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Ami, Henry -fere
EX. BRITISH MEDICAL ASSOCIATION OFFICIAL GUIDE
AND SOUVENIR, PP. 45-49, MONTREAL, 1897.
GEOLOGY OF MONTREAL
By H. M. AMI, M.A., D.Sc.
FELLOW OF THE GEOLOGICAL SOCIETIES OF LONDON,
SWITZERLAND AND AMERICA
PRINTED 15 Y
THE CANADA ENGRAVING & LITHOGRAPHING CO.,
THE GEOLOGY OF MONTREAL.
Fourteen distinct geological formations or hori-
zons have been described within a radius of a
few miles from Montreal. Four of these belong to
the Quaternary or newest system, one is doubtfully
but probably referable to the Devonian, one to
the Silurian (Upper Silurian of Murchison), seven
to the. Ordovician (Lower Silurian and Cambro-
Silurian of many authors), and the remainder to
the Laurentian or part of the great Archaean
A geological map of Montreal and its environs
would comprise four areas marked by four distinct
orographic features worthy of note, as follows :
(1) A more or less hilly and mountainous pla-
teau of Archaean rocks to the north and north-west
(2) A broad, flat, more or less elevated Ordovi-
(3) A number of conspicuous, more or less
elevated conical mountains or hills of volcanic ori-
gin rising through the Ordovician plain.
(4) Alluvium, marine clays and sands, gravel
terraces and raised beaches accompanied by "till"
and numerous phenomena characteristic of the
" Great Ice Age."
2 Jh'itis/i Medical Association
SUMMARY OF THE; VARIOUS GEOLOGICAL FORMATIONS IN
AND AROUND MONTREAL, CANADA, AND SOMF, OF
THKIR MORK SALIENT CHARACTERS.
Exclusive of the fresh-water, lake and river
deposits of more recent times, the Pleistocene forma-
tions, in descending order, consist of the following :
I. SAXICAVA SAND FORMATION, of Eastern
Canada. Characteristic fossils : Saxicava rngosa,
My a arenaria, M. t run cat a, Maconia fragilis.
II. LEDA CLAY FORMATION, marine clays with
occasional sandy partings ; foram in i feral. Fossils :
Leda (Portlandia] arctica, CranieUa Logani, Ophio-
glypha Sarsii, Polystoniella crispa, etc.
III. GLACIAL OR BOULDER CLAYS, TILL. No
fossil remains have as yet been found in the glacial
clays of Montreal.
Localities : St. L,ouis and Mile-End Quarries, the
Tanneries, etc., are excellent collecting grounds for
DEVONIAN ERUPTIVES, ETC. To the Devonian
Epoch are ascribed those nepheline syenite masses,
diabase, and trachyte, and other dyke rocks, which
are so conspicuous and numerous about Montreal,
holding Dawsonite, sodalite, elseolite-syenite, etc.
The eruptive masses comprise Mount Royal, Beloeil,
Montarville, Rougemont, Mount Johnson, etc.
An occasional pebble of fossiliferous Middle
Devonian limestone marks the probable existence, at
one time, of a basin of Devonian rocks in the Mont-
real district, similar to those which are known
to exist farther east along the Famine River, and in
Souvenir of Montreal, 1897 3
the Gaspe Peninsula of Quebec, or to the south
in the Helderberg mountains of New York State.
Such Devonian pebbles occur in the volcanic ag-
glomerates or breccias of St. Helen's Island, just
south of Montreal.
LOWER HELDERBERG FORMATION. Consists of
somewhat limited patches of light gray and compact
more or less altered limestones which abound in
fossil remains, chiefly Brachiopoda. Fossils : Fa-
Tosites Gothlandicus, Leptcena rhoinboidalis, Orthis
cm in ens, StropJieodonta varistriata, S- punctulifera,
Pentamerus galeatus, Spirifer concinnus, S. cyclop-
terns, Atrypa rcticularis, Stenoschisma formosum,
Platyustoma depressum. Locality : South side of
St. Helen's Island.
The Ordovician (Cambro-Silurian and Lower
Silurian) formations in the Montreal district are
seven in number, and from the Lorraine or upper-
most Ordovician in Canada, down to the Potsdam
sandstone there is not a single break in the suc-
cession. From Ste. Anne, a point twenty miles
west of Montreal, to Chambly, there is a complete
section and series of these seven formations in
descending order as follows :
I. LORRAINE ("Hudson River" of many geol-
ogists). Consists of dark brown and black, brittle,
for the most part indurated clay and arenaceous
shales and sandstones. Fossils : Columnar ia alveo-
lata, Catazyga Headi, Pteriuca demissa, Byssonychia
radiata, Orthograptus quadritnucronatus, Clidophorus
pianulatus, Orthodesma parallel-urn, Cyrtolites orua-
ttis. Localities : Chambly, Rougemont, Riviere-
4 British Medical Association
II. UTICA FORMATION. Dark brown and black,
brittle and bituminous shales with occasional bands
of limestone at the base'. Fossils : Reteograptus (?)
eucharis, Leptograptus flaccidus, Lcptobolus insignis,
Scliizocrania filosa* Cornulitcs iuiniaturum, TrocJio-
lites animonius, Triarthrus Bccki. localities : St.
Helen's Island, West End, Point St. Charles, near
III. TRENTON FORMATION. Dark gray fossili-
ferous limestone and shales. Fossils : Glyptocystitcs
Logani, Hcterocrinus tennis, Pachydictya acuta, Plcc-
tainbonitcs sericca, Prasopora Sclwyni, Dalmanc.lla
tcstudinaria, Parastropliia Jiemiplicata, Rajincsqiiina
altcrnata, Treuiatis Montrealensis, T. tci'ininalis,
Glossina riciniforviis, RJiynchotreina iricegu wall/is,
Cyclonema Montrcaleusc, Bellerophon bilobatus, Conu-
laria Trcntonensis, Trochonema umbilicatum, Isotelus
gigas, Calyincna scnaria, Localities : Mile-End and
St. Louis quarries, Lachine, Pointe-aux-Trembles,
IV. BIRD'S EYE AND BLACK RIVER FORMA-
TION. Dark gray impure fossiliferous limestones.
Blocks of this limestone were used in construct-
ing the piers of the Victoria Tubular Bridge.
Fossils : Tetradium fibratuin, Coluinnaria Halli,
Solenopora compact a, Stromatocerium rugoswn, He-
licotoma planulata, Cyrtodonta Hnronensis, Bathy-
urus extans. ' Localities : Pointe- Claire, St. Vin-
V. CHAZY FORMATION. Light and dark gray
fossiliferous limestones. Fossils : Bolboporites Ame-
ricamis, Malocystites Murchisoni, Blastoidocrinus car-
charicedens, Rhynchotrema plena, Lingula Belli,
Orthis, (Hebertelhi) borealis, O. imperator, Bathynnis
Angelini. Localities : Sault - au - Recollet, Back
Mountain, St. Martin, Terrebonne, Caughnawaga.
Excellent building stone.
Souvenir of Montreal, 1897 5
VI. CALCIFEROUS FORMATION. Dark gray, im-
pure, more or less magnesian and arenaceous, fossil-
iferous limestone. Fossils : Pleurotomaria calcifera,
P. Caimdensis, Orthisina grauda'va, Ophileta com-
planata, O. disjuncta, Hormotoma Anna, Metoptoma
simplex, Orthoceras Lamarcki, Ainphion Salteri,
Batliyurus Cybele, Ribeira calcifera, Leperditia Anna.
Localities : Ste. Anne, Caughnawaga, Carillon.
VII. POTSDAM (SANDSTONE) FORMATION.
Light yellow, rusty-weathering sandstones. Fossil
remains : Scolithus Canadensis, Protichnites multino-
tatus, P. lineatus, P. octonotatus, P. septemnotatus.
Localities : Beauharnois, for tracks ; Ste. Anne,
LAURENTIAN. The " Morin area," north of
Montreal, has been recently described by Dr. Adams,
and forms a part of that extensive series of granites
and granitoid gneisses, limestones and anorthosites
so extinsively developed everywhere in North -East-
ern Canada, covering as they do an area of more
than two million square miles.
For a more detailed account of the geology of
Montreal and its environs, the reader is referred
to volume VII of the "Annual Report of the Geo-
logical Survey of Canada," 1896, in which Dr. Ells,
Dr. Adams and the writer present the leading geo-
logical features in the stratigraphy, petrography,
and palaeontology respectively. The " Geology of
Canada," 1863, by Sir Win. Logan, E. Billings,
Sterry Hunt, etc., also contains excellent -details on
the same district, besides other districts of Ontario
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