 
and Jay Peak Quadrangles, and by Parrott in the Enosburg Falls and 
Jay Peak Quadrangles have revealed the presence of a till within 
Champlain Sea sediments in the Missisquoi and Champlain Valleys. 
Shells found in the Frelighsburg, Quebec pit showing possible dis- 
turbance of the deltaic deposits there may record this readvance. 
The kame complex at Berkshire, Vermont is essentially surrounded 
by the till, but shows no evidence of disturbance itself, and 
appears to be related to the wasting away of the ice of this re- 
advance. It is proposed that this readvance be tentatively named 
the "Missisquoi readvance," as the Missisquoi basin marks its ap- 
parent southern limit. 

In all, deglaciation appears to have been at first character- 
ized by active retreat, and ended in stagnation-zone retreat with 
the wasting of the Missisquoi ice. 



Acknowledgements 

We give special thanks to James Morse of the University of 
Vermont for assistance in the field and in the preparation of this 
article. We also gratefully acknowledge W. Philip Wagner for his 
advice and guidance in the course of the authors' research, as 
well as numerous other individuals who made the study possible. 
Gail Schwartz receives special thanks for typing the manuscript. 



367 

MAPS 



Road Map 

Vermoni'* 

U.S.G.S. 

1 ;250, OOP 

Lake Champlain NL 18-12* 
15 Minute Quadrangles 

Milton 

St. Albans 

Enosburg Falls* 

Jay Peak 

Irasburg 

Mt. Mansfield 

7 1/2 Minute Quadrangles 

Milton 

Georgia Plains* 
St. Albans Bay* 
St. Albans* 
Highgate Center* 

Canadian (obtainable from the Map Distribution Office 

Department of Mines and Technical Surveys 
Ottawa) 

1 ;50a OOP 

Ottawa-Montreal NW 44/76 
1 :25P, PPP 

Montreal 31 -H 
1 :5P, PPP 

Sutton 31 H/2 West 
Sutton 31 H/2 East 
Granby 3 1 H/7 East 
Memphremagog 31 H/1 West 



* Suggested for field trip 



368 



Mileage 




Cum. 



S/S 



0.3 


0.3 


0.8 


0.5 



Road Log for Trip G-3 

Trip will assemble in parking lot of University of Vermont College 
of Medicine, off of East Avenue. TRIP LEAVES AT 8:30 A.M. SHARP! 
AT STOPS, PARK CARS AS FAR OFF ROAD AS POSSIBLE. 



Road log begins. Leave College of Medicine parking 
lot and turn right onto East Avenue. 

Intersection with U.S. Rt. 2; turn left onto Rt. 2. 

Intersection with 1-89 entrance; enter on right, 
after crossing over the interstate, heading north 
toward St. Albans. 

1.9 1.1 Note marine delta sands in South Burlington landfill 
on right. 

2.4 0.5 Note Winooski River gorge on right; 60 feet downcut- 
ting into dolostone bedrock since recession of Cham- 
plain Sea. 

10.6 8.2 Milton Exit ; turn left at end of exit ramp, proceed 

.1 mi. (E) , turn left (N) on U.S. Rt. 7. ENTER MILTON 
7 1/2' Quadrangle. 

14.0 3.4 The southern end of the village of Milton sits on a 

maximum Champlain Sea delta (360' elevation). Note 
extensive delta flat north and northwest of the 
village. 

16.7 2.7 Follow Rt. 7 through the village of Milton, noting 

unique pivot-gate dam at south end of Arrowhead 
Mountain Lake. 

17.5 0.8 Lake Road. Turn left (W) . Continue west and north. 
ENTER GEORGIA PLAINS 7 1/2' Quadrangle. 

2 J. 5 6.0 Bear left (W) on Lake Road. 

24.8 1.3 You are crossing the Champlain Thrust contact: Dun- 

ham over Beldens(?); upper plate forms fault scarp 
along east shore of Lake Champlain. 

2 5.0 0.2 Sharp right turn; proceed north to: 

26.1 1.1 STOP 1. Champlain Sea beach deposit, 160' elevation, 

C-14 date 10,460 years B.P. on Macoma balthica shells. 
Note washed, Imbricate structure of beach gravels. 



369 



Mileage 

Cum. S/S 

What factors could influence the shell C-14 date 
here ? Discussion of models and details related 
to isostatic adjustment. 

Continue north along the lake. ENTER ST. ALBANS BAY 
7 1/2' Quadrangle. 

32.3 6.2 Melville Landing; turn right (SE) . 

32.8 0.5 Note delta (240' elev.) south of the road; this 

delta is above the projected 10,460 year-old 
strandline. 

33.2 0.4 Turn loft ; Proceed north to Mill River. 

35.2 2.0 Mill River; note downstream incision, well-devel- 
oped floodplain and modern delta. 

37.4 2.2 Proceed north to Vt. Rt. 36, St. Albans Bay; turn 

right . 

38.2 0.8 Kellog Road; turn left (N) . Is there beach topo- 
graphy along this roiH" ? ENTER ST. ALBANS 7 1/2' 
Quadrangle. 

41.9 3.7 Railroad crossing. Beach, wavecut topography on 

right. 

Proceed 0.2 miles east to Route 7; turn right (S) . 

Intersection Vt. Rt. 105; turn left (E) . 

Intersection at Greens Corners; turn right (E) . 

Bear left at fork in road (NE) . 

STOP 2. Greens Corners delta and associated chan- 
nel Gravel is in kame delta or kame terrace form- 
ed when the Laurentide ice margin impinged against 
the upland. Till occurs at and near the top of the 
section in places. Similar till also is found at 
and near the land surface in the field to the west, 
and in many other localities north and northwest of 
this site. Northeast of this locality is a linear 
valley which now is occupied by a small stream. The 
gravel pit is at the divide, and is the northernmost 
location of Lake Greens Corners (Wagner, this guide- 
book). At least two other distinct channels, also 
approximately coincident with the water plane of 



42.1 


0.2 


44.7 


2.6 


48.2 


3.5 


48.6 


0.4 


49.8 


1.2 



370 



Mileage 

Cum. S/S 

Lake Greens Corners, occur in the upland area to 
the northwest. All of the above channels can be 
traced northeastward into the Missisquoi Basin 
where they extend to the level of deltas at the 
marine limit. Apparently, drainage from Lake 
Greens Corners was controlled by these channels in 
Champlain Sea time. 

Proceed northeast along channel and railroad tracks. 
ENTER ENOSBURG FALLS 15' Quadrangle. 

53.2 3.4 Intersection with Vt. Rt. 105; turn right (E) . 

54.5 1.3 Intersection with road to Sheldon; turn right (S), 
onto it. 

55.2 0.7 Sharp turn in road off to right (S) ; proceed straight 
ahead (E) onto dirt road, crossing: a. Black Creek 
bridge, and b. railroad. 

55.5 0.3 STOP 3. Gravel pit in Champlain Sea deltaic mater- 
ial. Sand pit exposes deltaic sand of the marine 
limit Black Creek delta. In the eastern wall of the 
pit are exposed several feet of till overlying the 
deltaic materials. To the south the topset level of 
the delta is well-defined but the surface deposits 
are bottomset silt and clay. One well in the region 
penetrates through the silt-clay material which ov- 
erlies sand. The delta is believed to be an early 
Champlain Sea feature with overlying lacustrine sed- 
iments from a temporary lake. The till is taken as 
evidence of glacial control for the lake. 

Return to Rt. 105 via route just taken. 

56.5 1.0 Intersection with Rt. 105; turn right (E) . 

56.9 0.4 Cross Missisquoi River. 

60.8 3.9 Intersection with Vermont Rt. 78; turn left (N) . 

East Highgate; sharp turn to right (N) . ENTER HIGH- 
GATE CENTER 7 1/2' Quadrangle. 

62.2 1.4 Intersection with small road off to left; turn left 

(SW) . 

63.1 0.9 STOP 4. Champlain Sea delta gravel pit; Sand and 
gravel pit on Champlain Sea sediments at the Port 
Kent level of Chapman (1937). 



I 



371 



Mileage 




Cum. 


S/S 


64.0 


0.9 


64.7 


0.7 


66.8 


2.1 


61.1 


0.9 


70.6 


2.9 


71.0 


0.4 


72.8 


1.8 



Return to intersection with Rt. 78. 

Turn left (W) onto Rt. 78. 

Beaulieus Corner; turn right (sharp) , to northeast. 
RE-ENTER ENOSBURG FALLS QUADRANGLE. 

You are now crossing a plain of Champlain Sea sedi- 
ments, with several bedrock islands exposed. 

Browns Corners. Proceed straight ahead (E) . Stay 
on main road. 

Franklin; intersection with Vt. Rt. 120. Turn left 
(N). 

4 Corners; bear right, following Rt. 120 (E) . 

Lake Carmi. This lake rests in a valley containing 
only bedrock, till, and Champlain Sea sediments; 
now draining to the north, it originally drained 
southward following the Champlain Sea influx. 

74.3 1.5 Intersection with road to right (on south); turn 
right . 

7 7.4 3.1 STOP 5. LAKE CARMI STATE PARK. LUNCH. Time for 
discussion. 

Return to Rt. 120. 

82.3 4.9 Intersection with Rt. 120; bear right (ahead) (N) . 

83.7 1.4 East Franklin; sharp turn to right (E) . 

84.2 0.5 Intersection with Vt. Rt. 108; turn left (N) . 

85.6 1.4 International Border; we will stop to be cleared as 
a group. Please refrain from having any items in 
your vehicle which might be a source of grief . 

86.9 1.3 STOP 6. Gravel pit 2 miles south of Frelighsburg, 
Quebec. Refer to discussion above. Deltaic mater- 
ial here contained a lens of sand and clay contain- 
ing disturbed Ma coma balthica which dated at 11,740 
±200 years B.P, 

Return to Rt. 108; turn right (S) . 



372 



Mileage 

Cum. S/S 
MTT ITT 



89.5 1.4 

90.1 0.6 

90.3 0.2 
90.5 0.2 

92.2 1.7 

92.8 0.6 

92.9 0.1 

93.4 0.5 



Re-cross International Boundary; we will stop to 
be let back into the United States. 

Intersection of Rt. 120 with Rt. 108; bear left , 
toward West Berkshire (S) . 

Gravel pits in gorge to right contain fluvial gra- 
vels; This area drained an upland lake which we 
will see shortly. 

West Berkshire. 

Intersection with dirt road on right (S) side of Rt. 
108. Turn right . 

You are now driving through a kame field mantled by 
lacustrine sediments; drainage was down through the 
gorge we just came through. 

Intersection with road between Berkshire and Enos- 
burg Falls. Turn right (S) . 

The hills in front of you are part of the massive 
kame field in this area. 

STOP 7. Gravel pit in Berkshire kame field. Karnes 
in this area rise 200 feet above the surroundings 
in places and are quite extensive. This pit is the 
best exposure at the present time. Sediments show 
massive deposition of sands and gravels from stag- 
nant melting ice, and are characterized by normal 
faulting. None, however, show evidence of thrusting 
or other disturbance as far as ice movement is con- 
cerned. To the southeast, south, and southwest, 
along the Missisquoi and Champlain Valleys, Cham- 
plain Sea sediments contain a till; this area shows 
no disturbance however: hence these deposits are 
interpreted as being post-Missisquoi readvance in 
age, probably related to stagnation of the ice of 
the readvance. 



This stop officially concludes the field trip. The route southward 
suggested below, via Vt. Rts. 108 and 15, passes through Enosburg 
Falls, Jef fersonville, and Cambridge. 

The following log incorporates several features of significance a- 
long the return route: 



373 



Mi lea 


ge 




Cum. 




S/S 


93.5 




0.1 



Turn right as you leave the gravel pit, and pro- 
ceed south. 

96.6 3.1 Intersection with Vt. Rt. 105. Turn right onto 
Rt. 105 (W) . 

97.1 0.5 Enosburg Falls, elevation 422 ft. resting on Cham- 
plain Sea deltaic sediments. 

97.4 0.3 Intersection where Rt. 105 bears right (W) , and 
Rt. 108 continues straight ahead (S). Proceed 
straight ahead. 

100.0 2.6 West Enosburg; From here on, for the next 4 miles, 

the valley of Tyler Branch and The Branch contains 
at least 6 levels (see Figure 3, points 4, 5, 24, 
46-49), from the upper lacustrine ("Coveville" ) to 
the Champlain Sea. These are clearly visible as 
you drive along the length of the valley ahead. 

104.7 4.7 Browns Pond. Above you to the left is a kame ter- 
race which extends southward, merging into the Bak- 
ersfield delta at 740', later reworked to 600' dur- 
ing "Ft. Ann." 

106.7 2.0 Bakersfiald. The town is built upon the 740' sur- 
face. 

107.5 0.8 On southern side of valley, if you turn and look 

back to the right (NW) you can see the 600 foot 
surface in deltaic deposits south of Bakersfield. 
ENTER MT. MANSFIELD 15' Quadrangle. 

110.7 3.2 Off to right, in the floor of the valley with a 

small farm resting on it, is a small moraine con- 
taining cobbles and Champlain Sea sediment, and 
which may mark the southern limit of the readvance; 
here a minor lobe extended down the Missisquoi Black 
Creek Valley from the northwest. 

112.7 2.0 You are now in the Black Creek Valley, which was a 

channel southward at one time for glaciof luvial 
waters; the glaciof luvial sediments are mantled 
first, by lacustrine sediments, and then by Cham- 
plain Sea sediments. 

118.0 5.3 Intersection with Vt. Rt. 109; bear right, staying 

on Rt. 108. 

119.5 1.5 Intersection with Vt. Rt. 15. Turn right (W) , 



37^ 



Mileage 
Cum. S/S 

121.9 2.4 

122.9 1.0 



toward Cambridge. 

Cambridge bridge; turn left (S) , across bridge, 
following Rt. 15 into the town of Cambridge. 

Intersection with Vt. Rt. 104. 

2 choices: 

1. Bear left , and follow Rt. 15 through Underhill, 
Essex Center, and Essex Junction to Interstate 
89 and Burlington. 

2. Proceed straight ahead along Rt. 104 to Fair- 
fax, and turn left (W) onto 104A, 2 miles be- 
yond toward Milton, along the Lamoille River 
and Arrowhead Mountain Lake; turn right onto 
U.S. Rt. 7 at intersection with Rt. 9, then 
onto 1-89, and south toward Burlington and 
points beyond. 



i 



375 



REFERENCES 



Cannon, W. F. , 1964, The Pleistocene geology of the Enosburg Falls 
Quadrangle, Vermont: A report to the State Geologist. On open 
file at the Vermont Geol. Survey, 13 p. 

Chapman, D. H. , 1937, Late-glacial and postglacial history of the 
Champlain Valley: Am. Jour. Sci., v. 34, p. 89-124. 

Connally, G. G. , 1971, Pleistocene mountain glaciation. Northern 
Vermont: Discussion: Geol. Soc. America Bull., v. 82, p. 1763- 
1766. 

Connally, G. G. , and Sirkin, L. A., 1971, Luzerne readvance near 
Glens Falls, New York: Geol. Soc. America Bull., v. 82, p. 9 89- 
1008. 

Gadd, N. R. , 1964, Moraines in the Appalachian region of Quebec: 
Geol. Soc. America Bull., v. 75, 1249-1254. 

Johnson, P. H. , 1970, The surficial geology and Pleistocene history 
of the Milton Quadrangle, Vermont. Unpublished M. S. thesis. 
University of Vermont. 

McDonald, B. C. , 1968, Deglaciation and differential postglacial 
rebound in the Appalachian region of south-eastern Quebec; 
Jour. Geology, v. 76, p. 664-677. 

McDonald, B. C. , and Shilts, W. W. , 1971, Quaternary stratigraphy 
and events in southeastern Quebec: Geol. Soc. America Bull., 
V. 82, p. 683-698. 

Stewart, D. P., 1961, The glacial geology of Vermont: Vermont 
Geol. Survey Bull., no. 19, 124 p. 

Stewart, D. P., and MacClintock, P., 1964, The Wisconsin strati- 
graphy of northern Vermont: Am. Jour. Sci., v. 262, p. 10 89- 
1097. 

Stewart, D. P., and MacClintock, P., 1969, The surficial and 
Pleistocene history of Vermont: Vermont Geol. Survey Bull., 
no. 31, 2 51 p. 

Stewart, D. P., 1971, Pleistocene mountain glaciation, northern 
Vermont: Discussion: Geol. Soc. America Bull., v. 82, p. 1759- 
1760. 

Wagner, W. P., 1969, The late Pleistocene of the Champlain Valley, 
Vermont: New York State Geol. Assoc. Guidebook, 40th Annual 
Meeting, p. 65-80. 



376 



Wagner, W. P., 1970, Pleistocene mountain glaciation, northern 
Vermont: Geol. Soc. America Bull., v. 81, p. 2465-2470. 

Wagner, W. P., 1971, Pleistocene mountain glaciation, northern 
Vermont: Reply: Geol. Soc. America Bull., v. 82, p. 1761- 
1762. 

Wagner, W. P., 1972, Ice Margins and Water Levels in Northwest- 
ern Vermont: N.E.I.G.C. Guidebook, 1972, Burlington, p. 



377 

Trip G-5 

TILL STUDIES, SHELBURNE VERMONT 

by 

W. Philip Waqner, James D. Morse, and Charles C. Howe 
Department of Geology, University of Vermont 

INTRODUCTION 

In the summary report of the Vermont Geoloqical Survey- 
sponsored surficial geology mapping program, Stewart and Mac- 
Clintock (1969) presented the first comprehensive Laurentide 
stratigraphy for the entire state. Surface tills in three reg- 
ions are differentiated primarily on the basis of till fabric. 
In a streambank exposure near Shelburne village in northwestern 
Vermont their "Burlington till " (northwest fabric) is reported 
overlying "Shelburne ti 11" (northeast fabric) (Figure 1). This 
locality is the subject of this report. The renort emphasizes 
till fabric measurements but other parameters are included: col- 
or, texture, lithology, particle shape, heavy minerals, and striae. J 
The bulk of the data is from the exposure previously studied by " 

Stewart and HacClintock but nearby exposures were also sampled. 

Ac knowl e dgements 

Preliminary till fabric measurements at the Slielburne local- 
ity were made in 1966 by M. W. Hebb and S. J. Minor, and in 1069 
by C. A. Howard, Jr. and W. R. Parrott, all students at the Univ- 
ersity of Vermont. The bulk of the data presented here was col- 
lected in 1969 by the senior author with the assistance of B. P. 
Sargent and R. Switzer, also students at the University. 

TILL COLOR 

The first study of the Shelburne locality was made by Stew- 
art (1961, p. 102) who reported northeast fabric maxima in the 
lower, gray-colored part of the till and northwest maxima in the 
upper, brown-colored part. Although he indicated that till color 
differences do not necessarily have stratigraohic significance, 
color is clearly used as a basis for till differentiation (Stew- 
art, 1961, Figure 2 and p. 102). 

A different interpretation of the till colors at Shelburne 
was presented by Thomas (1964) who believed that the brown color- 
ation is due to oxidation of gray colored till. As evidence, he 
cited the pronounced weathered character of particles in the brown 
unit compared to the gray unit, and similar color variations in 
ponded silt and clay deposits in the area. 



^ 



LAKE 
CHAMPLAIN 




'^ ^^ She/burne 
Bay 



378 
Figure 1. Location of till exposure. 



Winootki 



BURLINGTC 



SOUTH 
BURLINGTON 




Map Location 



SHELBURNE 




rSh«lburn« Falls 



SCALE 



Shelburne Two-till Locality 



1 1 1 1 1 -I— I- 



379 



From our study of the Shelburne exposure the following ob- 
servations can be made about the color difference. Munsell color 
codings of wet samples are 10 YR 2/1 and 10 YR 3/4 for the gray- 
and brown-colored till units respectively, with relatively slight 
intra-unit variations. The contact between the brown and gray 
colors is sharp. Lenses of gray-colored till are surrounded by 
brown-colored till, and brown coloration extends downward along 
joints for several feet into the gray-colored unit. In this and 
numerous other exposures in the region showing similar brown-and 
gray-colored till, the contact between the two units generally ap- 
pears to reflect the slope of the overlying ground surface. These 
aspects indicate to us that the color difference can be better ex- 
plained by weathering, as Thomas suggested, than by multiple gla- 
ciation. Furthermore, our attempts to differentiate the brown- 
and gray-colored tills with a variety of parameters, including 
fabric, have been unsuccessful, thereby lending support to the 
view that multiple glaciation is not the cause of the color differ- 
ence . 

FABRIC 

Stewart (1961, p. 102) reported fabric maxima (based on a 
180 degree, two-dimensional reference system) of N30E and N15W for 
the gray- and brown-colored tills, respectively. Thomas' (1964, 
p. 68-72) fabric study of the same exposure showed N25W and N45W 
maxima for gray and brown units, respectively. He also measured 
fabric at a nearby exposure of gray- and brown-colored till, both 
of which had preferred north-south orientations. In unpiiblished 
fabric studies at the same locality, students from the University 
of Vermont consistently have found northeast maxima in the gray- 
colored till; in the brown-colored till, on the other hand, most 
faQDrics showed bimodal distributions with northeast and northwest 
concentrations of varying relative strengths. 

In the work reported here ten fabric analyses were made at 
the Shelburne locality (Figure 2). Eight of the sites were from 
two vertical trenches excavated to assure undisturbed samples, and 
two sites were at the middle and upper central parts of the expos- 
ure. A hand-held Brunton compass was aligned parallel to long 
axes of elongate particles to measure azimuth and inclination. In 
addition, the orientation of blade-and disk-shaped particles was 
determined by measuring the strike and dip of a plexiglass plate 
oriented parallel to flat particle sides. Thus, only azimuth and 
inclination were measured for rod -shaped particles, only strike 
and dip for disk-shaped particles, but both spatial factors were 
measured for blade-shaped particles. Long axis measurements are 
probably accurate to * 5 degrees, whereas strike-dip data are 
somewhat less accurate. 

The data were originally plotted in the field on Schmidt 
equal-area stereo nets. This showed that most fabric patterns are 
polymodal, thus making statistical reduction difficult. To facil- 



380 



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381 



itate reduction of data, the computer program by Spencer and Cla- 
baugh (196 7) was used. Computer printout for long axis data is 
reproduced in Figure 3, and for pole plots of flat particle data 
in Figure 4. Long axis fabrics vary from sample to sample, but 
most tend to be characterized by azimuth maxima predominantly 
in the northeast and southwest quadrants. Thus, no correlation 
between fabric and color difference is apparent. Figure 3 also 
suggests that the inclinations of long axes are not significantly 
different from horizontal. This has been further established by 
simple statistical analyses. Sample 8 is unique for its predom- 
inant northwest - southeast concentration. Due to its proximity 
to the land surface, it is thought that the till in the vicinity 
of sample 8 might be disturbed by mass movement. 

In Illinois Harrison (1957a) found that flat particles tend- 
ed to dip in the upglacier direction. Krumbein (1939, Figure 3) 
depicted short axis plots (comparable to the flat particle fcibrics 
reported here) arranged in a girdle oriented perpendicular to the 
flow direction. Flat particle fabrics from the Shelburne locality 
vary considerably but there is a suggestion that the strike of 
flat particles tends to parallel long axis trend of elongate par- 
ticles, similar to Krumbein 's findings. Note the similarities 
between strike of flat particles (Figure 4) and trend of elongate 
particles (Figure 3) for samples 2, 4, 7, and 8. Although not 
enough is known about flat particle fabrics, it appears that such 
measurements may lend support to long axis data. 

About 200 feet south of the major exposure is a streambank 
showing gray-and brown-colored till. Three till fabric samples 
from this exposure all have strong northeast-southwest maxima. 

Directly across the stream from the major till bank is a 
small exposure of gray till directly overlying bedrock. Addition- 
al fabric measurements were made by sampling from two vertical 
working faces oriented perpendicularly to each other and from a 
third, horizontal face perpendicular to the other two. Thus, fa- 
brics taken from the same till, but from working faces of differ- 
ent orientations, can be compared. The apparent influence of 
working-face orientation on long axis fabrics is striking (Figure 
5) . Poles to working faces are represented by circles on the fa- 
bric diagrams in Figures 5A and 5B. It is believed that working- 
face orientation can introduce a significant bias in some cases 
due to a tendency to oversample particles projecting at high an- 
gles to the working face. Although conscious efforts were made 
to avoid such a bias, the relative difficulty experienced in ex- 
tracting particles oriented nearly parallel with any working face 
made this impossible. Because the majority of till stones plunge 
at low angles, a horizontal working face might introduce less bias 
than other working faces. If this is the case, then the fabric 
of this cube of till is most likely northwest, as the diagram from 
the horizontal working face indicates. Such a trend is exaggerat- 
ed by the working face oriented N70E. For the N20W working face, 



382 







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385 



on the other hand, it appears that a dominant but artificial 
northeast-southwest maximum is created with a lesser concentra- 
tion in the northwest-southeast quadrants. Such a pattern is 
extremely misleading. Similar findings have been reported by 
Johansson (1968, p. 206), Dreimanis (1959), and Thomas (1964), 
all of whom recognized sampling bias as a significant problem. 
Although some of our fabrics were taken on non-horizontal working 
faces, most were taken on horizontal working faces, which are pro- 
bably less subject to this type of bias. 

To what extent till fabric measurements are reliable is pro- 
blematical, but the dominantly northeast-southwest mode is at 
least internally consistent. It is our view that stratigraphic 
subdivision of the Shelburne exposures is not supported by repro- 
ducible fabric data. 

TEXTURE 

No thorough investigation of till texture was made in this 
study. Thomas (1964, p. 135) reported similar grain size distri- 
butions in both gray- and brown-colored till except that the brown 
till contained 10 percent clay versus 25 percent in the gray till. 
Kodl (1967) studied the -20 to greater than 40 size range and 
found no significant differences between a total of six samples 
of gray- and brown-colored till. In our work, caliper measurements 
of long, intermediate, and short axes were made of all particles 
used in the fabric analysis. Visual inspection of graphs of fre- 
quency of various particle sizes showed that all samples appeared 
similar except that samples 7 and 8 contain a higher proportion 
of particles with large long axes than other samples. 

LITHOLOGY 

Thomas (1964, p. 165) measurements of lithology of the gran- 
ule fraction showed no significant differences between the gray- 
and brown-colored tills. Our work included identification of the 
lithology of particles selected for fedaric analyses. This data 
shows considercible variations in particle lithology percentages 
between samples. However, no trends or patterns are apparent. 

Coarse Fraction Particle Shape : Thomas (1964, p. 76-89) 
compared the shapes of carbonate and shale granules in the two 
tills, concluding that there was no significant difference. The 
coarse fraction ($^,3.30) axial measurements from this study 
were plotted on shape triangles as described by Folk (1964) . It 
should be pointed out that inasmuch as only those particles suit- 
able for fabric measurements were considered, equant grains were 
excluded. Nevertheless, the procedure used was similar in all 
cases so that the approach is at least internally consistent. 
Over 90% of the particles can be circumscribed by 0.2 - 0.5 short: 



386 



long axial ratio values and by 0.1 - 1.0 long-minus intermediate: 
long-minus short axial ratio values. A notable exception to this 
is sample number 8 which includes a larger proportion of compact 
particles than any other sample. It appears that this anomaly 
cannot be explained lithologically and is believed to be a signi- 
ficant, difference between samples. 

Heavy Mineral Analysis : Heavy mineral separations of the 
medium sand-sized fraction were conducted by Caldwell (1969) on 
single samples from each of the brown and grey tills. Using brom- 
oform (sp.gr.-^ 2.85), amounts of 81.4% and 77.2% dolomite were 
counted in the heavy fraction of brown and gray till samples, re- 
spectively. Although the dolomite contents do not appear signifi- 
cantly different, Caldwell noted that dolomite in the brown till 
had a "pinkish-orange" color thought to be due to oxidation of the 
brown till. Removal of the dolomite by iodide-acetone separation 
(sp.gr. ^ 3.0), facilitated identification of the non-dolomite 
fraction, but no pronounced differences between the tills were 
found. Also, no significant differences of magnetic fractions 
were detected. 

Clay Fraction Mineralogy : A preliminary X-ray diffraction 
analysis of the clay fraction was made by Parrott (1968) . Six- 
teen samples spanning the contact between the gray- and brown-col- 
ored tills were taken to determine if any differences between the 
tills could be detected. Parrott found a deficiency of calcite 
near the top of the exposure, and a calcite concentration at slight- 
ly greater depth, both of which he attributed to leaching. Chlor- 
ite generally decreases upward, and muscovite, montmorillonite , 
and an unidentified mixed-layer mineral increase upward. Kaolinite 
content is lowest just above the color contact. Plagioclase is 
highest at the middle of the exposure, near the contact. Parrott 
(1968) concluded that no systematic differences between gray- and 
brown-colored tills could be found on the basis of clay mineral- 
ogy. 

STRIAE 

Glacial striae are well developed on a bedrock surface imme- 
diately south of the main till exposure and adjacent to the site 
where the data for the fabric diagrams shown in Figure 5 were col- 
lected. Two directions of striae are discernable. Over most of 
the outcrop surface only one set of striae are found with a N30W- 
S30E trend. In the most recently exposed part of the bedrock an- 
other set of striae oriented north-south appear. It is difficult 
to determine the relative age of the striae. The significance of 
the striae in relation to the main till exposure is unknown. 

SUI4MARY AND CONCLUSIONS 

Our work on till fabric at the Shelburne - Burlington till 
locality does not support the two till view. Three independent 



387 



investigations of till fabric at the site have produced different 
results. Moreover, we have failed to find evidence of strati- 
graphic difference on the basis of a variety of parameters. Draw- 
ing an analogy from the null hypothesis of statistics, no signifi- 
cant stratigraphic differences at Shelburne can be inferred until 
conclusively proven. We prefer to avoid the usage of the terms 
■'brown till" and "gray till" in deference to adjectival expres- 
sions without stratigraphic overtones, i.e. gray- or brown-color- 
ed till. 

Perhaps the most worthwhile information from this study re- 
lates to the subject of till fabrics in general. The suggested 
bias due to working face orientation indicates that the concepts 
of transverse and longitudinal fabric maxima may not be straight 
forward. For example, a vortical working face oriented nearly 
parallel to the direction of former ice movement might result in 
a tendency to undersample the longitudinal population while over- 
sampling the transverse (refer again to Figure 5) . Whole-till 
sampling techniques, as for example the method of Harrison (1957b) 
may be less misleading than our method of fabric measurement. 



388 



I 



REFERENCES CITED 



Caldwell, K. G. , 1969, Heavy Mineral Analysis of the Burlington 
and Shelburne tills: unpublished manuscript. University of 
Vermont, 15 p. 

Dreimanis, A., 1959, Rapid macroscopic fabric studies in drill- 
cores and hand specimens of till and tillite: Jour, of Sed. 
Petrology, v. 29, p. 459-463. 

Folk, R. L., 1964, Petrology of sedimentary rocks: Hemphill's, 
Austin, Texas, 153 p. 

Harrison, P. W. , 1957a, A clay-till fabric: its character and ori- 
gin: Jour, of Geology, v. 65, p. 275-303. 

, 1957b, New techniques for three-dimensional fabric analy- 



sis of till and englacial debris containing particles from 3 
to 40 mm in size: Jour, of Geology, v. 65, p. 98-105. 

Johansson, H. G., 1968, Striae and fabric analyses in a moraine 
exposure in vKsterbotten , N. Sweden: Gaol. Foreni Stockholm 
F^rhandlingar, v. 90, p. 205-212. 

Kodl , E., 1967, Clay mineralogy, size distribution, and heavy 
mineral analysis of the Burlington and Shelburne tills: un- 
published manuscript. University of Vermont, 10 p. 

Krumbein, W. C, 1939, Preferred orientation of pebbles in sedi- 
mentary deposits: Jour, of Geology, v. 47, p. 673-706. 

Parrott, W. R. , 1968, Differentiation of tills within the Cham- 
plain Valley: Clay Mineralogy as determined by X-ray diffrac- 
tion analysis. Preliminary Report: unpublished manuscript. 
University of Vermont, 10 p. 

Spencer, A. B., and Clabaugh, P. S., 1967, Computer program for 
fabric diagrams: Amer. Jour, of Science, v. 265, p. 166-172. 

Stewart, D. P., 1961, The glacial geology of Vermont: Vermont 
Geol. Surv. , Bull. No. 19, 124 p. 

, and MacClintock, P., 1969, The Surficial Geology and Pleis- 
tocene History of Vermont: Vermont Geol. Surv., Bull. No. 31, 
251 p. 

Thomas, H. F., 1964, Late-glacial sedimentation near Burlington, 
Vermont: Ph.D. dissertation. University of Missouri, 212 p. 



389 



Trip G-6 

WOODFORDIAN GLACIAL HISTORY OF THE CHAMPLAIN LOWLAND, 
BURLINGTON TO BRANDON, VERMONT 

by 

G. Gordon Connally and Parker E. Calkin 
State University of New York at Buffalo 

INTRODUCTION 

The surficial geology of the Champlain lowland and bordering 
Green Mountains of west-central Vermont has been generally known 
for many years. However, the results of a recent, comprehensive, 
state-wide study in Vermont and studies in the upper Hudson Valley 
of New York have led to the definition of one major problem and 
the reinterpretation of two significant aspects of deglaciation; 
the physical characteristics of the waning glacier and the extent 
of proglacial lakes impounded by the retreating ice margin. 

At least two tills are present in the Champlain Valley in 
western Vermont and one in the Connecticut Valley in eastern Ver- 
mont. The problem is whether the eastern till correlates with the 
upper or the lower Champlain Valley till. 

The many kame terraces which flank the Green Mountain front 
throughout the Champlain Valley were incorrectly correlated by ear- 
ly workers. This led to the conclusion that the last glacier had 
stagnated and downwasted in place. However, it has now been shown 
that each kame terrace belongs to a discrete south-sloping sequence 
of ice-contact and outwash deposits. The sequences formed succes- 
sively during recession of the margin of a still-active glacier. 

Early workers correctly concluded that the clays, sands, bea- 
ches, and deltas flanking the Green Mountains were results of pro- 
glacial lakes. They inferred that these lakes were confined to 
the Champlain Valley. It has now been shown that the highest lev- 
els in the Champlain Valley were coextensive with similar lakes in 
the Hudson Valley which has led to an updating of terminology. 

ACKNOWLEDGEMENTS 

Field study by Calkin (Middlebury Quad.) and by Connally 
(Brandon and Ticonderoga Quads.) was supported by the Vermont Geol- 
ogical Survey. We are indebted to Dr. Charles G. Doll, State Geol- 
ogist for his help, and to Dr. David P. Stewart of Miami University 
for many stimulating discussions and introduction to the field areas, 



Fig. 1. Generalized glacial geologic 
map of the Champlaln Lowland from 
Burlington to Brandon, Vermont. 

EXPLANATION 



y ^ 



cP 



Bedrock or thin drift 

Till 

Kame terrace 
Esker 

Lacustrine silt and clay 

Lacustrine beach gravel 
of delta gravel 

Marine sand 

Marine beach gravel 




SCALE 



391 



THE BURLINGTON-SHELBURNE PROBLEM 

The Champlain lowland and bordering Green Mountains have 
been overridden at least twice and probably three or more times 
by continental ice sheets during the Pleistocene. McDonald and 
Shilts (1971) record at least three distinct glaciations in Que- 
bec, to the north, while Borns and Calkin (1970) distinguish at 
least two in northwestern Maine, to the east. Local evidence in- 
cludes multiple-till sections, differences in till fabric orien- 
tations, and striations on scoured bedroc)c surfaces, all reported 
by Stewart and MacClintock (1969). 

In four well exposed, multiple-till sections (Shelburne, 
Lewis Creek, Little Creek and West Bridport sites (see stops 1, 3 
and 7, Figure 1) between Burlington and Brandon, lodgement tills 
with northwest fabrics are underlain by similarly compact tills 
with slightly different lithologies and northeast fabrics. At the 
Lewis Creek and Little Otter Creek sites varved clay records an 
ice recession between deposition of the contrasting tills. The 
observations of a northwest-derived surface till over a northeast- 
derived till is supported at several places in the Middlebury, 
Brandon, and Ticonderoga quadrangles where weak but definite north- 
east striae are cut by northwest striae. Supporting evidence from 
fabrics and striae is reported by Stewart and MacClintock (1969) 
for the bordering mountainous areas of northwestern Vermont . Al- 
though the division unfortunately has been based almost entirely 
on till fabrics, and there are occurrences of apparently contra- 
dictory till fabrics; the evidence for two till sheets in west- 
central Vermont is convincing. 

Stewart and MacClintock (1969) defined the lower, northeast- 
derived till as the Shelburne till and the upper, northwest-de- 
rived till as the Burlington till. Some workers have questioned 
the interpretation of two tills at the type section of the Shel- 
burne till, but a more important Burlington-Shelburne problem, 
discussed by Stewart and MacClintock (1969, p. 190), arises rela- 
tive to the definition of the boundary between these tills and the 
correlation of the lower, northeast-derived lodgement till of the 
Champlain Valley with an ciblation till with northeast fabric in 
eastern Vermont. The sandy ablation deposits of southeastern Ver- 
mont may well be the result of normal reorganization and lobation 
of a thinning ice mass in the north-northeast-trending Connecticut 
Valley; therefore, these could have been laid down by the same con- 
tinental glacier that deposited the Burlington till in northwestern 
Vermont as suggested by Shilts and Behling (1967) and postulated by 
Stewart and MacClintock (1969, p. 80) as their Alternate Hypothesis 
III. 

However, the Burlington-Shelburne problem is resolved, the 
Burlington appears to be a lithologically correlatable till sheet 
in northwestern Vermont. The Burlington till may represent the late 



392 



Woodfordian Luzerne readvance; the underlying Shelburne till de- 
posited by the ice sheet that receded from the main Woodfordian 
Ronkonkoma Moraine on Long Island about 18,000 yrs, B. P. (Connal- 
ly and Sirkin, 1972). Alternately, the Burlington drift may be a 
western facies of a much more extensive drift sheet that represents 
the entire Woodfordian. In either case it is possible that at 
least some of the lower tills of multiple till sites in the Cham- 
plain Valley record pre-Woodfordian glaciation. However, Connally 
(1970) postulated that both lodgement tills at the West Bridport 
section are from the last Woodfordian glaciation because of the 
orientation of striae on the smoothly polished bedrock surface be- 
neath the till. 

ACTIVE ICE RETREAT 

Recession from the Burlington glaciation involved stagnation 
and downwasting in the Green Mountains while backwasting of an ac- 
tive, calving, ice margin occurred in the Champlain lowland where 
the terminus fronted a series of expanding glacial lakes. The 
wide, and apparently continuous series of kame terraces depicted 
in Figure 1 can be separated into discrete sequences. Each se- 
quence grades southward from ice-contact deposits, through kame mor- 
aines, and onto outwash aprons. Connally (1970) describes five sep- 
arate sequences in the Brandon quadrangle, each of which includes 
one or more kame terraces. Elsewhere, the presence of interbedded 
tills and lacustrine deposits in numerous subsurface exposures in- 
dicates that the recession of the Burlington glacier involved fre- 
quent frontal oscillations (Calkin, 1965). 

Calkin (196 5) demonstrated that large remnants of stagnant 
ice downwasted in depressions in the Green Mountains producing an 
abundance and variety of dead-ice deposits while continental ice 
was still actively receding in the Champlain Valley, These upland 
remnants shed outwash down the major valleys from high mountain di- 
vides and onto the retreating ice sheet. The outwash forms the 
bulk of the ice-contact drift in many of the kame terraces adjacent 
to the Green Mountains. 

Connally and Sirkin (1970) suggest that the Burlington drift 
of Vermont is equivalent to the till of the Luzerne readvance near 
Glens Falls, New York and is therefore about 13,200 years old. 
Recession from the Luzerne readvance was underway by 13,150 yrs. 
B.P. The ice sheet retreated steadily northward through the Cham- 
plain Valley interrupted only by the Bridport readvance (Connally, 
1970). This readvance extended from the vicinity of Burlington to 
near Bridport about 12,800 yrs. B.P. (Connally and Sirkin, 1972), 
No moraine marks the terminus of this readvance; glacial lake wat- 
ers apparently prevented formation of any distinct recessional mor- 
aines in the lowland. Overriding of lacustrine deposits and calv- 
ing of the active ice margin of the Bridport readvance prob2dDly 
caused the ubiquitous bouldery clay shown by Stewart and MacClin- 
tock (19 70) between Burlington and Bridport. 



393 



GLACIAL LAKE HISTORY 

Chapman (1937, 1942) made an exhaustive study of lacustrine 
and marine strandlines in the Chaunplain Valley. Chapman combined 
the marine levels as The Champlain Sea. He defined an upper, 
Coveville Stage and a lower. Fort Ann Stage comprising Lake Ver- 
mont. Stewart (1961) added an even higher Quaker Springs Stage. 
LaFleur (1965) working in the Hudson Valley, suggested that the 
lowest levels of Lake Albany in the Hudson Valley were coextensive 
with the upper levels of Lake Vermont in the Champlain Valley. 
Connally (1968) working in the uplands between the Hudson and Cham- 
plain Valleys confirmed LaFleur' s suggestion. Connally and Sirkin 
(19 71) altered existing terminology by restricting the name Lake 
Albany to the highest lake in the Hudson Valley, dropping the pro- 
vincial name Lake Vermont, extending the names Ladce Quaker Springs 
and Lake Coveville to the coextensive lakes, and using the name 
Lake Fort Ann for the lowest freshwater lake in the Champlain Val- 
ley. Lakes Albany, Quaker Springs, and probably Coveville extend- 
ed all the way south to the Harbor Hill Moraine across Staten Is- 
land, New York. 

The Woodfordian glacier, in its northward recession up the 
Hudson Valley, fronted an expanding Lake Albany. The Luzerne re- 
advance took place during the existence of this lake and presumably 
the deposition of the Burlington till. With retreat of the Burl- 
ington ice margin into the Champlain Valley, the land to the south 
rebounded differentially causing a relative lowering of the lake 
level amd formation of Lake Quaker Springs. Stewart and MacClin- 
tock (1969, 1970) projected Lake QucUcer Springs northward to the 
Lamoille River, 15 miles north of Burlington, They state (1969, 
p. 163) that in this general area "the shore line features are so 
well developed that they seem to indicate that the Quaker Springs 
Lake was in existence for an interval as long as the later lake 
stages". However, good evidence for this lake is lacking north of 
Brandon in the Brandon and Middlebury quadrangles and Connally and 
Sirkin (1972) and Connally (1972) place the ice margin in the vic- 
inity of Brandon, amd Ticonderoga, New York, during Lake QuaUcer 
Springs. 

As the ice margin retreated northward the land continued to 
rebound amd the outlet shared by Lakes Albany and Quaker Springs 
was evidently breached forming Lake Coveville at a lower elevation. 
The ice retreated to near Burlington, readvanced to Bridport, and 
then retreated at least as far as the Lamoille Valley; all during 
the existence of Lake Coveville. Finally, the ice retreated to 
the north end of the Chaunplain Valley, the land continued to re- 
bound, and a probadale dam near Fort Ann, New York, formed Lake Fort 
Ann. Lake Fort Ann was most likely dammed to the north by the gla- 
cier as it stood at the Highland Front Moraine about 12,600 yrs. 
B.P. 



39^ 



Retreat of the Burlington ice north of the St. Lawrence Val- 
ley allowed Laike Fort Ann to drain northward down to lower levels 
(see Wagner, 1969). Following a short erosional interval (Stew- 
art and MacClintock, 1969, p. 178) the Champlain Valley was invad- 
ed by marine waters to form the Champlain Sea. Coldwater marine 
molluscs in clays and sands between Vergennes and Burlington doc- 
ument at least one stage of the Champlain Sea in the field trip 
area. 

FIELD TRIP STOP DESCRIPTIONS 

Topographic 15 minute quadrangles covered: Burlington 

Middlebury 
Ticonderoga 
Brandon 

STOP 1. SHELBURNE VILLAGE SECTION: This is the type locality for 
the Shelburne drift described by Stewart (1961, p. 102) as "a small 
stream valley, one and one-quarter miles south-southwest of Shel- 
burne Village. The Valley walls ... expose a layer of dark gray 
till over bedrock ... overlain by fifteen feet of red-brown sandy 
till that is covered by four to eight feet of bouldery lacustrine 
clay. ... The orientation of pebbles in the gray till show a fabric 
with maximum approximately north 30° east. The fabric of the over- 
lying till is north 15° west." The lower till was later named the 
Shelburne till. Many workers have subsequently visited this sec- 
tion; some have supported the two-till interpretation while others 
have challenged it. 

STOP 2. LEWIS CREEK DELTA: A gully exposure in this marine delta, 
1500' south of Lewis Creek off Rt. 7 displayed the following sect- 
ion in 1965: 

2' Sand, pebbly, probably marine; at 200' elevation, 

15' Clay, gray, with scattered shells of marine clams. 

8' Clay, brown, bouldery, probably lacustrine. 

5' Till, gray lodgement; boulder pavement at top. 

1' Sand, brown, stratified. 

A very well formed beach ridge nearby at 250' may mark the high 
stage of the Chcimplain Sea or a post Lake Fort Ann stage, called 
"Lake New York" by Wagner (1969). 

STOP 3. LITTLE OTTER CREEK SECTION: The composite section along 
the creek two miles north of New Haven shows the following: 

2-10' Clay, bouldery, with stratified lenses of silt 
and sand; lateral gradation to till. 



395 



3-10' Till, clay-rich with boulders of varved clay; 
fabrics are N 4"*W, N S'W, and N BS^W. 

3' Varved clay in situ. 

14' Till, brown, bouldery, lodgement; fabrics are 
N 35° E and N 19° E. 

15' Sand, pebbly, poorly stratified and interbedded 
till. 

The upper till may be assigned to the Burlington Stade, the lower 
to the Shelburne (Calkin, 1965). Interbedded tills and lacustrine 
deposits suggest an active oscillating ice margin. 

STOP 4. BRISTOL KAME TERRACE - DELTA: The ice contact deposits 
as first described by Chapman (1942) appear to be topped by a del- 
taic surface (village and airport) of Lake Coveville at 570*. 
Wave erosion at this level may have carried gravel out over the 
ice contact gravels to form the foreset-like beds seen at the out- 
er edge (Stewart and MacClintock, 1969). Weak bars at the Lake 
Fort Ann level (420' here) occur nearby. 

STOP 5. THE COBBLE AND KETTLED KAME TERRACE: Five miles south 
of Bristol off Rt. 116 is the Cobble, a bedrock outliner which 
has controlled the great width of the kame terrace here. Two ket- 
tle holes over 40' deep in the surface at 540-580' are below the 
level projected for Lake Quaker Springs. Do these kettles pre- 
clude the existence of Lake Quaker Springs here ? 

STOP 6. CHIPMAN HILL, MIDDLEBURY AND LUNCH. This hill has more 
than 400' of relief, has exposures of bedrock near the base at the 
north, but only till is found at the surface within the upper 300', 
Is it a drumlin ? 

STOP 7. WEST BRIDPORT SECTION: This section was described by 
Connally (1970, p. 11). In 1964 the exposure showed: 

0-2' Silty-clay containing ice-rafted (?) pebbles and 
boulders. 

16' Silt and sand, laminated to thin-bedded, lacustrine. 

5 1/2' Clay-loam till, dark gray (N3) , with a lower 12-18" 
gray-black (N2) till overlain by 12-18" of oxidized 
gravel at the base. 

3' Sandy-loam till, light olive-gray (5y 5/2), cal- 
careous sandy- loam till. 

Bedrock with striae oriented N 10° E. 



396 



Till fabric maxima are N 50" E for the olive-gray till and N 30" 
W for the overlying dark gray till. This agrees with the defini- 
tion of NE Shelburne overlain by NW Burlington as seen at Stop 1, 
However, Connally (1970, Table 2) attributes the striae and both 
tills to the Burlington advance. The upper, bouldery, silty-clay 
is inferred to represent the Bridport readvance. 

STOP 8. BRANDON- FORESTDALE DELTA: This delta was deposited by 
the Neshobe River. Chapman (19 37, p. 59) inferred the Coveville 
level at 430* at Brandon but Connally (1970, p. 21) placed it at 
405' farther south where Chapman's projection is 420', Chapman 
attributed higher levels to local lakes but Connally correlated 
the well developed 500' level with Lake Quaker Springs. If time 
permits the 405', 500', and a higher 565' level related to the Lake 
Dunmore kame moraine will be visited. 

STOP 9. LAKE DUNMORE KAME MORAINE: The kame moraine is part of a 
full deglacial sequence that consists of kame terraces surrounding 
Lake Dunmore, the moraine, outwash at Forestdale, and the eastern 
channel of the Brandon-Forestdale delta that is graded to a local 
lake level at 565*. We will drive through this sequence and stop 
if time permits. 

STOP 10. COVEVILLE BEACH: Reworking of a kame terrace belonging 
to a sequence higher and earlier than the LeUce Dunmore moraine is 
present north of the Middlebury River. This kcune terrace has been 
reworked to form a sandy apron, probably a beach, at the base of 
the terrace at 480'. This is only about 20* below Chapman's pro- 
jection for Lake Coveville. Because there is no beach between the 
pre-Lake Quaker Springs kame terrace and the Coveville level beach, 
the northern boundary of Lake Quaker Springs is inferred to be 
south of the Middlebury River, near Brandon. 



REFERENCES CITED 

Boms, H. W. , and Calkin, P. E. , 1970, Quaternary history of north- 
western Maine; in Boone, G. M. (Editor), Guidebook, N.E.I.G.C., 
62nd Ann. Mtg. , p. E-2, 1-6, 

Calkin, P. E. , 1965, Glacial Geology of the Middlebury fifteen min- 
ute quadrangle; Open- file Rept. to Vermont State Geologist, 
23 p. 

Chapman, D. E. , 1937, Late-glacial and post-glacial history of the 
Champlain Valley: American Jour, of Sci., v. 34, p. 89-124. 

, 1942, Late-glacial and post-glacial history of the Champlain 



Valley, Vermont: Vermont State Geologist, 23rd Rept., p. 48-83, 

Connally, G. G. , 1968, Surficial resources of the Champlain Basin: 
Ms. to New York State Office of Planning Coordination, 111 p. 



I 



397 



, 1970, Surficial geology of the Brandon-Ticonderoga 15-min- 

ute quadrangles, Vermont: Vermont Geol. Survey, Studies in Vt. 
Geol. , No. 2, 32 p. 

, 1972, Major proglacial laOces in the Hudson Valley and their 

rebound history (Abs.): Geol. Soc. America, Abstracts with Pro- 
grams, Pt. 1, p. 11. 

, and Sirkin, L. A,, 1970, Late glacial history of the upper 



Wallkill Valley, New York: Geol. Soc. America Bull., v. 81, 
p. 3797-3306. 

, and , 1971, The Luzerne readvance near Glens Falls, 

New York: Geol. Soc. America Bull., v. 82, p. 989-1008. 

, and , 1972, The Wisconsinan history of the Hudson- 
Champ lain~ToFe: Geol. Soc. America, Spec. Paper (in press). 

LaFleur, R. G. , 1965, Glacial geology of the Troy, New York quad- 
rangle: New York State Museum, Map and Chart Series 7, 22 p. 

MacDonald, B. C, , and Shilts, W. W. , 1971, Quaternary stratigraphy 
and events in southeastern Quebec: Geol. Soc. America Bull., 
V. 82, p. 683-698. 

Shilts, W. W. , and Behling, R. E. , 1967, Deglaciation of the Ver- 
mont Valley and adjacent highlands (Abs.): Geol. Soc. America, 
Abstracts Ann. Mtg. , p. 203. 

Stewart, D. P., 1961, Glacial history of Vermont: Vermont Geol. 
Survey Bull., No. 31, 124 p. 

, and MacClintock, P., 1964, The Wisconsin stratigraphy of 

northern Vermont: American Jour. Sci., v. 262, p. 1089-1097. 

, and , 1969, The surficial geology and Pleistocene 

HTstory of Vermont: Vermont Geol. Survey Bull., No. 31, 
251 p. 

, and , 1970, Surficial geologic map of Vermont: Doll, 

C. G. (Editor) , Vermont Geol. Survey. 



Wagner, W. P., 1969, The late Pleistocene of the Champlain Valley, 
Vermont: in Barnett, S. G. (Editor) Guidebook, New York State 
Geol. Assoc, 40th Ann. Mtg., p. 65-80, 



400 



Lake Studies Cover page; Various aspects of Lake Studies program, 
UVM Department of Geology. Photo at lower left by Robert Howe, 
UVM Geology Department, All others by Arthur Huse. 



ifOi 



Trip IS-1 

THE SLUDGE BED AT FORT TICONDEROGA, NEW YORK 

D. W. Folger 
Middlebury College, Middlebury, Vermont 

Introduction 

While the legal battle has raged between Vermont and New 
York over the future of the sludge bed located at the mouth of 
Ticonderoga Creek, southern Lake Champlain, several comprehensive 
studies have been underway to determine the size, shape, and 
composition of the organic-rich deposit and its effect on lake 
geology, chemistry, and biology. Those involved represent Federal, 
State, and private organizations. Among them are the Federal Water 
Quality Administration', the U.S. Army Corps of Engineers, the 
University of Vermont and Middlebury College (FWPCA, 19 6 8; 
FWQA, 1970, Folger, 1972). 

Participants in this field trip will study the area (Fig. 1) 
from Middlebury College's research craft with such equipment as 
an echo sounder, surface drifters. Van Dorn bottles, secchi disc, 
dissolved oxygen kit, and grab samplers. They will thus gain a 
first hand look at the bathymetry, current regime, suspended matter 
and oxygen distribution and will be able to assess the effect of 
the pollutants on some physical properties of the sediments. 

Creek Inflow and Sediment Characteristics 

Ticonderoga Creek flows eastward from Lake George through 
the village of Ticonderoga to Lake Champlain over a distance of 
5 km and vertical drop of 7 4 meters. Creek discharge at Lake 



402 



73'24*>/ 




Hf- defiance. 



:;• 43 $o*/ 



Figure 1. Contours showing organic carbon concentration 
(% dry weight) in bottom sediments of Lake 
Champlain. 



kOJ 



George averaged 9 m^/sec over a 17 year period with a maximum 
daily flow of 37 m'/sec and minimum of about 0.2 m^/sec (Wells, 
1960). Because of five dams on the creek and because the creek 
and its main tributary, Trout Brook, both flow mostly over 
resistant metamorphic terrane where gradients are steepest the 
natural suspended load transported to Lake Champlain is probably 
low except during periods of high runoff. Below the dams, however, 
the creek carried abundant waste to the lake from the International 
Paper Company plant while it was in operation. Much of the delta 
built into the lake therefore consists of material derived from 
the paper plant and other industrial or municipal sources (FWQA, 
1970). 

The lake bottom drops off from the shallow delta front to 
the axis of the main lake channel where maximum depths are between 
6 and 7 meters. The dark gray to black silty, sandy clays that 
cover the bottom near the creek mouth grade to very fine-grained 
greenish-gray clay (median diameter < 2 microns) over a distance 
of several kilometers to the north and south. Acoustic penetration 
at 50 kHz of several meters in the finest textured clay is sharply 
reduced in sediments near the creek mouth. This is probably due 
to the coarser texture of the material but it may be due partly 
to the abundant gas in the most organic-rich sediments. Chlorite 
and illite are the dominant constituents of most bottom sediments 
in the southern part of the lake. Near Ticonderoga Creek, however, 
kaolinite becomes abundant with pollutants such as wood chips and 
fibers (Aubrey, 1971). 



kok 



Pollutant Distribution 

Because organic carbon is abundant in the paper plant 
waste, its distribution can be used to outline the sludge bed. 
Figure 1 shows contours of the organic carbon in bottom sediments. 
Highest values (^^-14%) are concentrated near the creek mouth and 
decline to the north and south where few values exceed 2%. Some 
higher values have been measured in sub-bottom sediments (FWQA, 
1970). Nitrogen is distributed in a similar pattern but concentrations 
grade only from about 0.4% to 0.2%. The highest values probably 
result mostly from raw sewage dumped into Ticonderoga Creek by the 
village of Ticonderoga (FWQA, 1970). Measurements of titanium, 
which is used as a whitener in the paper making process, have been 
made on sub-bottom samples collected on or near the delta. Con- 
centrations range from 14. 7% to less than 1% (FWQA, 1970). All 
three components decline in concentrations with distance from the 
creek mouth and appear to be good indices of effluent distribution 
on the bottom. 

Flow Regime and Suspended Matter 

The distribution of carbon also provides a rough guide to 
the flow regime of the lake in the area. Highest values, for 
example , extend farther north than south apparently as a result of 
the predominant northward flow of the lake. The smaller tongue of 
high values that extends southward probably is caused by the 
physiography of the delta which directs some creek flow southward 
especially on the west side of the lake and by reversals of lake 
flow when strong winds periodically blow from the north. Measurements 



^05 



of surface currents in the fall of 1971 verified motion in both 
directions. Four surface drifters released in mid-channel north of 
Buoy 39 Marina moved northward at velocities between 6 and 12 cm/sec; 
two others released off the Marina moved southward at velocities 
between 1 and 5 cm/sec. Flow over the sludge bed is apparently 
sufficient to prevent oxygen depletion in bottom waters. 

The concentration of suspended matter in bottom waters during 
the fall of 1970 ranged from about 15 to 20 mg/liter. Because 
higher values ('^^2 5 mg/liter) were observed north of the area shown 
in Fig. 1, it is doubtful that pollutants from the creek are 
primarily responsible for the high turbidity. Rather, most 
suspended matter probably consists of clay minerals stirred up 
by waves from the broad shallow shelf that surrounds most of the 
southern part of the lake. 



^06 



Aubrey, W. A., 1971, A general survey of the surficial bottom 

sediments between Larabees Point and Chipman Point in the 
Lake Champlain Basin. Unpublished undergraduate thesis, 
Middlebury College, 48 p. 

Federal Water Pollution Control Administration, 196 8, Pollution 
of Interstate Waters of Lake Champlain and its tributary 
basin-New York-Vermont; Proceedings of the first session 
conference. U.S. Dept. Interior, FWPCA, U-16 p. 

Federal Water Quality Administration, 1970, Pollution of the 
Interstate waters of Lake Champlain and its tributary 
basin-New York-Vermont; Proceedings of the second session 
conference. U.S. Dept. Interior, FWQA, 334 p. 

Folger, D. W. , 1972, Distribution of some pollutants in southern 
Lake Champlain, Vermont and New York, (abst) Geol. Soc. 
America v. 4(1), p. 16. 

Wells, J. B. B. , 1960, Surface Water Supply papers of the United 
States, 1959 - part 4, St. Lawrence River Basin. U.S. Geol, 
Survey, WSP 1627, p. 371. 



407 



Trips 12-2, 12-3 
SEDIMENTOLOGICAL AND LIMNOLOGICAL STUDIES OF LAKE CHAMPLAIN 

by 

A. S. Hunt, E. B. Henson, D. P. Bucke 
Departments of Geology and Zoology 
University of Vermont 

INTRODUCTION 

Lake Champlain, one of the largest lakes in the United 
States, represents a major water resource for the northeast as 
well as a source of recreation, transportation, and municipal 
water. Before 1965, very few data were available on the lake. 
In that year, a cooperative study was undertaken by workers in 
several departments at the University of Vermont including bio- 
chemistry, botany, engineering, geology, and zoology, to gain a 
better understanding of the lake's past history, present condi- 
tion, and future prospects. The purpose of this trip is to dem- 
onstrate the type of research being done, and report some of the 
findings. 

We would like to thank Drs . Milton Potash and Philip W. 
Cook for contributing data on general limnology and phytoplank- 
ton, and Richard Furbush, Master of the UVM Melosira , for many 
successful cruises. Without the help of our graduate students, 
who have been credited where appropriate, this report would not 
have been possible. The work upon which this research was based 
was supported in part by funds provided by the U. S. Department 
of Interior as authorized under the Water Resources Research Act 
of 1964, Public Law 88-379. 

Present Lake Champlain 

Lake Champlain is approximately 110 miles long and has a 
maximum width of twelve miles, measured from the Little Ausable 
River, New York, to the shore of Malletts Bay, Vermont. It has a 
mean elevation of 92.5 feet above sea level and a water surface of 
437 square miles (gross area 490 square miles) . As discussed else- 
where (Hunt, Boardman, and Stein, 1971) Lake Champlain is composed 
of two morphologically distinct although interconnected north-south 
trending water bodies. The larger body is referred to as the main 
lake. The smaller water mass to the east, called the east limb, 
is connected with the main lake by three narrow passages. The low- 
er third of the lake resembles a river in that its maximum width 
is one mile and its maximum depth 20 feet. The south end of the 
lake is connected with the Hudson River via locks of the Champlain 
Barge Canal. North of Crown Point, New York, the basin widens and 
deepens reaching a maximum depth of 400 feet near Split Rock Point. 



408 



74*00' 



75*00' 



71*00' 



45*00'-- 




4i^00' - 



EXPLANATION 

7") 



Green Mountains 



Adirondack Mountains 



U.l;..I.-.". ...■.-. -J 



Vermont Valley 



Channplain - St. Lawrence 
Lowlands 



] 



laconic Mountains 



45*00 



Figure 1. Morphological Regions of the Champlain Drainage Basin. 
The dashed lines designate drainage sub-basins. (From 
Hunt, Townsend, and Boardman, 1968). 



Huy 



1^ 



Figure 2. The Lake Cheunplain Drainage Basin. (From Hunt, Townsend, 
and Boardman, 1968) . 




ir 



ICAll t'tDO.OOO 



UMTIO ITATIt tlOLO«ICAk lURVIT. It*«, ■«< 

CMAOlAM MPMTMNT MIIIII AM TCCHMICAL •UIVITI. pftt 



iflO 



From Split Rock Point northward the lake becomes broader reach- 
ing its maximum width north of Burlington. Still further north 
it again takes on the character of a river, as it flows northward 
over a bedrock sill through the Richelieu to the St. Lawrence Riv- 
er. The mean discharge at Chambly, Quebec, is 10,900 cfs. 

The drainage basin can be divided into five morphological 
regions (Figure 1). These include the Green Mountains, Adiron- 
dack Mountains, Vermont Valley, Champlain-St . Lawrence Lowlands, 
and the Taconic Mountains. 

Fifteen hydrologic regions of the drainage basin have been 
delineated such that all of the tributaries in any region drain 
into a specified portion of the lake (Figure 2) . This allows for 
an interrelated study between the drainage areas and the mineral 
budgets of the lake, a long-term study that is now in progress. 

An inventory has been made of all of the streams that drain 
directly into the lake. Of a total of 296, only 34 have water- 
sheds in excess of 10 square miles. In fact, 10 streams drain 
80% of the total Champlain basin, and the 24 largest streams 
drain 95% of the total basin. There are 12 streams with drainage 
basins larger than 100 sq. miles; the largest is the Winooski wat- 
ershed (1,092 sq. mi.). These streams discharge an average of 
approximately 12,000 cfs. of water into the lake. The volume of 
the lake is 912 x 10^ cubic feet (Hunt, Boardman, and Stein, 1971), 
resulting in an average refilling rate of approximately 3 years. 
Some additional hydrological information has been summarized in 
figure 3 . 



West Side East Side Total Basin 



Catchment area: 

Percent of total area: 

Mean discharge/sq.mile: 

Calculated total discharge 
into lake: 

Percent of discharge into 
lake : 



2,618 

33.8 

1.327 

3,474 

29 



5,126 7,744 sq.mi. 

66.2 100 

1.639 1.523 cfs/sq, 

mi, 

8,402 11,876 cfs 



71 



100 



Figure 3. Provisional Summarized Hydrological Data for Lake 
Champlain. 

The bedrock geology surrounding the lake basin consists of 
a diverse assemblage of rocks (Figure 4) . High grade metamorphic 



•f-XX 



rocks of the Adirondack Mountains, mantled by unmetamorphosed 
sandstones and carbonate rocks, border the western margin of the 
lake. Unmetamorphosed or low grade metamorphosed carbonates, 
sandstones, and shales border the eastern margin and presumably 
underlie a large portion of the lake proper. 

GEOLOGICAL HISTORY 

The recorded geologic history of the Champlain basin start- 
ed in the lower Paleozoic when sediments were deposited in marine 
waters that invaded eastern North America. These sedimentary rocks, 
which consist of limestones, shales, and sandstones, form the pre- 
sent lake basin. Thrusting from the east during the Paleozoic 
brought more highly metamorphosed rocks, which define the eastern 
margin of the lake basin, into contact with the relatively undis- 
turbed basin rocks. The elongate shape of the basin, as well as 
the rapid change in the bedrock lithology across the lake, sug- 
gest that faulting may have played a part in basin deepening. 

The history of the lake from the Paleozoic to the Late Pleis- 
tocene is not known, although for at least part of this interval 
the basin may have served as a river valley. 

Evidence for glacial scouring is found today in the lake's 
ungraded longitudinal profile and in basins more than 300 feet 
beneath sea level. Presumably several times during the Pleisto- 
cene, ice occupied the lake basin. To date, however, no Pleisto- 
cene deposits older than Wisconsinan have been identified. Inter- 
pretations of the Icike's Pleistocene history have been based pri- 
marily upon the recognition of former lake levels, some of which 
today are several hundred feet above sea level. The elevated 
shorelines are identified by ancient beaches, wave-cut and wave- 
built terraces, spits, and deltas. Chapman (1937) made a classic 
study of the lake history and a resume of his findings is given 
here. Modifications of Chapman's regional framework include stu- 
dies by Stewart (1961) , and Stewart and MacClintock (1969) . Chap- 
man recognized three water planes. Two of these end abruptly when 
traced northward through the Champlain Valley. The highest plane 
can be traced to Burlington where it is at an elevation of about 
600 feet. The middle plane, which rests about 100 feet beneath 
the highest plane, may be traced to the International Boundary. 
These two higher planes presumably terminate because they formed 
in a water body which abutted against the retreating ice margin. 
The lake in which these upper planes formed has been given the 
name Lake Vermont (Woodworth, 190 5) . During the time when the 
highest plane was formed. Lake Vei^nont drained southward through 
an outlet channel at Coveville, New York. The middle water plane 
(Fort Ann stage) formed at a later time when a new, more northerly 
outlet of lower elevation developed near Fort Ann. After the ice 
lobe had retreated sufficiently, the water level in the Champlain 



^12 



74*00' 



73*00' 




7/1 



EXPLANATION 



- • 45^00' 



metamorphosed medium- (jrade 
s«n(l$ton«s, shales, and volcan- 
ics 



unmefamorpHosed or low-qrade 
mrfamorphic sandstones, carb- 
onates^ and shales 



me+omorphosed qnaywackcs, 
volcamcs, and shales 



00' 



— ■ 4-^*00' 



A5'00' 



1^ v'-> tN-^ 



iqneous and hiqh-<jn3dc meia- 
morphic rocks of +h€ Adir- 
ondack and Green Mountains 

Figure 4. Major Rock Terrains of the Champlain Drainage Basins. 
The dashed lines designate drainage sub-basins. (From 
Hunt, Townsend, and Boardman, 1968) . 



413 



Valley again dropped - this time several hundred feet, until it 
was continuous with marine water in the St. Lawrence lowlands. 
In the estuary which resulted, called the Champlain Sea, the low- 
est shorelines formed. Some time after the marine inundation the 
northern portion of the valley began to rise more rapidly than 
the southern portion. In time, the Richelieu threshold just north 
of the International Boundary was effective in preventing marine 
waters from entering the valley and the existing fresh water lake 
developed. Future tilting of only four-tenths of a foot per mile 
would cause Lake Champlain to again drain southward. This is only 
a small fraction of the tilting which has taken place since the 
Champlain basin was inundated by marine waters. 



WATER PROPERTIES 

Temperature ;- The major portion of Lake Champlain can be 
considered to be a deep cold-water mesotrophic lake. Technically, 
it is classed as a dimictic lake (Hutchinson, 1957) . This means 
that it has two periods during the year when the water in the lake 
is of equal temperature and is mixing. These periods of mixing 
alternate with periods of thermal stratification. 

Thermal stratification begins to develop in June, and is 
well established in July and August. During mid-summer the meta- 
limnion is at a depth of approximately 15 meters and includes the 
12°C - IS'C isotherms. The period of summer stratification is 
short, for the depth of the thermocline increases steadily 
through August and September until the fall overturn takes place 
in October or November. Bottom temperatures in deep water re- 
main at about 6*C during summer, but may rise to 12°C at the on- 
set of the fall overturn. 

The waters in the southern end and in the northeastern re- 
gion of the lake are somewhat warmer than in the main lake, and 
warmer water is found in the bays along both shores. 

During the winter most of the lake freezes over, and in- 
verse thermal stratification develops with 4''C water at the bot- 
tom and 0°C water under the ice. Freezing begins in the narrow 
southern end, in the northern end, and in the northeastern por- 
tion of the lake. The wide main body of the lake is the last to 
freeze. In mild winters this portion may remain open throughout 
the winter season. The duration and intensity of the freeze de- 
pends on the severity of the winter. 

Transparency ;- The transparency of the lake, measured with 
a Secchi disc, ranges from about 3 to 6 meters. The deeper read- 
ings are encountered in late summer when algal growth is less. 
The disc reading in the southern part of the lake is usually less 
than 1 meter. Legge (1969) measured the penetration of light in 



km- 



the lake, using a submarine photometer. Ten percent of incident 
light was usually found at a depth of 3 meters, 5 percent at 5 
meters, and 1 percent at approximately 10 meters. The level of 1 
percent incident light is therefore above the level of the thermo- 
cline. 

pH and Alkalinity ;- Champlain is an alkaline lake. The pH 
of surface water is above 8.0, but in the deep water the pH may 
get as low as 7.3. 

The total alkalinity in the main lake, predominantly as bi- 
carbonate, ranges between 38 and 46 mg/1 , and averages 41 mg/1. 
Alkalinity values are higher in the southern end of the lake, and 
minimal values are found in the water in the northeastern sector. 
Abnormally high values are sometimes encountered at stations close 
to shore, modified by tributary inflow. The alkalinity at Rouses 
Point, near the outlet of the lake, is actually less than that of 
the main lake. 

Major Cations :- The four major cations (Ca, Na, Mg, and K) 
have been measured in the lake and the results are summarized in 
Potash, Sundberg, and Henson (1969a). In the main lake the con- 
centrations of these four cations are ranked in descending order 
as Ca, Na, Mg, and K, with median values of 15.8, 3.9, 3.6, and 
1.1 mg/1. In the southern part the descending rank order is Ca, 
Mg, Na, and K, with median values of 24.4, 5.8, 5.1, and 1.2. In 
flowing from the south to the central lake, the water is diminish- 
ed in the concentration of all four cations, especially in magne- 
sium. The concentrations in the northeastern region of the lake 
are significantly less than in the main lake. In this part of the 
lake the descending rank order is Ca, Na , Mg, and K, the same as 
for the main lake, but the median values are 13.2, 3.0, 2.9, and 
1.3 respectively. It is suspected that these differences between 
the main lake and the northeastern portion of the lake are influ- 
enced, in part, by ground-water intrusion, while the differences 
between the main lake and the southern lake are a result of sur- 
face inflow. 

Major Anions ;- The dominant anion in the lake water is the 
bicarbonate ion, which is mentioned under alkalinity. A few de- 
terminations have been made of the chloride and the sulphate ions. 
In the main lake the median concentration of sulphate is 15.4 
mg/1, and of CI, is 5.7 mg/1. The pattern for these anions is the 
same as for the cations; values are higher in the southern end of 
the lake, and lower in the northeastern part of the lake. 

Dissolved Oxygen ;- The concentration of oxygen dissolved 
in the lake water is one of the more significant parameters mea- 
sured in lakes; it is essential for respiration for all animals 
and most plants, it facilitates the decomposition of organic mat- 
ter in the lake, and it serves as an index for the general quality 
of the lake water. The major sources of oxygen dissolved in the 



-'■^J 



water are from exchange with the atmosphere and from photosynthe- 
sis by the plants in the lake. Oxygen is lost through respira- 
tion, decomposition, and increased temperature. The crucial test 
is the amount of oxygen in the deep water below the thermocline. 
In the deep water there is no source of new oxygen, and the sup- 
ply that is there when stratification begins must last for the 
entire summer until the fall overturn mixes the water and carries 
down a new supply. 

The trophic standard of a lake is sometimes measured by the 
concentration of dissolved oxygen in the deep water. In an oligo- 
trophic lake the amount of organic material in the deep water dur- 
ing the period of summer stratification is of such small magnitude 
that oxygen consumed by decomposition has little effect on the 
concentration of oxygen in deep water. In a eutrophic lake, how- 
ever, decomposition in deep water is great enough to reduce sig- 
nificantly the concentration of oxygen. 

The main body of Lake Champlain is considered oligotrophic 
to mesotrophic by the oxygen standard. The lake water was more 
than 90 percent saturated in April, 1967, after the break-up of 
the ice cover. The oxygen in deep water from August through Oct- 
ober was slightly less than 80 percent of saturation. 

In some sheltered areas of the lake, for example, Malletts 
Bay, deep-water oxygen may be reduced to less than 1 percent of 
saturation (Potash, 1965; Potash and Henson, 1966; Potash, Sund- 
berg, and Henson, 1969b) . These are considered to be eutrophic 
areas of the lake. 

BIOLOGICAL ASPECTS 

Phy toplankton : - The phytoplankton is dominated by diatoms 
and blue-green algae. Asterionella , Diatoma , Melosira , and Frag - 
ilaria are dominant genera during the spring. Ceratium may become 
the dominant organism during mid-summer and the late summer-aut- 
umn plankton is characterized by the abundance of Tabellaria , Gom- 
phosphaeria , and Anabaena . Overall, the phytoplankton is charac- 
teristic of a mesotrophic lake. Muenscher (1930) described the 
algae of the lake for 1928. Sherman (1972) has studied the dia- 
toms in lake cores. 

Zooplankton :- Ten species of Copepods (7 genera) and 12 spe- 
cies (9 genera) of Cladocora have been recorded from the lake. 
Among the Cladocera, Bosmina , D aphnia , and Diaphanosoma were the 
most abundant and widely distributed. Diaptomus and Cyclops were 
the only ubiquitous copepods. Dinobryon was found to oe tne most 
common Protozoa. Legge (1969) has described the seasonal distri- 
bution of the calanoid copepods in the lake. 

Benthos :- The shallow-water (littoral) benthos consist of 
the usual communities of molluscs and insect larvae. The deep- 



416 



water fauna in organic silt consists of small worms, the glacial 
relic shrimp Pontoporeia , small clams, and a larval chironomid- 
ae . 

Relic Pleistocene Fauna :- The fauna of Lake Champlain in- 
clude s~ieverar^pecTei~ that are considered to be relics of the 
Pleistocene. Most of these animals are small invertebrates as- 
sociated with the cold, deeper waters of the lake. They are main- 
ly among the Crustacea. The schizopod species Mysis relicta 
(Opossum shrimp) , a form common to the Atlantic Ocean'ii Is Found. 
Another inhabitant is the amphipod shrimp, Pontoporeia af finis , 
which *ias discovered in this lake only within the last five years. 
Both of these animals are common in the Great Lakes, but apparent- 
ly are not very abundant in Lake Champlain. According to present 
thought these two species were able to inhabit the Pleistocene 
proglacial lakes and migrated from the Baltic Sea area during the 
Pleistocene, using a path around the Arctic Ocean, down through 
the Canadian chain of lakes, through the Great Lakes, to Lake Cham- 
plain (Ricker, 1959; Henson, 1966). Lake Champlain represents a 
terminus for these animals. Pontoporeia has not been found north 
of the St. Lawrence River east of the Ottawa River. Presumably 
an ice block prevented their migration into this area of the con- 
tinent. There are some other animals in the lake which also are 
considered to be glacial relics. Among the small crustacean zoo- 
plankton would be included Senecella calanoides , which was first 
described from one of the Finger Lakes of New York, and Limnocal - 
anus macrurus . 

STRATIGRAPHY AND SEDIMENTARY HISTORY OF THE LAKE 

Recent Sediments 

The sediments exposed on the lake bottom today consist pre- 
dominantly of materials deposited since the end of the Champlain 
Sea episode (about 10,000 years B.P.). The source of this mater- 
ial is (1) unconsolidated glacial deposits transported to the 
lake basin by streams (2) bedrock eroded from the shoreline; (3) 
organic matter from decomposing plants and animals; (4) biochemi- 
cal constituents such as diatom frustrules. Based upon the size 
of past and present lake deltas, it is apparent that rivers have 
played an important role in transporting sediments to the basin. 
The present distribution of lake sands and gravels may be explain- 
ed by wave winnowing. Coarse material, transported by streams to 
the lake is being left near shore. Fine material is being carried 
to the deeper basins. The lake muds, which constitute the deep 
water facies of the near shore sands and gravels, contain a signi- 
ficant fraction of organic matter, as well as biochemical consti- 
tuents. With the possible exception of deltaic deposits which 
have not yet been studied, lake muds constitute the thickest se- 
quences of recent sediments. Thicknesses of up to 80 feet have 
been observed (Chase, 1972). For purposes of discussion, recent 



417 



lake sediments have been grouped into four types - gravels, sands, 
lake muds, and iron manganese concretions. A description of these 
four sediment types is given below: 

Gravels ; - Gravel deposits, as defined by greater than 30 
percent gravel (Folk, 1954), make up less than 4 percent of the 
sediments exposed on the lake bottom. Except for the gravel- 
sized material found in prerecent lake clays, gravels occur pri- 
marily in three areas: (1) shallow nearshore environments; (2) 
surrounding islands; and (3) at the mouths of rivers. Doth in 
nearshore environments and surrounding islands the gravels repre- 
sent lag deposits formed from the sorting of glacial till as well 
as the erosion of local bedrock. Gravels at the mouths of rivers 
are forming as a delta deposit. Former river channels can fre- 
quently be recognized by the distribution of nearshore gravel dep- 
osits . 

Sands :- Sands, defined as having at least 30 percent sand 
(Folk, 1954), cover 22 percent of the lake bottom. The distribu- 
tion of recent sand deposits is much like that of gravel in that 
they occur primarily in nearshore shallow water environments, and 
at the mouths of rivers (Fig. 5) . In many areas they grade shore- 
ward into gravels. The sands are low in organic matter, carbonate 
content, and are texturally and mineralogically immature. 

Muds : - Muds cover approximately three quarters of the total 
area of the lake bottom. They occur primarily offshore in deep 
water (greater than 50 feet) where wave action is at a minimum, 
and in sheltered areas such as the bays. They are continuous 
through a facies change with recent sands. The surface of the 
muds is a grayish to reddish brown hydrosal. Beneath the inter- 
face, the muds are dark gray, uniform in grain size, and generally 
without lamination or structures although carbon smears and mottl- 
ing do occur. The muds typically have a high organic content (up 
to 20 percent) . The inorganic constituents of the muds consist 
of silica grains, clay minerals, and, in some areas, greater than 
50 percent diatom frustrules. 

Iron-Manganese Concretions :- "Manganese nodules" have been 
discovered in seven areas of Lake Champlain (Fig. 6) . Only in the 
east limb, however, are they abundant and do they form well-devel- 
oped concretionary structure. Here they occur in an almost pure 
state. In other areas the concretions are mixed with a terrigen- 
ous matrix which constitutes 90 percent or more of the sample. 
They occur primarily on shallow water platforms in water depths 
less than 40 feet and in areas where sedimentation rates are low 
(Fig. 6). Where concretions do occur at greater depths, they are 
found on slopes adjoining shallow water shelves, suggesting trans- 
portation off the shelves and down the slopes after formation. 
The nodules are associated with sandy sediments indicating that 
they are forming in high energy environments (Johnson and Hunt, 
1972) . 



418 



(^-■tt 1^. ^HJlMtNISOFL*«E CHAMW. 



MAP 2 




Figure 5. The Distribution of Sand in Central Lake Champlain. 



419 



MAP 2 




Figure 6. Bathymetry, Profile Locations, and Sampling Sites, 
Central Lake Champlain. 



^20 



In size they vary from a few millimeters in diameter to 
greater than 10 centimeters; in shape, they range from spherical 
to reniform to discoidal. In well-developed concretions, light 
and dark brown bands may be seen in polished sections. Sand 
grains frequently form the nucleus. The geochemistry of the nod- 
ules was studied by Johnson (1969). The composition may be div- 
ided into two components, terrigenous and chemical. The terrigen- 
ous portion constitutes about one-third of the nodule by weight 
and consists predominantly of agglutinated fine-grained quartz and 
clay minerals. The dominant constituents in the chemical fraction 
are Fe20338.5% and MnO 10.5% (east limb of lake). The nodules 
have a scavenging effect on trace metals. Maximum values of 410 
ppm for cobalt, 605 ppm for copper and 585 ppm for zinc have been 
observed. 

Prerecent Sediments 

A fifth sediment type, lake clay, is exposed over a small 
area of the lake bottom, (1) on topographic highs where wave act- 
ion is effective in erosion or preventing deposition of younger 
sediments and (2) where deep currents prevail. These sediments 
consist of two units. One was deposited in proglacial Lake Vermont 
during the retreat of the Pleistocene ice sheets, approximately 
13,000 - 12,000 B.P. The second lake clay was deposited in the 
Champlain Sea which existed around 12,000 B.P. to 10,000 B.P. The 
maximum extent of both Lake Vermont and the Champlain Sea was con- 
siderably greater than present Lake Champlain. The only sediments 
of Lake Vermont or Champlain Sea origin which have been recognized 
in Lake Champlain are these lake clays. Presumably most of the 
coarser nearshore facies have been stranded away from the lake at 
higher elevations. These two units have been traced subsurface by 
sub-bottom profiling (Chase, 1972). Champlain Sea sediments, which 
have a known maximum thickness of about 100 feet, may be most eas- 
ily recognized by the presence of foraminif era. More than a dozen 
genera have been recognized by Egolf (1972) from a single core at 
the mouth of Shelburne Bay. No fossils are known from the under- 
lying Lake Vermont unit which has a total thickness in excess of 
150 feet. Bedrock or till is believed to rest beneath these lake 
clays. A description of the lake clays, as exposed on the lake 
bottom today, is given below. 

The clays are dense, sticky, and extremely poorly sorted, 
containing material ranging from clay size to cobbles several inch- 
es in diameter. Larger particles, including sand and gravel, are 
concentrated at the sediment-water interface and are dispersed 
through the sediment to a depth of at least several feet beneath 
the surface. The water-sediment interface is not a hydrosol as it 
is with the recent muds but is so well-compacted that it is diffi- 
cult to penetrate. Wet, the clays typically are brown to yellow- 
brown in color at the interface and dark brown to dark grey below 
it. The clays also differ from the muds in their low organic con- 



HCX 



tent. The recent lake muds contain from 5% to 20% organic matter, 
whereas the lake clays have an organic content which rarely ex- 
ceeds 5%. The lithology of the gravel fraction of the clay is var- 
iable and consists of metamorphic rocks, shales, and sandstones 
which outcrop within the drainage basin. 

Sediments of Cultural Origin 

In addition to the five naturally occurring sediments dis- 
cussed above, sawdust, wood chips, paper waste, and cinders occur 
in several areas of the lake. Locally, as at the mouth of the 
Bouquet River, wood chips and sawdust, discharged during lumbering 
operations, and sludge at the mouth of Ticonderoga Creek discharg- 
ed during paper production constitute a major portion of the sedi- 
ment (See Folger, this guidebook). Cinders, which reflect the 
course of steamer traffic of past decades, are also abundant in 
some areas. 

ADDITIONAL PROPERTIES OF SEDIMENTS 

Chemical Properties :- The chemical properties of the lake 
sediments have not as yet been studied in any detail though sev- 
eral aspects are now being investigated. Notes from a few pre- 
liminary studies are, however, included here. Scattered carbon- 
ate analyses of lake sediments were made by Johnson (1967) who 
found carbonate percent to be remarkably low (loss than 2 percent) , 
considering the abundance of limestone bedrock in the drainage bas- 
in. The phosphorus content of the recent muds of St. Albans Bay 
was studied by Corliss and Hunt (1971) who found values twice as 
high in St. Albans Bay (1100 ppm) as in Lapan Bay, the control bay, 
which suggests nutrient build-up^ presumably resulting from the 
discharge of sewage by the Town of St. Albans. Analyses of trace 
metals include the work of Cronin (1970) who analyzed the lead 
content in sediments taken on a traverse from Burlington Harbor 
westward to central Lake Champlain. He found that the highest 
concentrations occur in Buriington Harbor. Additional analyses by 
Hunt of lead, zinc, and chromium suggest that surface sediments 
have a higher concentration than underlying sediments, indicating 
cultural pollution. Chase (1972) analyzed for calcium and magnes- 
ium in sediment and interstitial waters of lake cores. Some var- 
iations were found but the interpretation of these data is not 
yet clear. An extensive study of trace metal concentrations 
utilizing core data is now underway by April (1972). 

Organic Properties ;- About 500 surface samples, primarily 
from central Lake Champlain, have been analyzed for total organic 
matter (Hunt, 1971). Values range from less than 1% to 22%. The 
data show that (1) organic content increases from the shoreline 
lakeward, (2) is positively correlated with increasing water depth, 
(3) increases with decreasing grain size. Numerous exceptions to 
these generalizations do occur. Some are easily explained, as in 



^4-22 



the vicinity of Ticonderoga Creek where organic values of 22% 
were observed. This organic matter almost certainly is a pro- 
duct of industrial pollution (see Folger, this guidebook) . 

Mineralogical Properties 

Heavy Minerals ;- Townsend (1970) studied the heavy miner- 
al content of sediments from the Ausable and Lamoille Rivers. He 
recognized two mineral assemblages: one, present in the western 
portion of the lake, is derived from the igneous and metamorphic 
rocks that occur in the drainage basin to the west. The second 
assemblage is best developed on the east shores of the lake and 
reflects the lower grade metamorphic source rocks which are expos- 
ed in the eastern portion of the drainage basin. In the central 
portion of the lake these two assemblages mix. 

Clay Minerals ;- Studies of clay-mineral distribution within 
the confines of Lake Champlain are in their infancy. Millett (1967) 
conducted X-ray diffraction studies of approximately 100 surficial 
sediment samples between Valcour Island, New York, and Thompson 
Point, Vermont. He found illite and chlorite are the dominant 
clay minerals with most samples having an illite ; chlorite ratio in 
the range of 2.3 to 3.7. Some kaolinite is present in sediments 
from the Bouquet and Auseible Rivers which drain from the west side 
of the lake, but kaolinite appears to be essentially absent from 
lake sediments. 

In addition, approximately 250 samples were checked by Bucke 
from 7 cores to determine clay mineral content vertically through 
the sediments. Millett 's findings were supported in that the 
only significant clay minerals are illite and chlorite. The aver- 
age illite ; chlorite ratios in the cores range from 3.3 to 5.0 
with a mean of approximately 4.2, about one higher than Millett 's 
surface samples. This particular study was essentially a "shot- 
in-the-dark" with no previous knowledge of lithologies being pene- 
trated by the cores. Current investigations of vertical clay min- 
eral distribution is directed to determine if any consistent var- 
iations are detectable among Lake Vermont, Champlain Sea, and Lake 
Champlain sediments. Chase (19 72) ran preliminary studies toward 
this end. Some suggestions of vertical variation are present, 
but as yet data is not consistent nor extensive enough to esta- 
blish any real trends. 



^23 



STOP DESCRIPTIONS 

Stop 1 . Telemetric buoy, Burlington Harbor . - We will pass along- 
side a buoy that has been installed by the Lake Champlain Studies 
Center to collect and transmit environmental data. The buoy nor- 
mally transmits by radio every three hours to a base unit at the 
University which prints out the data in digital code. At present 
the buoy transmits information on wind speed and direction, air 
temperature, and water temperature at two depths. An accellero- 
meter is being used in an attempt to measure sea state. 

Stop 2 . Reference Stations . - This stop, in 300 feet of water, is 
a reference station that has been sampled since 1965. A tempera- 
ture profile will be obtained with a bathythermograph, demonstrat- 
ing temperature variation with depth; and water samples will be 
collected at several depths for chemical analyses, and a plankton 
tow will be obtained for specimens of Mysis . In addition, a sam- 
ple of recent lake muds will be collected. 

Stop 3 . Four Brothers Islands . - Cores from this area contain 
foraminifera indicating that these sediments were deposited in 
the Champlain Sea. The surface sediments on the Four Brothers rise 
contain a relatively high percentage of sand which distinguishes 
them from the encircling recent lake muds (Figure 5). The Four Broth- 
ers are situated on a topographic high and are subjected to exten- 
sive wave action, therefore, the sands may represent lag deposits 
rather than undisturbed pre-Lake Champlain sediments. The primary 
purpose of this stop is to obtain a piston core of Champlain Sea 
sediments . 

Stop 4 . Valcour Island . - This stop along with stops 5 and 6 will 
constitute a west-east traverse designed to show differences in 
thermal patterns, benthos, and sediment types across the lake. The 
interpretation of the sedimentary sequence based upon sub-bottom 
profiling data is given in figure 7. At this stop a bathythermo- 
gram will be taken and a grab sample will be collected and sieved 
for benthos. The waters surrounding Valcour Island were the site 
of the first naval engagement of the Revolutionary War. 

Stop 5 . Central Lake . - Sediments here are Champlain Sea deposits, 
underlain by Lake Vermont clays (Figure 7) . At the surface the 
Champlain Sea deposits contain up to 40% sand as well as gravel- 
sized particles several inches in diameter, suggesting winnowing. 
Recent lake muds surrounding these Champlain Sea deposits indicate 
that restricted deep currents may be responsible for the winnowing. 

Stop 6 . Providence Island . - To complete the traverse profile a 
bathythermogram will be taken at this station, the benthos will be 
sampled, and a plankton haul will be made. 



i^2h 



stop 7 . Winooski Delta (Optional) - This is a shallow-water stop 
at the mouth of the Winooski River. The influence of the river 
on the lake's bathymetry may be seen in figure 5. The sediment 
contains up to 80% sand. The area was considered by engineering 
firms as a source of fill in the construction of the Burlington 
beltline but a more economical land source was eventually select- 
ed. Deposition from the Winooski and Lamoille Rivers has virtual- 
ly isolated Malletts Bay from the main lake. Note the tombolo 
forming the railroad crossing between the mainland and Grand Isle. 
As we return to Burlington Harbor, note the Champlain overthrust 
exposed on Lone Rock Point. 



^25 



REFERENCES CITED 

April, Richard, 1972, Trace Element Distributions in the Sediments 
, of Lake Champlain. M. S. thesis, in preparation. 

Chapman, C. H., 1937, Late glacial and post-glacial history of 

Champlain Valley: Am. Jour. Science, 5th ser. , v. 34, p. 89-124. 

Chase, Jack S., 1972, Operation UP-SAILS, Sub-bottom Profiling in 
Lake Champlain. M. S. thesis. University of Vermont, 104 p. 

Corliss, Bruce H. and Hunt, Allen S., 1972, The Distribution of 
Phosphorus in the Sediments of St. Albans Bay, Lake Champlain. 

Cronin, Francis, 1970, Lead content of lake sediments in Lake Cham- 
plain. Unpublished reoort. 

Egolf, R. Terrance, 1972, Report on a Study of the Foraminifera of 
the Champlain Sea at Shelburne Bay, Vermont. Senior thesis. 
Department of Geology, University of Vermont, 2 5 p. 

Fillon, Richard H., 1969, Sedimentation and Recent Geologic History 
of the Missisquoi Delta. M. S. thesis, University of Vermont, 
112 p. 

Folk, R. L. , 1954, The Distinction between grain size and mineral 
composition in sedimentary rock nomenclature: Jour, of Geology, 
V. 62, p. 344-359. 

Henson, E. B. , 1966, A review of Great Lakes benthos research. 
Univ. Mich., Grt. Lakes Res. Div. , publ. n. 14, p. 37-54. 

Hunt, A. S., Townsend, P. H., and Boardman, C. C. , 1968, Lake 
Champlain Drainage Basin, Champlain Research Reports, Issue 
No . 2 . 

■ , Boardman, C C. , and Stein, D. E., 1970, The volume of Lake 

Champlain, Champlain Research Reports, Issue No. 3. 

, 1971, Bottom Sediments of Lake Champlain: 1965-1971; A Com- 
pletion Report to the Office of Water Resources Research, the 
Department of the Interior, 127 p. 

Hutchinson, G. E., 1957, A treatise on limnology, v. 1, Wiley, 
N. Y. , 1015 p. 

Johnson, David G. , 1967, Carbonate Content of Some Recent Lake 
Champlain Sediments. Unpublished report. 

, 1969, Ferromanganese Concretions in Lake Champlain. M. S. 



thesis. University of Vermont, 96 p. 



426 



, and Hunt, Allen S., 19 72, The occurrence of Ferromanganese 

Concretions in Lake Champlain. Limnology and Oceanography. Un- 
dergoing revision. 

Legge, Thomas N., 1969, A study of the seasonal abundance and 
distribution of calanoid copepods in Burlington Bay, Lake 
Champlain. Unpublished M. S. thesis, Department of Zoology, 
University of Vermont, 133 p. 

MacClintock, Paul, and Terasmae, J., 1960, Glacial history of 
Covey Hill: Jour. Geology, v. 68, p. 232-241. 

Millett, John, 1967, Clay Minerals of Lake Champlain (Vermont). 
M. S. thesis. University of Vermont, 44 p. 

Potash, M. , 1965, A study of two bays of Lake Champlain. Univ. 
iMich., Grt. Lakes Res. Div. , publ. n. 13 (abstract). 

, and Henson, E. B. , 1966, Oxygen depletion patterns in 



Malletts Bay, Lake Champlain. Univ. Mich., Grt. Lakes Res. 
Div., publ. n. 15, p. 411-415. 

, Sundberg, S., and Henson, E. B., 1969a, Characterization 



of water masses of Lake Champlain. (in press) . 

, , and , 1969b, Epilimnial oxygen reduction dur- 
ing fall turnover m Malletts Bay. Proc. Int. Assoc. Grt. 
Lakes Res., (in press). 

Ricker, K. E., 19 59, The origin of two glacial relict crustaceans 
in North America, as related to Pleistocene glaciation: Can. 
Jour. Zool., V. 37, p. 871-893. 

Sherman, John W. , 1972, Post-Pleistocene Diatom Stratigraphy in 
Cores from Lake Champlain, Vermont. M. S. thesis. University 
of Vermont, 81 p. 

Stewart, David P., 1961, The Glacial Geology of Vermont. Vt. 
Geol. Surv. Bull. n. 19, 124 p. 

, and MacClintock, Paul, 1969, The Surficial Geology and Pleis- 



tocene History of Vermont. Vt. Geol. Surv. Bull. n. 31, 251 p. 

Terasmae, J., 1959, Notes on the Champlain Sea episode in the St. 
Lawrence lowlands, Quebec: Science, v. 130, p. 334-335. 

Townsend, Peter H., 1970, A Study of Heavy Mineral Dispersal from 
the Ausable and Lamoille Rivers (Lake Champlain). M. S. thesis. 
University of Vermont, 60 p. 

Woodworth, J. B., 1905, Ancient water levels of the Hudson and 
Champlain Valleys. N. Y. State Mus . Bull. n. 84, p. 65-265. 



428 



I 



Paleontology Cover page: Thin section photomicrograph of rocks 
from the Day Point Formation on Isle La Motte, western Vermont, 
For details see Finks, Shaw and Toomey (Trip P-1, this guide- 
book . ) 



kZ9 



Trip P-1 



ORDOVICIAN PALEONTOLOGY AND STRATIGRAPHY OF THE 

CHAMPLAIN ISLANDS 



R.M. Finks F.C. Shavv D.F. Toomey 

Queens College Lehman College Amoco Production Co, 

Flushing, N.Y. Bronx, N.Y. Tlsa, Okla. 

This trip focuses on the Chazy Limestone as ex- 
posed on southern Isle LaMotte , Vermont. The first part of 
the trip, conducted and described on the following pages by 
Shaw, covers the lower and middle parts of the Chazy at Stops 
1, 2, and 3 on Figure 4. The second part of the trip, describ- 
ed by Finks and Toomey in the subsequent section, is a walk- 
ing tour through the spectacular reef facies of the Chazy, 
starting 1/2 mile NE of Stop 2 on the same figure (Fig. 4, 
see also Fig. 2 of Finks and Toomey). 

Paleontology and Stratigraphy of the Chazy Group (Middle 
Ordovician) , Champlain Islands, Vermont.* 



F.C. Shaw 



Introduction 

The Chazy Limestone (the oldest Middle Ordovi- 
cian formation of the Champlain Valley) was first named by 
Emmons (1842) from exposures 15 miles north of Plattsburgh 
at Chazy, New York. Here and elsewhere in the northern Valley 
(Fig. 1) the unit outcrops on a variety of normal fault blocks. 
Given the low dips and heavy cover, Chazy stratigraphy is most 
easily understood from various shore outcrops around Lake 
Champlain. Valcour Island, SE of Plattsburgh, offers perhaps 
the best section of the Chazy and has been intensively stud- 
ied (Raymond, 1905; Hudson, 1931; Oxley and Kay, 1959; Fisher, 
1968; Shaw, 1968). The Isle LaMotte exposures to be covered 
on this trip are those studied by many of the same authors 
and, in addition, display the lower contact of the Chazy 
with the underlying Ordovician dolostones of Canadian age. 



*Most of the following discussion and figures are excerpted 
from the trip run by Shaw for the New York State Geological 
Association (Plattsburgh, 1969) and from Shaw (1968). 



CANADA_ 

'unTted states 




Figure 1. INDEX MAP 

of 

Champlain Valley 

and portions of 

New York .Vermont and Quebec 

(area of figure ^) 

EXPLANATION 



Pleistocene (sands, clays) 



Post-Chazy Ordovician sedimentary rocks 
(mainly shales) 



Chazy Group (limestones) 



Pre-Chazy Cambrian-Ordovician sedimentary rocks 
( sandstones, dolostones) 



Cambrian-Ordovician metamorptiic strata 



Precambrian rocks 

(gneiss, metanorthosite.chornockite, marble, quartz ite) 



@ Chazy areo 



Valcour area 



@ Plattsburgh quadrangle 

(RP) Rouses Point quadrangle 



Geology modified from D.W Fisher etal., (1962) 



SCALE IN MILES 
5 



O 3J 

X m 
O 2 
C H 
-DO 

2 



o 

I 
> 

M 

-<: 
o 

XI 

o 

c 

-0 



CD 

m 
m 



o 

CD 
3) 
O 

c 



Hathaway Formafion 
orgillite, chert, groywocke 



Iberville Formation 
non-calcareous shale 



Stony Point Formation 
colcoreous shale 



Cumberland Head Argillite 



Glens Foils Limestone 

Montreol and Larrabee 



Isle Lo Motte Limestone 

ond Lowville 



Valcour 
Limestone and Shole 



Crown Point Limestone 



Day Point 
Limestone and Sandstone 






fi^' 






t Tt . : > 



1,3^;3^ 



t7+;+;+ 



t^S 



Tr^rr^T 



-T^-r 



Providence Island Dolostone 



Fort Cassin 
Limestone and Dolostone 



Spellman 
Limestone and Dolostone 



Gutting Dolostone 




Whitehall Dolostone 



Ticonderoga Dolostone 



^ V \ ^ 



V,V >■,■■>;■■ A 



**JJ. 



Barneveld-Wilderness 
Stages 



Chazyan Stage 



late 



middle 



early 



O 

IT 

o 

3 
■o^ 

o 

2" 
q' 

ZJ 

C/) 
fD 

-^ 



O 

o 

o 

Q- 

o' 

cn 

CD 

cd' 

C/l 



o 
:d 
o 
o 
< 



Potsdam Sandstone 



VERTICAL SCALE IN FEET 
400-T-| 

200-1 

oH 



> ^ 



Figure 2. Generalized Stratigraphic Column — Champlain Valley 



^32 



In the northern Chcunplain Valley (Valcour Island 
and north to the International Boundary) , the Chazy Limestone 
(now group) consists of about 800 feet of quartz sandstones, 
calcarenites , dolomitic calcilutites and biohermal masses 
(Fig. 3). Three formations, Day Point, Crown Point, and 
Valcour, in ascending order, were proposed by Gushing (1905) 
and have persisted to the present, albeit with some contro- 
versy (Fisher, 1968; Shaw, 1968). Oxley and Kay (1959) fur- 
ther subdivided the Day Point and Valcour into members, 
those of the Day Point (Head, Scott, Wait, Fleury) coming from 
southern Isle LaMotte in the area to be visited. Shaw and 
Fisher experienced difficulty in using the Valcour subdivisions 
outside of their type areas at South Hero, Vermont. 



DESCRIPTION AND INTERPRETATION OF CHAZY GROUP 

LITHOLOGIES 



Day Point Formation 

With the exception of the biohermal masses on Isle 
LaMotte the Day Point consists of a basal, cross-bedded quartz 
sandstone, followed by alternating units of shale, more 
sandstone, calcarenite, and topped with a relatively thick 
(35 feet) calcarenite unit (the Fleury Member). The lower 
sandstone, with its cross-bedding, presence of Lingula as 
nearly the only fossil, and overlying the supratidal Lower 
Ordovician, is probably transgressive and of very shallow 
water origin. This is further borne out by the presence of 
an oolite band in some of the sections around Chazy, New York, 
The source of the sand is unknown and no petrographic studies 
on this formation or on most of the other Chazy units have 
been undertaken. Derivation from Cambrian sandstones exposed 
on lowly emergent land to the west appears feasible. The 
calcarenites are primarily echinodermal in origin, although 
bryozoans and trilobites also occur abundantly, particularly 
in the Fleury (Ross, 1963, 1964; Shaw, 1968). Again, shallow 
water seems indicated, although probably subtidal judging 
from the abundant faunas (compare Laporte, 1968 and Textoris, 
1968) . 

At Valcour Island and on the adjacent shore at Day 
Point, New York, the upper Fleury calcarenites are interbedded 
with dark, muddy limestones, some of which contain the varied 
silicified trilobite fauna described by Shaw (1968). 



^33 



Q_ 
O 

cr 



>- 

M 

< 

X 



c 
o 

£ 



3 
o 
_o 

o 

> 



c 
o 

"5 

E 



o 
a. 

c 

§ 

o 
o 



D 

E 



o 

Q_ 

o 
Q 



Northern Champlain Valley 

Lowville 



Crown Point 



Beech member 



Hero member 



Fleury member 



Waif member 



Scott member 



Head member 




LOWER ORDOVICIAN 
DOLOSTONE 
I 



CL 

O 

cr 

>- 

M 
< 

X 

o 



LOWER ORDOVICIAN 

DOLOSTONE 
I 



VERTICAL SCALE IN FEET 
100 -n 



50- 1 
0-" 



Figure 3. Lifhologic Correlation 



43^ 



Crown Point Formation 

The Crown Point Formation begins where muddy lime- 
stones become the dominant lithology. A striking feature of 
this formation is the abundance of thin (maximum 1/2 inch 
thick) dolomite stringers. Thin section analysis of many of 
these irregular stringers indicates that they are composed of 
argillaceous material, calcite grains, and scattered dolo- 
mite rhombs (Barnett, personal communication, 1969). Judg- 
ing from the abundant faunas (gastropods, trilobites, ostra- 
cods, brachiopods) and their preservation (some trilobites 
and ostracods articulated) , this lithology represents some- 
what deeper and less agitated water. This leaves the origin 
of the dolomite to be explained inasmuch as recent discus- 
sions of dolomite have focused on a supratidal origin. 
Possibly this dolomite is secondary. Similar lithologies 
are known in the Ordovician of the southern Appalachians and 
Nevada and present a good petrologic problem. The 200-300 
feet of the Crown Point Formation has never been subdivided 
into members, attesting to its homogeneity. Twenty-five 
miles south of Valcour Island, at Crown Point, New York, 
nearly the whole section (250 feet) is comprised of Crown Point 
Formation lithology (Fig. 3) . 



Valcour Formation 

The Valcour Formation is characterized by a return 
to calcarenites, interspersed with limestones of Crown Point 
aspect. In addition, much of the Valcour as well as the un- 
derlying Crown Point displays well-developed bioherms con- 
sisting of stromatoporoids, bryozoans, calcareous algae, 
sponges and corals with an accompanying fauna of trilobites, 
brachiopods, cephalopods, and echinoderms. Spectacular exam- 
ples of these will be covered on this trip. The channels in 
these reefs, the packing of these channels with trilobite and 
nautiloid fragments, and the accompanying carbonate sands 
again argue for relatively shallow water, with the more 
typical muddy limestones probably occupying slightly deeper 
basins between. 

The Valcour is overlain by rock units usually assign- 
ed to the Black River Group, although outcrop or exact paleonto- 
logical continuity with the type Black River of central New 
York euid Ontario is difficult to demonstrate (Johnsen and 
Toung, 1960; Hofmann, 1963). 



^35 



PALEOGEOGRAPHIC SETTING OF THE CHAZY GROUP 

As mentioned above, the lower Chazy Group evi- 
dently represents a transgressive sequence over Lower Ordo- 
vician dolostones. The relative thinness, lack of abundant 
elastics, shallow water features, lack of volcanics and pre- 
dominance of "shelly" rather than graptolitic faunas all 
argue for a setting on the platform or at best at the very 
edge of the miogeosyncline. Most paleogeographic reconstruc- 
tions of Chazyan time (Kay, 1947) exhibit this relationship. 
Although the Chazy group thins and disappears southward and 
westward into New York State, lithologically and faunally 
similar units persist northward to the Montreal area and 
eastward into the Mingan Islands of eastern Quebec (Hofmann, 
1963; Twenhofel, 1938; Shaw, ms.). Westward thrusting along 
Logan's Line has covered much of the miogeosyncline to the 
east, leaving us with either unfossiliferous or graptolite- 
bearing rocks which defy exact comparison to the Chazy Group. 
Speculation as to the exact geography of the Appalachian 
geosyncline in this area during Chazyan time is hazardous. 



FAUNAS OF THE CHAZY GROUP 

Raymond (1906) identified three faunal zones in 
the northern Champlain Valley Chazy Group, corresponding 
roughly to the three formations proposed by Gushing (190 5) . 
These were not really assemblage zones in the modern sense 
but relied heavily on two brachiopods and the large gastro- 
pod Maclurites mag nus LeSueur (PI. 1, Fig. 3). Raymond and 
later workers (WelByT 1961; Erwin, 1957; Oxley and Kay, 1959) 
also thought that the trilobite Gla p hurus p ustulatus (Walcott) 
first appeared at the base of the Valcour Formation. All 
of the cibove instances now appear to be examples of local 
abundance and/or facies control, although they are of some 
stratigraphic use locally in the Champlain area. Ross (1963, 
1964), Cooper (1956), and Shaw (1968), using bryozoans, 
brachiopods and trilobites, respectively, were unable to 
make meaningful faunal subdivisions of the Chazy Group. 
Bergstrom (19 71) has summarized the known information of 
Chazy conodonts. Nevertheless, the Group as a whole is 
distinctive, containing as it does the first appearance of 
stromatoporoids , primitive tetracorals, bryozoans (?) , 
and primitive pelecypods. In addition, twenty- four genera 
of trilobites appear first in the North American Ordovician 
here in the Chazy Group. By contrast, graptolites and 
several long-ranging groups of trilobites such as robergi- 
oids and agnostids are absent from the Group, probably as 
a result of facies control or restricted oceanic circulation. 








39 



44 



MJ^ 

^^^7 



46 



45 




40 





43 



5 



49 





437 



Plate 1 



1. Amp hilichas min g anensis ; cranidium, dorsal view x2 , 
"From fine lime mud infilling reef framework at Sheldon 
Lane, New York. 

2. Paraceraurus ruedemanni ; cranidium, dorsal view xl , 
Scime lithology and locality. 

3. Maclurites mag nus ; shell largely recrystallized. Crown 
Point Formation Intersection of NY 348 and 187, SW of 
Chazy Village. 

4. Glaphurus p ustulatus : partial cranidium and thorax, 
dorsal view x4. Same lithology and locality as 1 and 
2. 

5. Rostricellula plena: Valcour Formation, Chazy, New York. 
(From Cooper, 1956) xl. 

6. Pliomerop s canadensis ; complete specimen, lower Valcour 
Formation, east side of Valcour Island, New York, xl. 



Figures 1, 2, 4, 6 also appear in Shaw (1968) 



438 



I 




Figure i+. INDEX MAP OF THE ISLE LAMOTTE AREA, VERMONT 

Horizontal Lines: Day Point Formation 

Dots : Crovm Point Formation 

Vertical Lines: Valcour Formation 

Scale: 1 inch to 1 mile (Modified from Fisher, 1968) 



439 



In sum, the Chazy Group records a diverse marine 
fauna of cratonic aspect, including the very early represen- 
tatives of a number of successful Paleozoic taxa. Exclusion 
of other taxa expected to be present, as well as facies 
dependence of organisms within the various facies of the Chazy 
Group (Shaw, 1968) generate some problems in correlating the 
Group to other North American Ordovician sequences. 



FIELD TRIP STOPS 



PLEASE NOTE: ALL STOPS ARE ON PRIVATE PROPERTY WHICH WE 
HAVE SPECIAL PERMISSION TO ENTER. DO NOT SMOKE IN THE FIELDS, 
KNOCK OVER FENCES, ETC. OTHERS WILL WANT TO RETURN TO THIS 
CLASSIC LOCALITY AFTER YOU. 



Stop 1 - The Head, Isle LaMotte , Vermont, 3 miles SSW of Isle 
LaMotte Village. Lakeshore outcrops of the Providence Island 
Dolostone (Lower Ordovician) and the Day Point Formation (Chazy 
Group) . Dip of both units several degrees to the north. 
Contact well-exposed and at least locally unconformable. 
Locality discussed by Shaw (1968), Erwin (1957). Section mea- 
sured and described by Oxley and Kay (1959). 

Approximately 40 feet of Providence Island Dolo- 
stone is exposed, being very fine-grained, massive, thinly 
laminated, and unfossiliferous. Mud-cracks and a few ripple 
marks complete the picture of a unit deposited in very shal- 
low water. Following Laporte (1967) and Textoris (1968) , the 
environments echo that of dolomite formation described 
from Florida and the Bahamas. No detailed petrologic work has 
been done on this unit. In the absence of fossils, the age 
of this unit is not known. The underlying Fort Cassin Lime- 
stone (not exposed here) is known to be Late Canadian. 

The Chazy Group begins here with about 20 feet of 
quartz sand and siltstones together with minor amounts of 
greenish shale (Head Member of Oxley and Kay, 1959). Ripple 
marks and cross-bedding are common. The fossils consist 
primarily of "fucoids" (probably recording a variety of 
trails, worm tubes and the like) and Lingula. The succeed- 
ing Chazy unit (Scott Member of Oxley and Kay) consists of 
about 40 feet of echinodermal lime sand, cross-bedded in 
some places. Brachiopods ( Orthambonites? ) and indetermina±>le 
trilobite scraps are the chief recognizsible fossils. The 
overlying 15 feet of quartz sandstone (Wait Member of Oxley 
and Kay) appears very similar to the initial sandstone. 



kkO 



This second sandstone is followed by a thick (115 
feet) lime sand (Fleury Member of Oxley and Kay) which occupies 
most of Scott Point and The Head south of the road. Much 
of the unit is composed of echinoderm fragments, although 
little is known about the actual morphology of the creatures 
involved. Both the fragmental nature of the fossils and the 
frequently observed cross-bedding argue for considerable 
agitation of the ocean bottom. 

Sto p 2^ - Seune vehicle location as Stop 1. Upper Fleury Member 
of Day Point Formation and overlying Crown Point Formation. 
200 yards south of the right angle bend in the road is loc- 
ity R 25 (Shaw, 1968) which yielded 12 genera of trilobites, 
including Sp haeroxochus and Ceraurinella , from a particularly 
coarse poclcet in the upper Fleury lime sands. Gastropods 
( Raphi stoma ) and brachiopods ( Orthambonites ?) are also pre- 
sentT This same stratigraphic level elsewhere, particularly 
1 mile to the NE, displays spectacular bryozoan bioherms and 
the very early tabulate coral Lichenaria (Pitcher, 1964) 
to be seen later on this trip. 

About 50 yards north of the road at this same 
stop, the silty, Maclurites-bearing limestones of the Crown 
Point appear. The actual contact with the Day Point is not 
visible but the lithologic change is evident. The Crown Point 
here contains several modest bioherms which have not been 
studied in detail. The earliest known stroma toporoids (Pitcher, 
1964) are known to be important reef builders nearby in this 
unit and doubtless are dominant here as well. 

Sto p 3 - Fisk Quarry, 2.5 miles SSW of Isle LaMotte Village. 
Middle Crown Point Formation, consisting of fine-grained, 
dark, silty limestone with buff-colored dolomitic partings. 
This is "typical", non-reef Crown Point lithology. However, 
in the quarry wall eind some of the cut blocks, small "reef- 
lets" can be seen. These are assumed to be largely stroma- 
toporoids and calcareous algae, although they have not been 
studied as intensively as the reefs at the same horizon to 
the east. Evidently, these reef masses could grow at some 
depth in relatively silty waters. The mechanism of their 
establishment thus does not appear to be tectonic. Maclurites 
(large gastropod, rare) and a few trilobites and brachiopods 
may possibly be collected from the limestone, although they 
are not abundant. 

Acknowledgements : 

For field work assistance and guidance, I eun 
grateful to Donald Fisher and Harry Whittington. The access 
to southern Isle LaiMotte is via the kindness and interest 
of Mr. Selby Turner. 



k^l 



REFERENCES CITED 



Bergstrom, S.M. , 1971, Correlation of the North Atlantic 
Middle Upper Ordovician Conodont Zonation with the 
Graptolite Succession: Mem, du Bureau de Recherches 
Geologiques et Minieres #73, pp. 177-187. 

Cooper, G.A. , 1956, Chazyan and related brachiopods : Smith- 
sonian Misc. Pubs, V. 127 (2 parts), pp. 1023. 

Cushing, H.P., 1905, Geology of the northern Adirondack 
region: N.Y. State Mus. Bull. 95, pp. 271-453. 

Emmons, Ebenezer, 1842, Geology of New York, Part 2 — Survey 
of the 2nd Geological District: Albany, p. 437. 

Erwin, R.B., 1957, The geology of the limestones of Isle 

LaMotte and South Hero Island, Vermont: Vermont Geol. 
Survey Bull. 9, p. 94. 

Finks, R.M. and Toomey , D.F., 1969, The paleoecology of 

Chazyan (Lower Middle Ordovician) "reefs" or "mounds". 
New York State Geol. Assoc. Guidebook, p. 9 3-134. 

Fisher, D.W. , 1954, Lower Ordovician (Canadian) stratigraphy 
of the Mohawk Valley: Geol. Soc. Amer. Bull., v. 65, 
pp. 71-96. 

Fisher, D.W., 1968, Geology of the Plattsburgh and Rouses 
Point, New York-Vermont Quadrangles: New York State 
Museum and Science Service, Map and Chart Series, 
#10, p. 51, pi. 2. 

Flower, R.H., 1958, Some Chazyan and Mohawkian Endoceratida: 
Jour. Paleontology, v. 32, pp. 433-458. 

Hofmann, H.J., 1963, Ordovician Chazy Group in Southern 

Quebec: Am. Assoc. Petrol. Geol. Bull., v. 47, pp. 
270-301. 

Johnsen, J.M. and Toung, G.D,, 1960, Pamelia east of the 
Frontenac Axis in New York State: Geol. Soc. Amer. 
Bull. 71, p. 1898 (abs.) 

Kraft, J.C., 196 2, Morphologic and systematic relationships 
of some Middle Ordovician Ostracoda: Geol. Soc. Amer. 
Mem. 86, p. 104. 

Laporte, Leo, 196 8, Ancient Environments, Prentice-Hall, pp. 116, 



442 



Oxley, P. and Kay, M. , 1959, Ordovician Chazyan Series of 
the Champlain Valley, New York and Vermont and its 
reefs: Amer. Assoc. Petro. Geol. Bull., v. 43, 
pp. 817-853. 

Pitcher, Max, 1964, Evolution of Chazyan (Ordovician) reefs 
of eastern United States and Canada: Bull. Can. Pet. 
Geol., V. 12, pp. 632-669. 

Raymond, P.E., 1905, The fauna of the Chazy limestone: 
Am. Jour. Sci., ser. 4, v. 20, pp. 353-382. 

Ross, J. P., 1963, Ordovician Cryptostome Bryozoa; standard 

Chazyan Series, New York and Vermont: Geol. Soc. Amer. 
Bull., V. 74, pp. 577-608. 

Shaw, F.C., 1968, Early Middle Ordovician Chazy Trilobites 
of New York: N.Y. State Mus . and Sci, Ser., Mem. 17, 
p. 163. 

Shaw, F.C., 1969, Stratigraphy of the Chazy Group: N.Y. State 
Geol. Assoc. Guidebook, pp. 81-92. 

Textoris, D.A. , 1968, Petrology of Supratidal, Intertidal, 
and Shallow Subtidal Carbonates, Black River Group, 
Middle Ordovician, New York: 23rd Int. Geol. Cong., 
V. 8, pp. 227-248. 

Toomey, D.F. and Finks, R.M. , 1969, Middle Ordovician (Chazyan) 
mounds, southern Quebec, Canada: a summary report: 
N.Y. State Geol. Assoc. Guidebook, pp. 121-134. 

Welby, C.W., 1961, Bedrock geology of the central Champlain 

Valley, Vermont: Vermont Geol. Survey Bull., 14, p. 296, 



443 



PALEOECOLOGY OF CHAZY REEF-MOUNDS* 



Robert M. Finks Donald F. Toomey 

Queens College and Amoco Production Co. 
Flushing, N. Y. Tulsa, Okla. 



REEFS AS BIOLOGIC COMMUNITIES 

Geologists have conunonly concerned themselves With reefs as 
a problem in the building and maintenance of a framework in the 
face of the destructive effects of wave-energy. From the point of 
view of the reef orgeuiisms the parcmount aspect of the reef envir- 
onment may well be the opportunities it provides for interactions 
between organisms. To use an analogy which may be appropriate on 
many levels, the former approach is like viewing a city as a pro- 
blem in architecture, while the latter is like viewing a city in 
terms of social interactions. What draws people to cities is that 
they provide a maximum availeibility of functional relationships, 
or to use the equivalent biological term, of ecologic niches. The 
high population density of a city, as well as of a reef, is both 
the necessary condition for such functional diversity as well as 
an ultimate result of it. 

As with cities, one of the important problems of a reef is 
the pollution of its environment by its own meted>olism. In parti- 
cular, the depletion of oxygen and the production of nitrogenous 
wastes are the most acute problems. The solution adopted by the 
inhabitants of modern coral reefs is the development of a symbio- 
sis with certain phytomastigophora, termed zooxamthellae, which 
live in the tissues of reef organisms and have been shown to aib- 
sorb nitrogenous materials. In living coral reefs zooxanthellae 
are present in scleractinians , sponges, and even the giant clam 
Tridacna. It is likely that the Scleractinia had this adaptation 
well back into the Mesozoic, for hermatypic Scieractinia and their 
reefs go back at least to the Jurassic, and they form the last 
part of an ecologic succession, or sere, in late Triassic reefs 
(Sieber, 1937). Whether this was true of Paleozoic reef organisms 
is not known. Certainly, calcareous algae were present in Paleo- 
zoic reefs and have continued to those of the present day. These 
free- living algae also contribute to oxygen replenishment and 
nitrogenous waste absorption. They must have been as essential 
to ancient reefs in this metabolic function as in their well- 
known frame-building properties. 

TROPHIC RELATIONS IN THE CHAZY REEFS 

The principal reef-building organisms of the Chazy reefs 
are stromatoporoids ( Cystostroma , Pseudosty Iodic tyon or Stromato - 

* This discussion is a revised version of the trip run by Finks 
and Toomey for the New York State Geological Association (Platts- 
burgh, 1969). 



kkk 



cerium ) , lithistid sponges ( Zittelella Anthaspidella ) , tabulate 
corals ( Lamottia or Lichenaria" , Billingsaria y Eof letcheria ) , bry- 
ozoa (Batostoma, Cheiloporella' ^ Atactotoechus ) ~, and calcareous 
algae ( Soleno'po'raT^phaerocodium or Rothpletzella ^ Girvanella ) . 
In addition, several trilobites ( Glaphurus , Pliomerops and buma- 
stids) and numerous pelmatozoan fragments are found in such inti- 
mate physical association with the reef as to be likely inhabi- 
tants of its surface. The large gastropod, Maclurites , and many 
genera of large nautiloids, are very abundant in the pelmatozoan- 
brachiopod calcarenites between the reefs, in calcarenite-f illed 
channels cut into the reefs, and also in calcilutite-f illed pock- 
ets or channels within the reefs. It is likely that these vagile 
organisms were also regular participants in the foodchain of the 
reef community. 

Unlike modern reefs, in which macrophagous , carnivorous 
coelenterates are the dominant element, and feed upon an abundant 
fauna of small nekton, these Middle Ordovician reefs are dominated 
by suspension feeders. This is especially true when one considers 
the recent reinterpretation of stromatoporoids as sponges (and 
therefore suspension feeders) (Hartman and Goreau, 1970) belonging 
to a little-known group that today participate in living coral 
reefs. The only possible non-suspension feeders in the Chazy 
reefs are the tabulate corals, presumably micro-carnivorous, and 
the trilobites, which are possibly detritus feeders (if not sus- 
pension feeders). 

Maclurites is an archaeogastropod, and presumably grazed on 
algae. It is the largest of the primary consumers of the Chazy 
beds. The nautiloids may have fed on the Maclurites . If so, they 
ate the soft parts without breaking the shells , for most of the 
large shells are whole. The possibility that some of the nauti- 
loids "grazed" on the sessile benthonic invertebrates should not 
be discounted, for these Middle Ordovician cephalopods are not far 
removed in evolution from the late Cambrian ellesmeroceratids , 
whose short, relatively non-buoyant shells indicate a vagile ben- 
thonic adaptation. Although the Chazyan nautiloids had buoyant 
shells and were probably gOod swimmers, they may have retained an 
interest in bottom feeding. Apart from the cephalopods we have 
no evidence for other large carnivores. 

The Chazy reefs are thus a community in which the benthos 
were fed primarily from suspended matter or plankton. Even the 
corals had very small polyps and could not have eaten anything 
very much larger than a few millimeters across. This is surely a 
reflection of the paucity of larger nekton or vagile benthos on 
which to feed. Only the snails and cephalopods provide a larger 
fauna, and may have formed a side loop to the general food chain, 
the cephalopods feeding primarily on the snails. 

Reefs earlier than the Chazy consist only of algae, or else 
include the demosponge Archaeoscyphia or possible sponges, such as 



^*f5 



Archaeocyatha which were not likely to be anything other than sus- 
pension feeders. In the Silurian, corals become much more impor- 
tant, and one begins to see carnivorous macrophagy becoming a more 
important element in the trophic relationships of reef faunas. 
Silurian reefs are still dominated by tabulate rather than rugose 
corals among the carnivores, and thus consumed mainly small vagile 
animals. The suspension feeding element (bryozoa, stromatoporoids) 
is still strong in Silurian reefs. It is not until Devonian times 
that the large rugose corals become a dominant element in reefs, 
probably not without connection with the fact that this was the 
first time that fish and other large nekton appear in abundance, 

DEVELOPMENT OF REEF FAUNAS 

Within the Chazy Group the reef faunas show a progressive in- 
crease in diversity with time (Pitcher, 1964), The earliest reefs, 
in the lower Day Point Formation (Scott Member) , are built of bry- 
ozoans only, and chiefly of one species, or at most two. These 
early benthic concentrations are, like their predecessors, of sus- 
pension feeders only. In the middle of the Day Point (Fleury Mem- 
ber) the Lamottia biostrome introduces the oldest-known coral in 
the world, which is also the oldest-known sessile carnivore with a 
skeleton. (The only older sessile carnivore is a possible anemone 
from the middle Cambrian Burgess Shale, and the only older vagile 
carnivores are the early Ordovician starfish, and the late Cambri- 
an and early Ordovician nautiloids). It is possible at this mom- 
ent in the history of the earth that it first became profitable 
for a carnivore to sit and wait for its food to come to it. This 
coral appears to have lived in a different environment from the 
bryozoa, although probably nearby. The corals 'are often fragment- 
ed and the fragments overgrown by bryozoa. Pitcher (1964, p. 648) 
considers the corals to have been transported into the area of 
outcrop, and there to have acquired their coatings of bryozoa. 

Immediately above the Lamottia biostrome, in the upper Day 
Point, bryozoan mounds again develop (the "circular bryozoan reefs" 
of figure 1), On the surfaces of these circular mounds the lamin- 
ar bryozoans that built them enclose large cystoid stems and small 
lithistid sponges, all in life-position and obviously part of a 
regular reef association (seeplatel, figure 1), These bryozoan- 
cystoid-sponge mounds foreshadow the richer fauna of the Crown 
Point reefs. Just beneath the Crown Point contact, there is an- 
other type of mound, built only of branching bryozoa (the "align- 
ed bryozoan reefs" of figure 1). The colonies are relatively 
large and unbroken and seem to be preserved in place. An environ- 
mental difference (quieter water?) may account for this second 
type of mound. 

In all the Day Point reefs algae are seemingly missing. In 
the Crown Point Formation the reef faunas are more diverse, and 
include algae, stromatoporoids, lithistid sponges, and corals 



^^6 



( Billingsaria y not Lamottia ) along with the bryozoan species that 
built the earlier mounds . The algae were not immediately availa- 
ble to the reef animals for food, but probably performed an anti- 
pollutant function. They may have been eaten by soft-bodied meio- 
benthos which were subsequently consumed by the corals, but the 
principal flow of organic matter must have been from the phyto- 
plankton directly, or through zooplankton, to the reef animals, 
and from there, through the intervention of bacteria, back to the 
benthic algae and to the phytoplankton as dissolved molecules, or 
recycled through the sponges in the form of whole bacteria, which 
may be a principal food of sponges (Rasmont, in Florkin and Scheer, 
1968). That the Crown Point environment was in general one of 
high productivity is demonstrated by the abundance of the large 
snail Maclurites magnus , which is virtually a guide fossil to the 
formation, as well as of the large nautiloids that may have fed 
on it. The abundance of algae outside the reef environment (dead 
Maclurites and nautiloid shells are frequently encrusted by them) 
undoubtedly provided a firm base for the overall food chain as 
well as a food supply for the Maclurites . 

In the yalcour Formation the faunal complexity is maintained 
and the reef assemblage differs little from that of the Crown Point. 

In the Chcunplain Valley and elsewhere the Crown Point reefs 
represent the earliest appearance of a complex reef-building com- 
munity. It is worth noting that the animals involved (stromato- 
poroids, lithistid sponges, tabulate corals, and bryozoa) are 
very nearly the earliest representatives of their respective tax- 
onomic groups. In large part this new complexity is due to the 
evolution of new life. Earlier reefs, even the most complex known, 
such as the early Ordovician mounds of Texas (Toomey, 19 70) , are 
built of only a few organism types, usually algae and sponges. 

The abundance of sponges in the Crown Point and early Val- 
cour reefs deserves consideration, for it can be related to the 
general evolution of hermatypic organisms. Sponges are not com- 
mon reef-building animals. During the period when tabulate and 
rugose corals were abundant, and during the periods when the 
scleractinians were abundant, including today, sponges were a very 
minor element in the construction of reefs. It is only before the 
corals first become abundant (before the Silurian) , and also dur- 
ing the interval between the decline of the Paleozoic corals and 
the rise of the Scleractinians (Permian and Triassic) , that spon- 
ges were important reef builders. This statement leaves out the 
stromatoporoid sponges, which managed to coexist with the Paleo- 
zoic corals through the Silurian and Devonian, though often in 
different reefs, and presumably in different environments. The 
bryozoans show a similar relationship to the corals but seem to 
have been sturdier competitors than the sponges. Bryozoa are 
still present in Silurian reefs alongside corals and stromatopor- 
oids, though they tend to be replaced by the latter in ecologic 
successions (Lowenstam, 1957). In Devonian times bryozoans are 



kk7 



rarely present in reefs, but reappear in the Carboniferous and 
Permian (Zechstein of Germany) when corals declined. 

The Ordovician reef-sponges are of interest in that they 
are siliceous (lithistid demosponqes) rather than calcareous (al- 
though frequently calcified diagenetically ) . They first appear 
( Archaeoscyphia ) in dominantly-algal early Ordovician mounds 
(Toomey , 19/0) ^but become more abundant and diversified in Middle 
Ordovician (Chazy and Black River) reefs, which is the only time 
during the Paleozoic that siliceous sponges were significant frame 
builders. This time coincides with the first radiation of the 
lithistid demosponges. It may be that the higher rate at which 
stromatoporoids , corals and bryozoa could secrete calcium carbon- 
ate skeletons was the reason for the near disappearance of lithi- 
stids from the later reefs. When the corals declined at the end 
of the Paleozoic, it was the calcareous Sphinctozoan sponges that 
replaced them as important reef-builders , in Permian and Triassic 
times, along with the ever present calcareous algae. 

It should be noted that most lithistid sponges, although 
their skeletons are rigid, do not by themselves bind sediment or 
build up massive structures. In the Crown Point reefs sediment 
binding was probably carried on only by stromatoporoids, laminar 
bryozoa, corals, and calcareous algae. Nevertheless, the lithi- 
stids cover, on the average, from 22% to 50% of the surface of 
the reefs in which they are most abundant (Pitcher, 1964, p. 662, 
675) . They thus contributed significantly to the bulk of the 
reef mass. They also served to trap sediment. That this by it- 
self can be a potent factor in mound formation is indicated by 
the late Jurassic sponge "reefs" of Germany (Roll, 1934) in which 
siliceous sponges built mounds apparently solely by trapping sed- 
iment and without the significant presence of binding organisms. 
These Jurassic mounds are the only known examples of siliceous 
sponge reef-like structures in post- Paleozoic times. 

It is possible that some of the laminar Anthaspidella was 
actually of encrusting habit and may have helped to bind other 
skeletal material, but its role would have been minor compared to 
that of the more abundant binding organisms. 

ECOLOGIC SUCCESSION 

Ecologic succession in the Day Point reefs can hardly be 
said to exist, since the reefs consist only of one species of bry- 
ozoan. The encrusting of the coral Lamottia by the bryozoan Bat - 
ostoma is probaUaly not true succession if the corals are not in 
place. It is worth noting, however, that the Lamottia bed is im- 
mediately succeeded by Batostoma reefs which were built on the 
coral debris (Pitcher, 1964, p. 650) as shown by cores. 



kk8 



In the more complex Crown Point reefs no clear succession 
is evident though there are suggestions of it. The stromatopor- 
oid Pseudostylodictyon frequently forms small reef lets by itself, 
resting on pelmatozoan calcarenite. It also often forms the 
basal parts of larger reefs, together with subordinate ramose 
bryozoa. Subsequently there succeeds a more diverse fauna of the 
lithistid sponges Zittelella and Anthaspidella , the coral Billing- 
saria, the bryozoan Batostoma and a flora of Sphaerocodinium 
and Solenopora . Some reefs on Valcour Island end with this com- 
munity. Others on Isle La Motte often have a capping of Pseudo - 
stylodictyon alone. In this mature reef community the lithistid 
sponges and the stromatoporoids occupy by far the largest surface 
area. Billingsaria , bryozoans and the algae are distinctly subor- 
dinate. The stromatoporoids can be considered to form a pioneer 
community which initiates reef development. It apparently pro- 
vides a favorable substrate for the lithistid sponges and for the 
encrusting corals, bryozoans and algae. The lithistid sponges 
( Zittelella , Anthaspidella ) can be quite common in the calcarenites 
away from the reefs, and therefore do not need the stromatoporoids 
as a base. Their participation in the reef is facultative rather 
than obligatory. The development of this rudimentary succession 
may be a matter of building up into somewhat shallower water, as 
is suggested by the change from raunose to laminar algae. It may 
also be a matter of the development of a firmer substrate than is 
provided by the surrounding shell sand. Biotic factors such as 
the availability of food probcibly also enter into the picture. 
Laminar algae, favored in their growth by a hard substrate, may 
attract herbiverous meiobenthos, which may in turn provide cibun- 
dant food for Billtngsaria , and indirectly, more bacteria for the 
sponges. 

In the Chazyan mounds of Quebec, a better-defined ecologic 
succession has been ascertained (see Toomey and Finks, 1969). 
Here pioneer communities of the encrusting bryozoan Batostoma are 
succeeded by a mixed bryozoan-coral community ( Batostoma , Chazy - 
dictya , Billingsaria , Eof letcheria ) . Finally the corals ( Billing - 
saria or Eofletcheria ) become dominant over the bryozoans at the 
top of the mound, perhaps a foretaste of things to come. 

COMPETITION 

Bryozoans tend to show a somewhat inverse relationship of 
abundance with reference to stromatoporoids and sponges (Pitcher, 
1964, figure 44) suggesting competition, as might be expected 
from the fact that they are all suspension feeders. At the top 
of the Crown Point, bryozoan reefs occur side by side with stroma- 
toporoid-lithistid reefs. They tend to dominate the Valcour reefs 
again, almost as they did in the earlier Day Point. The variabil- 
ity of the proportions of reef organisms in the Crown Point from 
one reef to the next, also suggests that there was near-equality 



449 



in competition between many of these organisms. At least one reef 
in the pasture on Isle La Motte is composed of 50% Billingsaria 
throughout (Pitcher, 1964, p. 666). Other reefs in the same pas- 
ture contain, on the surface, anyway, about 50% lithistid sponges 
( Zittelella, Anthaspidella ) . The corals and the sponges did not 
compete for food but they probably competed for substrate space. 
Occurrences of Billingsaria and Zittelella together on the flanks 
of reefs in this same pasture indicate that they had the same en- 
vironmental tolerances. 



VERTICAL ZONATION 

In the early Day Point bryozoan mounds, the mounds are built 
of laminar Batostoma or Cheiloporella , while the interreef areas 
contain abundant branching Atactotoechus . This may be considered 
a rudimentary sort of depth zonation, with the branching bryozoa 
occupying the deeper quieter water, and the laminar bryozoa the 
rougher shallower zones. However, the total relief at any one 
time was scarcely more than a foot or two (see Pitcher, 1964, fig- 
ure 10) and the differences in wave energy could not have been 
very great. Nevertheless, the presence of branching bryozoa, a- 
long with stromatoporoids , in the basal parts of Crown Point reefs, 
and their replacement by laminar bryozoa higher up (Pitcher, 1964, 
figure 8) suggests that there may be something to this form distri- 
bution in relation to depth. Certainly in living sponges, corals, 
and bryozoa there is a similar confinement of branching forms to 
the less rough water areas. 

The surface distribution of organisms on a Crown Point mound 
was studied by Pitcher (1964, figure 26) from the low flanks up to 
its crest. This should reflect bathymetric differences. He found 
that the stromatoporoids were most abundant at the crest, the bry- 
ozoa most abundant somewhat lower down, and the corals and lithis- 
tid sponges most abundant still lower on the flanks with the spon- 
ges remaining a±>undant further down than the corals. This again 
would correspond to a well-known pattern of morphological distri- 
bution, with the conical or cup-shaped lithistids ( Zittelella) 
being characteristic of quieter, deeper water, while the laminar 
bryozoans, corals and stromatoporoids are characteristic of rough- 
er water. The total vertical relief involved is scarcely six feet, 
and except for the absence of stromatoporoids at the base and the 
absence of lithistids and bryozoa on the crest, all the forms oc- 
cur over the whole reef. Thus the environmental differences can- 
not have been very great. 

A more pronounced bathymetric differentiation may be shown 
by some of the Crown Point reefs on the southwest shore of Valcour 
Island, on the point of land north of the concrete boat dock. 
Here the flanking beds pass laterally into dark calcilutites with 
numerous hexactinellid sponge root-tufts and body fragments. These 



450 



are much more delicate sponges and may have occupied a depressed 
area with genuinely quiet water peripheral to the reef. 

ORIENTATION AND CURRENTS 

Bryozoan mounds in the Day Point (Pitcher, 1964, figure 19) 
and stromatoporoid reeflets in the Crown Point (on both Isle La 
Motte in the Goodsell Quarry, and on the mainland at Sheldon Lane) 
tend to have a roughly north-south orientation. This is parallel 
to the paleoshore, and the mounds may have grown either in belts of 
optimum depth or into the set of longshore currents. An indication 
that currents may be involved is shown by the fact that hexactinel- 
lid sponge root-tufts in non-reefy beds of the Crown Point at South 
Hero, Vermont (Pitcher, 1964, figure 32) show the same preferred 
orientation on the bedding planes. Orthocone nautiloid shells are 
less clearly oriented, but in the channels that cut the Crown Point 
reefs, nautiloid shells are most commonly oriented parallel to the 
axis of the channel, obviously parallel to currents sweeping 
through. Maclurites shells are also often piled together in pock- 
ets in these channels, probably as a result of current action. The 
channels, however, may not be strictly contemporary with the reefs 
they cut, 

CHANNELS 

The Crown Point reefs are cut by numerous channels, mostly 
one to three feet wide and as much as two feet deep, filled with a 
black calcarenite that contrasts sharply with the light calcilutite 
of the reef rock. There is a considerable body of evidence that 
these channels may have been formed subaerially by solution, orig- 
inally pointed out by Oxley and Kay (1959, p. 831), possibly by en- 
largement of tectonic joints, following consolidation and diagene- 
sis of the reef rock. The entire sequence of events would have to 
have tciken place entirely within Crown Point time, perhaps several 
times. The evidence is as follows: 

1. The channels have sharp boundaries against the reef 
rock along smooth surfaces that cut through the middle 
of stromatoporoid colonies, lithistid sponges, and cal- 
cilutite matrix in a continuous sweep. The matrix must 
have been consolidated, and the lithistid sponges may 
have already been changed from silica to calcite, for 
they show no effects of differential hardness on the 
erosion surface. 

2. The channels usually end in rounded culs-de-sac, or 
sometimes have an ovoid shape, suggesting either pot- 
hole-like abrasion or sinkhole-like solution. There 
are agsentially no quartz clasts in the surrounding sed- 
iments, so that abrasion would seem to be unlikely, 
thus leaving solution as the alternative. 



451 



3. The channels tend to intersect at close to right angles 
and most frequently, though by no means universally, 
are oriented roughly north-south and east-west. This 
suggests that they may follow a tectonic joint pattern. 
Participants in the trip are invited to compare the 
form of the channels with that of solution-enlarged 
joints now being eroded in the same rock. 

4. If the channels were surge channels present in the act- 
ive reef, we would expect to find them bordered with at 
least some entire outlines of reef-building organisms, 
or where these were broken by contemporary wave- action, 
to find the broken outlines, and margins of the channel 
as a whole, to be irregular rather than smooth. 

Because the calcarenite filling the channels contains Crown 
Point guide fossils identical to those beneath and to either side 
of the reef, and because such channeled reefs occur at more than 
one level within the Crown Point beds in the same area, we must 
assume that the entire process postulated took place repeatedly 
within Crown Point time. If Crown Point time is assumed to be one- 
third of Chazy time, and that one-sixth of Ordovician time and Or- 
dovician time to be 60 million years long, then we have 3.3 million 
years for these processes to take place in. Admittedly, this may 
be hard to swallow, and we have not had the opportunity to test 
the hypothesis adequately, but participants in the field trip may 
wish to think about these possibilities while examining the out- 
crops. Gavish and Friedman (1969) have recently demonstrated post- 
glacial (within 10,000 years) calcification of quartz sand grains 
during consolidation of later glacial eolianites under subaerial 
conditions, thus providing strong support to this hypothesis. On 
the other hand there are elongate calcilutite-f illed pockets, of- 
ten containing numerous large nautiloid shells, that occur within 
the reef mounds of both Crown Point and Valcour. These may have 
been channels contemporaneous with the reefs. In some, algal 
coatings cover the shells and also line the walls of the pockets 
(see Goodsell Quarry, for example), 

ITINERARY 

The walking tour will start at the north end of the picnic 
ground and trailer camp on the north side of Wait Bay in south- 
eastern Isle La Motte. It may be reached by following the main 
north-south road down the center of Isle La Motte to its southern 
end, turning left (east) to the trailer park entrance, and then 
turning left (north) up the hill to the picnic ground. Please 
note that the entire trip is on private property, and that per- 
mission must be secured from the landowners for visits. 

Cross the fence and walk north to the bare exposures of the 



^52 



Lamottia biostrome in the Fleury Member of the Day Point Formation. 
CAUTION ! DO NOT STEP INTO SOLUTION-ENLARGED JOINTS. SOME ARE 
PARTLY CONCEALED BY VEGETATION. WALK ONLY ON BARE ROCK SURFACES. 
THE JOINTS ARE OVER A FOOT DEEP. 

The hemispherical to discoidal heads of Lamottia are closely 
packed in a calcarenite matrix. Joints offer an opportunity to 
observe their orientation in section. More than half are over- 
turned over much of the area. Many are broken. The proportion of 
broken ones increases to the north and east, where the biostrome 
passes into calcarenite with ever fewer and smaller fragments of 
Lamottia. In the central area of the exposure there are belts 
some 10 feet wide in which fragmentation, proportion of overturned 
specimens, and quantity of calcarenite matrix, are higher than 
elsewhere. These may represent surge channels. In the peripheral 
area to the northeast one may see much laminar Batostoma chazyensis 
surrounding the Lamottia fragments. 

This is the type locality for the genus Leimottia Raymond 
(1924). Although Raymond's description of this bed as the "world's 
oldest coral reef" may be disputed, it still seems to be unchal- 
lenged as the world's oldest occurrence of corals of any kind. 

Walk northwestward upsection, so far as fence lines, culti- 
vated fields and vegetation permit. DO NOT DISTURB FENCES OR LEAVE 
GATES OPEN ! NO SMOKING WHILE WALKING THROUGH THE FIELDS; THERE IS 
A DANGER OF FIRE. ALSO, PLEASE KEEP OFF CULTIVATED GROUND. 

About 1400 feet to the west are circular mounds of laminar 
Batostoma chazyensis containing small sponges near their periphery 
as well as cystoids in place throughout. These mounds (see Plate 
1) immediately overlie the Lamottia bed. Another 1000 feet to the 
north' brings us to elongate mounds (aligned N-S) of branching bry- 
ozoa at the very top of the Day Point Formation. This may repre- 
sent deeper water. 

Continue to walk northward to a small dirt road, then walk 
west along it to a T-junction with a larger dirt road. Turn left 
and follow it southwest to a house and barn on the right. We will 
enter a gate into the large pasture behind the house and barn. Mr. 
Ira LaBombard, the present owner of the property, has kindly given 
us permission to enter his pasture to study the reefs in the Crown 
Point and lower Valcour Formations. He has requested, as a condi- 
tion of this permission, that NO SPECIMENS WHATEVER be collected. 
PLEASE RESPECT THIS ORDER !!! We will have an opportunity later 
in the day to collect from these same beds at another locality. 
The fossils are so beautifully displayed here that relationships 
may be seen without disturbing the rock. They may be photographed 
very advantageously on the glacially polished surfaces. 

The reefs exposed here are mainly in the Crown Point Forma- 
tion and are the ones intensively studied by Pitcher (1964), 



^53 



You may examine contemporaneous reefs by walking northeastward 
along strike. You may examine younger reefs by walking northwest- 
ward upsection (dip is about 10 degrees NW) . 

The reefs are exposed as mounds of light rock. The calcar- 
enite between the reefs, and filling the channels in the reefs, is 
nearly black. The reefs outcropping nearest the fence were mapped 
by Pitcher as his assemblage A, consisting of the stromatoporoid 
Cystostroma and the alga Solenopora . Those beyond to the north- 
west"^ and covering most of the pasture up to a distinct linear 
rise in the ground, belong to Pitcher's assemblage B. These show 
interesting variations from reef to reef as well as changes in 
faunal distribution from flanks to tops of the mounds. The fauna 
consists of the stromatoporoid Pseudosty Iodic tyon eatoni , the lith- 
istid demosponges Zittelella varians and AnthaspTdella sp. , the 
tabulate coral Billingsaria "parva , the bryozoan Batostoma chazyen - 
sis , and the calcareous algae Solenopora , SphaerocodiniUm and Gif- 
vanella . 

The fossils may be identified readily on weathered surfaces 
as follows: 

1. Pseudosty lodictyon eatoni: Large whitish masses with 
fine dark laminae forming concentric patterns about centers an 
inch or two apart. These concentric patterns represent the mame- 
lons and their small size is characteristic of the species. 

2. Zittelella varians : Circular, dark gray bodies two to 
three inches in diameter, with a central circular light area rep- 
resenting the matrix-filled cloaca, and radial light areas, or 
ovoid dots, a few millimeters wide, representing the canals. In 
longitudinal section, the sponge is conical, and oblique sections 
will show the expected intermediate shapes. Some specimens have 
an irregular outline in cross section. 

3. Anthaspidella sp: Similar to Zittelella in color and 
texture, but shaped like long sinuous bodies , and inch or so thick 
and several inches long, when seen in cross section. A surface 
view of the sheet-like sponge shows a somewhat irregular mass with- 
out a cloaca. The complete sponge has a short stalk, the whole 
being shaped somewhat like a distorted cake-plate. The open 'spon- 
gy' texture may help when shape fails. Needless to say, the shape 
and geometric arrangement of the spicules in thin section is nec- 
essary for a secure identification. Not every shapeless mass is a 
sponge. 

4. Billingsaria parva: Small, black, oval patches, a few 
inches across. The dark color is very distinctive. Close inspec- 
tion with a hand lens will reveal the stellate outlines of the cor- 
alites with their characteristic septal ridges. 



i^5^ 



5. Bryozoa: These weather white, either as small branching 
twiglets, or as laminated sheets. Identification requires thin- 
sections, but the outlines of the zooecia are usually visible on 
the weathered surface and suffice to identify it as a bryozoan. 

6. Solenopora ; White concentric circles, often sparry. A 
few inches across. This is the most common form of Solenopora 
seen on the reef surfaces. 

7. Girvanella ; Small black ovoid bodies, less than an inch 
in length. These are oncolites, or algal-coated shell fragments. 

8. Maclurites magnus ; Large coiled shells a few to several 
inches across. No septa. The shell substance is white in cross- 
section. 

At the rise in ground is a one-foot stromatolitic layer with 
many orthocone cephalopods. Pitcher called this his assemblage C 
and assumed it was laid down as a blanket during a relative drop 
in sea level. It forms a dip slope through which appear, apparent- 
ly, the tops of assemblage B mounds, as well as small mounds of 
Batostoma chazyensis alone which Pitcher called assemblage D. At 
the west end of this cuesta-like feature, nearest the main road, a 
good cross-section of an assemblage B mound is exposed (see Plate 
2). 

Down the dip slope, above a ten- foot interval of grey cal- 
carenites, are mounds in the lower part of the Valcour Formation. 
They are composed of Batostoma campensis , together with the alga 
Solenopora . Some Zittelella may be found. The bryozoa are clear- 
ly dominant. 

Walk northeastward along strike for about a half-mile, ob- 
serving Crown Point mounds as you go. You will eventually reach 
the Goodse.ll Quarry, operated by the Vermont Marble Company. The 
quarry is opened in the lower beds of the Crown Point which are 
relatively lacking in reefs except for small stromatoporoid-algae 
mounds. The quarry has been intermittently active, and the stone, 
which makes a beautiful black marble when polished, has been wide- 
ly used as an interior trim. The rock weathers light gray, and 
has also been locally used as a dimension stone. It was used to 
build the old fort. Fort Montgomery, visible from the Rouses Point 
Bridge. 

CAREFULLY avoiding falling into the water- filled quarry, one 
may observe vertical sections through stromatoporoid-algal mounds 
and their relationships with the surrounding calcarenite (see Plate 
5) . By tracing laminae from the mounds into the surrounding sedi- 
ment, one can see that the mounds never stood more than a foot or 
two above the sea floor at any one time, though the total thickness 
is much greater because of the persistence of the mound population 



455 



on the saune spot. On the quarry benches, especially the glacial- 
ly polished upper surface, one may see plain views of mounds and 
note their tendency to a N-S lineation. On these surfaces also, 
especially when wet down, one may see orthocone and other nauti- 
loid shells, and Maclurites shells, overgrown by algal coatings. 



ACKNOWLEDGEMENTS 

We wish to thank Mrs. Malvina Bruley and Mr. Ira LaBombard 
of Isle La Motte, for permission to visit the classic exposures 
on their respective properties. Their cooperation has made this 
excursion possible. R. M. Finks extends special thanks to Mr. 
Rodney V. Balasz for information concerning possible channels in 
the Lamottia biostrome, and to his paleontology class for mapping 
some of the channels in the various reefs in the fall of 1968. 



BIBLIOGRAPHY 

Gavish, E. and Friedman, G. M. (1969) Progressive diagenesis in 
Quaternary to Late Tertiary carbonate sediments: sequence and 
time scale: Jour. Sed. Pet., v. 39, p. 980-1006. 

Hartman, W. F. and Goreau, T. F. (1970) Jamaican coralline sponges 
their morphology, ecology and fossil relatives in: Fry, W. G. 
(ed.) Biology of the Porifera, Sympos. 25, Zool. Soc. London, 
p. 205-243. 

Lowenstcun, H. A. (1957) Niagaran reefs in the Great Lakes area in ; 
Ladd, H. S. (ed. ) Treatise on marine ecology and paleoecology , 
V. 2, Paleoecology: Geol. Soc. America, Mem. 67, p. 215-248. 

Odum, E. P. (1959) Fundamentals of Ecology, 2nd ed. , Wiley, New 
York. 

Oxley, P. and Kay, M. (1959) Ordovician Chazyan Series of Cham- 
plain Valley, New York and Vermont, and its reefs: Bull. Amer- 
iccui Assoc. Petrol. Geol., v. 43, p. 817-853. 

Pitcher, Max (1964) Evolution of Chazyan (Ordovician) reefs of 

eastern United States and Canada: Bull. Canadian Petrol. Geol., 
V. 12, p. 632-691. 

Rasmont, R. (1968) Nutrition and digestion in: Florkin, M, and 
Scheer, B. T. , Chemical Zoology, V. II, Porifera, Coelenterata 
and Platyhelminthes, p. 43-51. 

Raymond, P. E. (1924) The oldest coral ree.. : Vermont State Geol- 
ogist, 14th Report, p. 72-76. 



456 

Roll, A. (1934) Form, Bau and Entstehung der Schwammstotzen im 
silddeutschen Malm; Palaeontol. Zeitschr. , v. 16, p. 197-246. 

Sieber, R. (1937) Neue Untersuchungen uber die Stratigraphie und 
Oekologie der Alpinen Triasfaunen. 1. Die Fauna der nordalpin- 
en Rhatrif fkalke, Neues Jahrb. , Beilage Band, v. 78, pt. B, 
p. 123-187. 

Toomey, D. F. (19 70) An unhurried look at a Lower Ordovician mound 
horizon. Southern Franklin Mountains, West Texas: Jour. Sed. 
Pet., V. 40, p. 1318-1334. 



GOO0SELL^„„^ (J) ,. 




GEOLOGIC AND LOCALITY MAP 
OF SOUTHEASTERN ISLE LAMOTTE.VT 



Figure 1. Geologic and locality map of 
Southeastern Isle La Motte, 
Vermont. After Pitcher, 1964. 



457 



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^58 




Figure 3o Map showing composition of several 
reef assemblages in LaBombard's pasture, 
Isle La Motte. Vermont. (from Pitcher, 196^) 




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^60 



PLATE 1 



Figure 1 Outcrop photograph of the surface of a Middle 
Ordovician (Chazyan) bryozoan mound exposed in 
the Day Point Formation (uppermost Fleury Member) 
on Isle La Motte, western Vermont. Note general 
lineation of the bryozoan colonies and included 
round sponges; length of hammer approximately 14 
inches . 

Figure 2 Thin section photomicrograph (X3) of characteris- 
tic bryozoan mound rock that forms conspicuous 
mounds in the uppermost Day Point Formation, 
Fleury Member, on Isle La Motte, western Vermont. 
The mound rock is primarily composed of consecu- 
tive sheets or layers of the colonial trepostome 
Batostoma chazyensis Ross , separated by lime mud 
layers containing relatively abundant, although 
quite small, dolomite rhombs (small grey flecks). 



i^62 



PLATE 2 



Outcrop photograph of a series of typically small-sized 
Crownpointian (Middle Ordovician - Chazyan) mounds ex- 
posed in LaBombard's pasture. Isle La Motte, western 
Vermont. Rounded mound structures are composed of lime 
mud containing abundant algae, sponges, stromatoporoids 
and trepostome bryozoans. The beds filling in the sur- 
face irregularities and capping the mounds are dominant- 
ly composed of relatively coarse-textured pelmatozoan 
debris (see Plates 3 and 4) . The length of the sledge 
hammer located on the right hand side of the prominent 
mound is approximately 3 feet. 



I 




m^ 



46^ 



PLATE 3 



Figure 1 Thin section photomicrograph (X3) of a transverse 
cut through the sponge Zittelella in what is typ- 
ically Crownpointian mound rock; LaBombard's pas- 
ture, Isle La Motte, western Vermont. Note over- 
all muddy character of the rock, and the appear- 
ance of an encrusting bryozoan ? on the outer 
surface of the sponge. 

Figure 2 Thin section photomicrograph (X14) of Crownpoint- 
ian mound rock with relatively abundant encrusting 
(bead-like segments) algae of the genus Sphaero- 
codium; LaBombard's pasture. Isle La Motte , west- 
ern Vermont. Again, note the dominant ly muddy 
character of the rock. Scattered small grey 
flecks are floating dolomite rhombs. 



466 



PLATE 4 



Figure 1 Outcrop photograph of a channel cutting mound 
rock in the Middle Ordovician (Chazyan) Crown 
Point Formation, west of the Goodsell Quarry, 
Isle La Motte, western Vermont. The width of 
the channel is approximately 18 inches. Note 
lighter colored mound rock on either side of 
darker-colored channel rock. 

Figure 2 Thin section photomicrograph (X4) of channel 

rock from the above locality. Rock is primar- 
ily a pelmatozoan calcarenite, although intra- 
clasts (small rounded dark grains) , bryozoan 
and brachiopod fragments are also present. 
Cavities or original void spaces filled with 
secondary granular sparry calcite are also 
common within the channel rock. 



J^68 



PLATE 5 



Figure 1 Stromatoporoid ( Ps eudos ty lodi ctyon ?) mound 
exposed on the south wall of Goodsell Quarry 
(June, 1962); Middle Ordovician (Chazyan) Crown 
Point Formation, Isle La Motte , western Vermont, 
Stromatoporoid mound is approximately 4 feet in 
width and 2 1/2 feet in height. 

Figure 2 Thin section photomicrograph (X4) of a vertical 
section of the stromatoporoid Pseudostylodicty- 
on ? chazianum (Seely) from the lower part of 
the Crown Point Formation, LaBombard's pasture. 
Isle La Motte, western Vermont. Specimen shows 
characteristic thin laminae separated by pro- 
nounced layers of lime mud. 

Figure 3 Thin section photograph (X4) of a horizontal 

section of the stromatoporoid Pseudostylodicty- 
on ? eatoni (Seely) showing mamelons of various 
iTzes , from the lower part of the Crown Point 
Formation, LaBombard's pasture. Isle La Motte, 
western Vermont. 



470 



PLATE 6 



Figure 1 Thin-section photomicrograph (X8) of a pelmato- 
zoan grainstone from a channel associated with 
the Lamottia buildup (" Lamottia reef" of Ray- 
mondTT Day Point Formation (Chazyan) middle 
Fleury Member, Isle La Motte, western Vermont. 
Note abundance of pelmatozoan ossicles (proba- 
bly cystoid and/or blastoid) , and the dominant 
sparry calcite matrix; many of the pelmatozoan 
ossicles have calcite overgrowths. The small 
black grains are intraclasts and/or Girvanella 
pellets (diagnostic structures not seen at this 
magnification) . 

Figure 2 Outcrop photograph of the Lamottia accumulation 
( " Lamottia reef") located near the center of the 
buildup. Note the jumbled mass of coral "heads" 
which appear to be heaped together and overturn- 
ed, probably due to wave and/or current sorting. 
Length of hammer is 11 inches; Day Point Forma- 
tion, middle Fleury Member, southeastern Isle 
La Motte, western Vermont. 

Figure 3 Thin-section photomicrograph (X4) of the muddy 

rock matrix between the massive Lamottia "heads", 
Rock can be classified as a skeletal wackestone. 
Note large fragment of the tabulate coral Lamot- 
tia heroensis Raymond set within a muddy matrix 
with included intraclasts and abundant skeletal 
debris. Thin-section taken from rock near the 
center of Raymond's "oldest coral reef" within 
the Day Point Formation, middle Fleury Member, 
southeastern Isle La Motte, western Vermont. 



473 



Trip P-2 

CAMBRIAN FOSSIL LOCALITIES IN NORTHVJESTERN VERMONT 

George Theokritoff 

Rutgers University 
Newark, New Jersey 

INTRODUCTION 

The Cambrian sections of northwestern Vermont are 
widely regarded as classic on account of the discovery there- 
in of Cambrian fossils by Zadock Thompson and S.R. Hall in 
1847 and Noah Parker in 1954, as well as on account of the 
variety of the fossils subsequently collected. The first 
fossils found were described by Elkanah Billings and James 
Hall. Further discoveries were made by Charles Walcott, 
More recent paleontological work includes that of Clark 
and Shaw (1968a; 1968b), Howell (1937). Kindle and Tasch 
(1948), Rasetti (1946), Raymond (1924{ 1937), Resser and 
Howell (1938), Schuchert (1937), Shaw (1951-1966), and 
Tasch (1949). 

Recent regional syntheses (Cady, I968J Palmer, 1971; 
Rodgers, I968; Theokritoff, I968) have interpreted the Cam- 
brian rocks of northwestern Vermont as representing, on the 
one hand, the deposits of a sand-carbonate shelf extending 
to the west and northwest onto the craton and, on the other 
hand, the deposits of a deeper water basin situated to the 
east and southeast. The sand-carbonate shelf formed a 
steep bank, rising above the basin and contributing carbonate 
clasts to sites of dominantly shale deposition at the foot 
of this sand-carbonate bank. The boundary between the shelf 
facies and the basin facies is now complicated by and partly 
obscured by thrusting. 

The present trip will visit three fossil localities. 
The first locality is in the Lower Cambrian Monkton Quartz ite, 
the second in the Lower Cambrian lower Parker Shale, and the 
third in the Upper Cambrian Gorge Formation. The first and 
the third are in the shelf facies, the second in the basin 
facies. 

It is a distinct pleasure to acknowledge the court- 
esy of the three gentlemen, owners of private land, who have 
graciously granted us permission to enter their property: 
Mr. Oscar Baker of Highgate Falls, Mr, Euclide Duhamel of 
Swanton, and Mr. Louis Gregoire of Mallett's Bay. 



47^ 



DESCRIPTION OF OUTCROPS AND ROAD LOG 

7i* Topographic Quadrangle Mapsi St. Albans (Vt, ) and Mil- 
ton (Vt.T 

Start from Perkins Geology Hall, UVM, 
Proceed to Interstate 89 north to Exit 17 (Cham- 
plain Islands), 
Exit for Route 2 West, 

Mileage 

00,0 Enter Route 2 West, 

00.7 Cedar Hill Gift Sbappe on left. Park cars at 
gift shop and walk to top of hill to the south, 
Fossiliferous outcrops are beneath power-line. 

Stop 1 - The rock exposed here is a coarse gray -buff to tan 
weathering gray sandstone. It is referred to as the Monkton 
Quartz ite. Abundant fossils may be found on weathered sur- 
faces. At this locality, the commonest fossils are trilo- 
bite fragments, mostly disarticulated thoracic segments, 
but recognizable olenellid cephala, probably of Olenellus . 
and dorypygid cranidia and pydidia, probably of Bonnia . 
also occur. The fossils are preserved as molds in the sand- 
stone matrix. All are disarticulated but not badly abraded 1 
these circumstances suggest sedimentation and burial in 
gently moving water. The Monkton Quartz ite probably re- 
presents a strand-line deposit. 

The first systematic description of the fossils 
from this locality is that of Kindle and Tasch (19^8), 
Further descriptions, with some taxonomic revisions, were 
published by Shaw (I962), 

Return to Interstate 89. 

01,^ Take Interstate 89 north to Exit 21 (Swanton), 
Approximately 25 miles, 

00,0 Enter Route 78 West to Swanton* 

01,0 Turn left (south) onto Route 7 in Village of 
Swanton, 

02.0 Cross bridge over Missisquoi River, 

03,9 Turn left just south of farmhouse on left of high- 
way. Enter lane through gate. The Kelly quarry is _ 
just south of this lane approximately 0,1 miles ■ 
east of the gate, ^ 



^75 



Stop 2 - The Kelly quarry, described by Schuchert (1937* 
p. 1035) and Shaw (195^» p. 10^1), exposes two rock types 
in the lower Parker Slate, The lower of these is a dark-green- 
ish-gray weathering gray-green micaceous slate with some 
interbeds of buff weathering gray laminated fine to medium 
grained sandstone. Dolomite nodules occur near the top. 
The upper rock type is a tan-buff weathering light gray 
dolomite, exposed on top of the knoll above and to the 
east of the quarry face. 

Poorly preserved trilobite fragments may be found 
in the slate; fragments and external molds of Kootenia 
are fairly common in the overlying dolomite. Shaw (195^» 
p. 1041) gave a check list for both horizons. 

Dactyloidites asteroides has been reported by 
Schuchert (1937, p. 1035) and Shaw (195^. p. 104l) from the 
slates at the entrance to the quarry. Shaw (1955. p. 784) 
reported a somewhat different form, D. edsoni, from the 
same locality. Dactyloidites has been described and figured 
by Ruedemann (1934, p. 28-30, plates 4-6) who thought it 
was probably algal, D. edsoni was also described by Resser 
and Howell (1938, p. 210) who thought it was algal, Walcott 
(1998) thought Dacty loidites was a scryphozoan medusa, 
Hantzschel (1962, p. W240) and Harrington and Moore (1956, 
p, FI59) consider Dactyloidites to be an unrecognizable form. 

Return to Route 7 north, 

04, 3 Turn right (east) on paved road, 

05,6 Stop sign. Turn left (north). 

08.3 Turn left (just before steel bridge over Missis- 
quoi River at Highgate Falls) and drive through 
Swanton Municipal Power plant property to private 
property owned by Mr. Oscar Baker. Follow the 
lane to the right and park cars by river. Outcrops 
are to the east. 

Stop 2. - ^^ contrast to the first two stops, the last is 
dominated by carbonates. This section in the Highgate 
gorge has been described by Raymond (1924, p. 459 )» Schu- 
chert (1933. p. 373-377} 1937, p. IO67-IO69), and in greater 
detail by Shaw and Clark (I968). 

Schuchert (1937, p. IO7O) interpreted a thick 
breccia in the gorge as a thrust breccia and hence recog- 
nized two formations here, separated by this inferred thrust. 
The upper he referred to the Highgate Formation and the lower 
to the Gorge Formation. Shaw (in Shaw and Clark, I968, p. 381) 
did not recognize a thrust in this part of the section, 



^76 



interpreting the breccia in question as debris from a sub- 
marine land slide, and hence he assigned to the Gorge Forma- 
tion the strata that Schuchert had referred to the Highgate 
Formation here. 

Several fossiliferous horizons have been noted in 
the gorge section but the faunas of only some have been 
described. Clark and Shaw (1968a; 1968b) described the 
trilobites from bed 3f which is exposed downstream from the 
most v;esterly vertical cliff. This bed has yielded two 
distinct faunas, a lower referred by Clark and Shaw (1968a) 
and Palmer (1971, p. 176) to the late Dresbachian Dunder - 
bergia zone, and an upper correlated by Clark and Shaw 
(1968b) with the Hungaia magnifica fauna, known from boulders 
in Quebec and western Newfoundland (Whittington, I966, 
p, 701). Palmer (1971) referred the upper fauna in bed 
3 to the late Franc onian. 

Higher strata have yielded fossils from a number 
of horizons. The lowest of these is stratigraphically about 
a foot above bed 3 and is exposed only in the same general 
locality as bed 3. Its trilobites have been described by 
Raymond (1924j 1937). Other fossiliferous horizons have 
been identified by Shaw and Clark (I968) in the most westerly 
vertical cliff section and in the cliff section to the east, 
between the two rock dumps. The fossils from some of these 
have been described by Raymond (192^j 1937) and Rasetti 
(19^6), and have been correlated with the Hungaia magnifica 
fauna to be Trempealeauan and also correlative of the 
Early Tremadocian. 

00,0 Return to steel bridge at Highgate Falls, Cross 
bridge, 

00,^ Turn left in Highgate Center onto Route 78 west, 

04.6 Enter Interstate 89, 



REFERENCES CITED 

Cady, W.M., I968, The lateral transition from the miogeo- 

synclinal to the eugeosynclinal zone in northwestern 
New England and adjacent Quebec, p. I5I-I6I in 
Zen and others. Editors . Studies of Appalachian 
geology » northern and maritime: Interscience 
Publishers, New York, ^75 p. 

Clark, M.G., and Shaw, A.B., 1968a, Paleontology of north- 
western Vermont. XV, Trilobites of the Upper 
Cambrian Gorge Formation (upper bed 3)t Jour, 
Paleontology, v. kZ, p, 382-396, 



^ ( ( 



Clark, M.G., and Shaw, A.B,, 1968b, Paleontology of north- 
western Vermont, XVI, Trilobites of the Upper 
Cambrian Gorge Formation (upper bed 3)« Jour. 
Paleontology, v. /|2, p. 1014-1026. 

Hantzschel, Walter, I962, Trace fossils and Problematica 
p. W177-W245 in Koore, R.C., l^ditor . Treatise 
on Invertebrate Paleontology, v. W, Univ. Kansas 
Press, Lawrence, Kansas, 259 p. 

Harrington, H.J., and Moore, R.C., I956, Medusae Incertae 
Sedis and unrecognizable forms, p. F153-F161, 
in Moore, R.C,, Editor . Treatise on Invertebrate 
Paleontology, v. F, Univ. Kansas Press, Lawrence 
Kansas, 498 p. 

Howell, B.F., 193 7 I Cambrian Centropleura vermontensis 

fauna of northwestern Vermont: Geol. Soc. America 
Bull., V. i^8, p. 11^7-1210. 

Kindle, C.H,, and Tasch, Paul, 1948, Lower Cambrian fauna 
of the Monkton Formation of Vermont: Canadian 
Field-Naturalist, v. 62, p. »33-139. 

Palmer, A,R., 1971t The Cambrian of the Appalachian and 
eastern New England regions, eastern United 
States, p. 169-217, in Holland, C.H,, Editor . 
Cambrian of the New V/orld: Interscience Publishers, 
New York, 456 p. 

Rasetti, Franco, 1944, Upper Cambrian trilobites from the 
Levis conglomerate: Jour. Paleontology, v. 18, 
p. 229-258. 

Rasetti, Franco, 1946, Revision of some late Upper Cambrian 
trilobites from New York, Vermont, and Quebec: 
Am. Jour. Science, v. 244, p, 537-546, 

Raymond, P.E., 1924, New Upper Cambrian and Lowei Ordovician 
trilobites from Vermont: Boston Soc. Kat. Hist. 
Proc, v. 37, p. 389-^66. 

Raymond, P.E., 1937, Upper Cambrian and Lower Ordovician 
Trilobita and Ostracoda from Vermont: Geol. 
Soc. America Bull., v. 48, p. 1079-1146. 

Resser, C.E., and Howell, B.F,, 1938, Lower Cambrian Olenellus 
zone of the Appalachians: Geol. Soc. America Bull., 
V. 49, p. 195-248. 

Rodgers, John, I968, The eastern edge of the North American 
continent during the Cambrian and Early Ordovician, 
p. 141-149, in Zen and others. Editors , Studies 
of Appalachian geology: northern and maritime: 
Interscience Publishers, New York, 475 P» 



478 



Ruedemann, Rudolf, 193^. Paleozoic plankton of North 
America: Geol, Soc. America, Mem, 2, 1^1 p. 

Schuchert, Charles, 1933» Cambrian and Ordovician strati- 
graphy of northwestern Vermont: Am. Jour, Science, 
V. 231, p. 353-381. 

Schuchert, Charles, 1937 » Cambrian and Ordovician of north- 
western Vermont: Geol. Soc. America Bull., v. 48, 
p. 1001-1078. 

Shaw, A.B., 1954, Lower and lower Middle Cambrian faunal 
succession in northwestern Vermont: Geol. Soc, 
America Bull., v. 6^, p. 1033-1046. 

Shaw, A.B., 1955» Paleontology of northwestern Vermont. V. 
The Lower Cambrian fauna: Jour. Paleontology, 
V. 29, p. 775-805. 

Shaw, A.B., 1958, Stratigraphy and structure of the St, 
Albans area, northwestern Vermont: Geol. Soc. 
America Bull., v. 69, p. 519-567. 

Shaw, A.B., 1962, Paleontology of northwestern Vermont. IX. 

Fauna of the Monkton Quartzite: Jour. Paleontology, 
V. 36, p. 322-345. 

Shaw, A.B., and Clark, M.G., I968, Paleontology of north- 
western Vermont. XIV, Type section of the Upper 
Cambrian Gorge Formation: Jour. Paleontology, 
V. 42, p. 374-381. 

Tasch, Paul, 19^9 » A new fossil locality in the Lower 

Cambrian Monkton Formation of Vermont: Canadian 
Field-Naturalist, v. 63, p. 210-211, 

Theokritoff, George, I968, Cambrian biogeography and bio- 
stratigraphy in New England, p. 9-22 in Zen and 
others. Editors , Studies of Appalachian geology: 
northern and maritime: Interscience Publishers, 
New York, 475 p. 

Walcott, CD,, I898, Fossil medusae: U.S. Geol, Survey, 
Mem. 30, 101 p. 

Whittington, H.B., I966, Phylogeny and distribution of 

Ordovician trilobites: Jour. Paleontology, v. 40, 
p. 696-737. 



M-yy 



APPENDIX 



Vermont Geological Survey 
Publications 



All Vermont Geological Survey Publi- 
cations may be purchased through the Vermont 
Department of Libraries, Geological Publica- 
tions, Montpelier, Vermont 5 602. 

Please include payment with your or- 
der. Vermont residents must include 3% sales 
tax. 



480 



*** VERMONT GEOLOGICAL SURVEY BULLETINS *** 



1 Geology of the Bradf ord-Thetf ord Area, Orange County Vermont 

by Jarvis B. Hadiey, 1950 ^ 2.00 

2 Stratigraphy and structure of the Castleton Area, Vermont, by 

Ph i 1 ip" Fow ler, 1950 2.00 

3 Geology of the Memphremagog Ouadrangle and the Southeastern 
Portion of the Irasburg Quadrangle, Vermont, by Charles G. 

Dol I , 195 I 2.00 

4 A Study of Lakes in Northeastern Vermont, by John Ross Mills, 

1951 2.00 

5 The Green Mountain Ant i c I i nor i urn in the Vicinity of Rochester 

and East Middlebury, Vermont, by Philip Henry Osberg, 1952 2.00 

6 The Geology of the Rutland Area, Vermont, by W.F. Brace, 1953 2.00 

7 The Geology of the Bennington Area, Vermont, by John A. Mac- 
Fayden, 1956 2.00 



8 The Geology of the Lyndonville Area, Vermont, by John G. 
Dennis, 1956 



2.00 



9 The Geology of the Limestone of Isle LaHotte and South Hero 

island, Vermont, by Robert B. Erwin, 1957 2.00 

10 The Bed Rock Geology of the Ea?t Barre Area, Vermont by Varansi 
Rama Murthy, 1957 2.00 

11 The Geology of Concord, Waterford Area, Vermont by Eric and 
Dennis, 1958 2.00 

12 The Geology of the Mount Mansfield Ouadrangle, Vermont by 

Robert A. Christman, 1959 2.00 

13 The Geology of the St. Johnsbury Ouadrangle, Vermont and New 
Hampshire, by Leo M. Hall, 1959 2.00 

14 Bedrock Geology of the Central Champlain Valley of Vermont, by 
Charles W. Wei by , 1961 4.00 

15 Geology of the Camels Hump Quadrangle, Vermont by Robert A. 
Christman and Donald T. Secor, Jr., 1961 2.00 

16 Geology of the Plainfield Quadrangle, Vermont by Ronald H. 

Konig, 1961 2.00 

17 The Green Mountain Ant i c 1 i nor i um in the Vicinity of Wilmington 

and Woodford, Vermont, by James William Skehan, S.J., 1961 3.00 



*** VERMONT GEOLOGICAL SURVEY BULLETINS *** 



I 8 

19 
20 

21 

22 

23 



Geology of the Equinox Quadrangle and Vicinity, by Philip C. 
Hewitt, 1961 2.00 

The Glacial Geology of Vermont, by David P. Stewart, 1961 2.00 

Geology of the Island Pond Area, Vermont, by Bruce K. Good- 



win, 196 3 



2.00 



Bedrock Geology of the Randolph Quadrangle, Vermont, by Ernest 
Henry Ern, 1963 ^ 2.00 

Geology of the Lunenburg-Brunsw i ck-Gu i I dha I I Area, Vermont, 

by Warrenl. Johansson, 1963 2.00 



Geology of the Enosburg Area, Vermont, bv John G. Dennis, 
1964 



2.00 



24 Geology of the Hardwick Area, Vermont, by Ronald H. Kon i g 

and John G. Dennis, 1964 2.00 

25 Stratigraphy and Structure of a Portion of the Castleton Quad- 
rangle, Vermont, by E-an Zen, 1964 2.00 

26 Geology of the Milton Quadrangle, Vermont by Solon W. Stone 

and John G. Dennis, 1964 2.00 

27 Geology of the Vermont Portion of the Averill Quadrangle, by 

Paul Benton Myers, Jr., 1964 2.00 

28 Geology of the Burke Quadrangle, Vermont, by Bertram G. Wood- 
land, 1965 3.00 

29 Bedrock Geology of the Woodstock Quadrangle, Vermont by Ping 
Hs i Chang, Ernest H. Ern, Jr., and James B. Thompson, Jr., 

1965 2.00 

30 Bedrock Geology of the Pawlet Quadrangle, Vermont, by Robert 

C. Shumaker and James B. Thompson, Jr., 1967 2.00 

31 The Surficial Geology and Pleistocene History of Vermont, by 
David P. Stewart and Paul MacClintock, 1969 4.00 



482 



*** ECONOMIC GEOLOGY *** 



Economic Geology No. I - A Report on Magnetic Surveys of Uultrariia- 
fic Bodies in the Dover, Windham and Ludlow areas, Vermont, 
by Vincent J. Murphy, 1966 3.00* 

Economic Geology No. 2 - Report on a Resistivity Survey of the 

Monkton Kaolin Deposit and Drill Hole Exploration, by Jason 

A. Wark, 1968 3.00* 

Economic Geology No. 3 - Geology and Origin of the Kaolin at East 

Monkton, Vermont, by Duncan G. Ogden, 1969 3.00* 

Economic Geology No. 4 - Report on the Cutt i ngs v i I I e Pyrrhotite 

Deposit, Cutt i ngsv i I I e, Vermont, by Charles G. Doll, 1969 3.00* 

Economic Geology No. 5 - The Geology of the Elizabeth Mine, Vermont, 

by Peter F. Howard, 1969 3,00* 

Economic Geology No. 6 - Magnetic Surveys of Ultramafic Bodies in 
the Vicinity of Lowell, Vermont, by Vincent J. Murphy and 
Andrew V. Lacroix, 1969 3.00* 

Economic Geology No. 7 - Geochemical Investigations in Essex and 

Caledonia Counties, Vermont, by Raymond W. Grant, 1970 3.00* 

*** ENVIRONMENTAL GEOLOGY *** 

Environmental Geology No, I - Geology for Environmental Planning 

in the Barre-Montpe I i er Region, Vermont, by David P. Stewart, 

1971 2.00 

*** SPECIAL PUBLICATIONS *** 

Special Publication No. I - Paleontology of the Champlain Basin in 

Vermont, by Charles W, Welby, 1962 3.00 

Special Publication No. 2 - Mineral Collecting in Vermont, by R, W. 

Grant, 1968 3,00 

*** STUDIES IN VERMONT GEOLOGY *** 

Studies in Vermont Geology No. I - The Morphometry and Recent Sedi- 
mentation of Joe's Pond, Viest Danville, Vermont, by John S. 
Moore and Allen S. Hunt, 1970 2,00 



Studies in Vermont Geology No. 2 - Surficial Geology of the Brandon- 
Ticonderoga 15 Minute Quadrangles, Vermont, by G. Gordon Con- 



na I ly, 1970 



2.00 



483 



MAPS 



*** 



1 Topographic Map of Vermont, 1970, scale 1:250,000, contour 
i nterva I 100' 

2 Centennial Geologic Map of Vermont, 1961, scale 1:250,000 

3 Surficial Geologic Map of Vermont, 1970, Scale 1:250,000 

4 Generalized Geologic Map of Vermont, 1970, 8{ x II" - each 

In lots of 100 for schools - each 

5 Glacial Drift Sheets and Ice Directions - each 

In lots of 100 for schools - each 

6 Post Card Generalized Geologic Map of Vermont, 1970, 4 7/16 
X 6 7/15" 



2.00 
4.00 
4.00 

. 15 

. 10 

. 15 
. 10 

. 10 



7 Vermont Geological Quadrangle Maps - Areas Available: Castleton, 
Concord-Waterf ord , East Barre, Enosburg Falls, Equinox, 
Mt. Mansfield, Plainfield, Rutland, St. Johnsbury, Wilming- 
ton-V^oodf ord - each '25 

*** STATE PARKS *** 

Geology of Button Bay State Park, by Harry W. Dodge, Jr., 1962 .25 

The Geology of Darling State Park, by Harry W. Dodge, Jr., 1967 .25 

The Geology of Groton State Forest, by Robert A. Christman, 1956 .25 

The Geology of Mt. Mansfield State Forest, by Robert A. Christman, 

1956 .25 

The Geology of the Calvin Coolidge State Forest Park, by Harry W. 

Dodge, 1959 .25 

The Geology of D.A.R. State Park, Mt. Philo State Forest Park, Sand 

Bar State Park, by Harry W. Dodge, Jr., 1969 .25 



*** SPECIAL BULLETIN 

Special Bulletin Mo. I - Geology of the Plattsburgh and Rouses 

Point, New York- Vermon t , Quadrangle by Donald W. Fisher, 
1968 



3.00 



*** OTHER PUBLICATIONS *** 

The Physical Features of Vermont, by Elbridgo Churchi I I Jacobs, 
1950 



I .00 



1830 




Exf^tnnafion of the 
COLOUKfl 

fLATK Caf^oiiift^titL.* A/rrti't/ivns .Vo. £ 
Priniitn-f. .Vo.yjL J'r.itxr. ^^VIIE /.0t*>A 

W V Tertinr^. 

TLLLO^V. (ttl /A^ OH*trfmOJ-f /^/fftttlfturi. 
BCt'X. ttH tn* ett/c*tfOt*S /uriimtftuns 
Mrro. vnriffftit^ff ^,tnt/rfoit» Sii/*/\urf' 
"'^ Suff ^/*ftfie/s «/■ ba-Tfiff- 

OKt:K.\ SCOTS', ha-Ttiffii- rocA^s 

white jAr/f ftitif/^, Afffit/ M^ <■«// 
etMreou^ /or-rnnfion a/~ f/ie S'f* S'-rims 

TAis ColOnr'M wnafi erhtbits n. 
gtna'-ai vietv ©/" the 

ECOSOAttCAI. G F.OLaOY 
• ^AtH'ior-A t\T\U n*irt of the 
adj'otnin^ Stn/^S; ns ifii-rrt^ti 
bjf tf*e honoufo^te Ste/i^^/i I'an 

R»*%as»tamf School 
Te^j Jan. t.t830 




M 



fl 



Fig lo 



om A.Eaton (IS30), OtoioQIc Teitbook.Pt I 

lOOHtilCC 



90 

_1_ 



Scale 



J 



1861 



© 
© 
© 
® 
© 
© 
© 
© 
© 
© 
© 
© 
© 



KEY 

Gneiss 

Tolcose Schist 

Chazy, Bird's Eye, and Black River Limestones 

Trenton Limestone 

Utico Slate 

Hudson River Slates 

Red Sondrock 

Quartz Rock 

Georgia Siotes 

Tolcose Conglomerate 

Eoltjn Limestone 

Beds of Steatite 

Ores of tron older thon ttie Tertiary 







Fig lb 



AtJoptei from the E M .'chcoc ii s flepo' r on ihe 
Geology of Vermont (186'), *ol 2, pi I 



1961 



oversize 

QE 

78.3 

.N4 

1972 




FiQ .c 



Adapttd ffom the Cenlannioi Gco<og>c Mop of 
Vermont by Doll at al (I96i) 



1 



4