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OGGASIONAL PAPERS

OF THE

CALIFORNIA
ACADEMY OFSCIENCES

No. XXIIT

A Geological Reconnaissance
of Panama

By ROBERT A. TERRY

SAN FRANCISCO

PUBLISHED BY THE ACADEMY -~- 1956

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A Geological Reconnaissance
of Panama

BY
ROBERT A. TERRY

SAN FRANCISCO
CALIFORNIA ACADEMY OF SCIENCES
1956

OCCASIONAL PAPERS NO. XXIII

OF THE CALIFORNIA ACADEMY OF SCIENCES
Issued March 2, 1956

COMMITTEE ON PUBLICATION

Dr. Ropert C. MILLER, Chairman
Dr. G. F. PAPENFUSS Dr. Epwarp L. KEsseu, Editor

CONTENTS

Page
PEDRO GLIOM MRLs RSet each Re aim TCR A AE eA a SN ST cng 1
Sources and) Aickmowiled ements. ead ete. a afse fos ekg has a Maye facts 1
Sy DLeTE) GOVE EN CoN AUCTIO 275 (MON AU a: Begg AC a ha earn a Ro 3
PCOMPOED MOLI Te tice ad eue rats NING ats eieccube le Siralews Siesne See wate Si 4
NINES Sv ahead 2 62) 008 a eg ee ER geet neal Ae pe eign PSR OA 6
LOPE: T1 Fraga AB SET 217 0 a a a Oe Wr MI ey ea 12
JHE gma] BE ACW ae ne rte ee aires hed kt NAA a Sa at 17
MTG MIS HEC ES rears Shaan ois cs thas, ON omrey ia ce eee ree Bh Ue tea Foe 21
Nie Lamon Gutvoekige. sc). 4 Roc... jedi i eee meet ee oo as 27
re O MM CHIL MR EM EUOCK Gly) cis 1 wh saks: arene Remand a ans Care Side Gee Ahh acl? 28
ORRSUEN CTS” 0U7 NEA, AN Oe OP MIR gs GEE aN Rn IF A a Pte 29
COMO L weret res rs Cy ci Seta eects «te ge RTE TS Meas Soo a tars 29
SOUT COT CM aE iia i tier At cal Nee nl aden sav seis Hic Ae eee Decks Ae 35
IMB GROT er iewe seh Aen cos lelas SaLOaI yo vicar ae aS ee a ate ae Aele 43
WEG CEMVINOCENG. (Sas cee Plame fa, 1.2 haere Suan 49
Upper Miocene:arid Phhocene: <3... 2c ok.s « vite so eee 54
ECISDO CATCH Raye ie. eS. sarant ich w ciol Sess heycvar yee. cis!h Stn ear Sade 60
RCC TAA OE Nee ae Wa cus Eo ovekty rant Pe cee eata) eget dn tile. Ma aes Th eee eens 60
re STULL ED De MSPs co gel deg are EPR gn RENE PR RR Ny oA UR) eet e 60
ASHORE MR Era MA. Sc na el ace cies are poss Bho ais exerts eo hua fetere oie ee 62
Centra Mla Matias ets ile, opie eh eke Losighce. ation ty ote 69
IWeNteRneatiainay ak. och asthe eae e ews crcle deere eeetons 76
cumo mines GEOlQ or rgey ne 5s kainate ese MACs Lele) 0 Mes hits oe epee 83
IB-THOVVayea i GY aye eae Neen oie, SRE ene RED eR el dn Re AY CHE 87
ILLUSTRATIONS
Eiategia » Western Pama al (Seo. 58 3 bers otoe a snats Opposite 12
Piatrewlle Central mamamiar . sci saps oe dss sao os.s Opposite 28
ip leahegaeie. Mastenm wir anaes, 2c eo clas s..ceas) as ota Opposite 44
Plate IV. Land and Submarine Topography—
Caribbean RegiOM -aca5- 26 uo acc ose essa Opposite 60
Figure st. lsthmian Politicals Divisions. 6 /).:00)2.'s2.1e awa sie 5
Figure 2. Topographic Sketch Map—Isthmian Region ........ fi
Figure 3. Geological Reconnaissance Map of a Part of the
1 2271 Mad ASH A a6 RS, MO Eee ye Re a ane AP ae ee 35
Higure 4). Structural Pattern of Panama, ...<)..14.%:s04< 0... 63
BiguUrerS:,, OULUehUbe SCCHOMS, @ «sais tis. ss.0 9 cccles Sate eu Mieke Mone olgs 65
Figure 6. Structure Sections (continued) ................... 67
Figure 7. Fault Pattern—Rio Indio Coalfield ................ 72
Higure. 8. “Areal Geology ot Cana District ..... 04.6. 6.¢62s600 82

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A Geological Reconnaissance

of Panama
INTRODUCTION

SouRCES AND ACKNOWLEDGMENTS

This paper is based primarily on field work conducted by the
author in the Republic of Panama between the years 1920 and 1949.
Much of the exploration was carried on as an independent undertak-
ing, pursued as time and opportunity offered. But of the period
involved, seven years were spent in the service of the Sinclair Panama
Oil Corporation, to whose parent companies, the Sinclair Oil Com-
pany and the Cities Service Company, the writer is indebted for the
privilege of publishing material from the files, including not only his
own work, but that of a previous party which covered a considerable
part of the area in 1917 and 1918, as well as material derived from
well logs, and results of paleontological examinations of collections
from wells and from the field. In this connection, gratitude is espe-
cially due to Mr. F. A. Bush, Dr. W. B. Heroy, and the late Mr. A. C.
Veatch.

The Gulf Oil Company has given generously of its store of infor-
mation acquired over years of exploration and drilling in the Gara-
chiné area of Darien Province. The Panama Corporation of Canada,
Ltd., through Messrs. Beresford, Benagh, and Retallac, furnished
maps and information; and other members of its staff gave advice
and assistance in the study of Panama’s most famous mine, the Espi-
ritu Santo, of Cana in Darien Province. The officials and staff of the
United Fruit Company and its subsidiary, Chiriqui Land Company,
have rendered innumerable services of many kinds. Gratitude is espe-
cially due to Mr. H. S. Blair, former manager; Mr. Rudolph Jensen,
one-time chief engineer; and Mr. F. W. Genuit, once special agent;
all of the Chiriqui Land Company at Puerto Armuelles.

Many officials of the Republic of Panama have offered encourage-
ment and assistance, including two presidents of the Republic, Dr.
Harmodio Arias Madrid, president from 1932 to 1936, whose letter to
local officials greatly facilitated the work during this period; and the
late Don Domingo Dias Arosemena, president in 1948 and 1949, to
whom the writer is indebted for the opportunity to study in detail the
aerial photographs of the Republic.

From various members of the staff of the Panama Canal, particu-

[1]

MAR

2 i956

2 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

larly the late Mr. R. Z. Kirkpatrick, for many years Chief of Surveys
of the Bureau of Maintenance and Operations, there has been received
much valuable information and assistance. Dr. D. F. MacDonald, late
Geologist of the Panama Canal, and his successor, Mr. T. F. Thompson,
placed much information at the writer’s disposal, and offered oppor-
tunities to visit areas otherwise inaccessible.

Dr. T. W. Vaughan, of the United States Geological Survey, fur-
nished the results of a preliminary examination of fossils submitted
to him jointly by Mr. A. A. Olsson and the writer. Dr. G. D. Harris
of Cornell University and Dr. H. N. Coryell of Columbia University
generously undertook the identification of fossil collections; and other
paleontologists, notably Dr. Katherine Van Winkle Palmer, G. D.
Tash, and A. D. Brixey, Jr., furnished fossil identifications and
offered useful suggestions. Dr. L. G. Hertlein of the California Acad-
emy of Sciences and Mr. C. C. Church, research associate of the same
institution, and Dr. Hans Thalman of Stanford University checked the
nomenclature of the foraminifera identified from well cuttings, and
also the mollusks collected in the field. Dr. E. R. Dunn of Haverford
College generously took time to collect rock specimens and make geo-
logic observations in the highest part of the Azuero Peninsula, a region
from which no other information was available.

However, more than to any other individual, the writer is indebted
to A. A. Olsson for advice, encouragement, and active assistance in
field and office.

The Lake Nicaragua, Panama, Bogota, and Barranquilla sheets of
the 1:1,000,000 map published by the American Geographical Society
of New York, the Lake Nicaragua, Panama Canal, Peninsula of Azu-
ero, and Cape Corrientes sheets of the World Aeronautical Chart,
published by the Aeronautical Chart Service of the United States Air
Force, have furnished the topographic basis for the maps of the land
areas, Supplemented by various maps of surveys by the Department of
Maintenance and Operation of the Panama Canal, and by maps of the
various oil, mining, and fruit companies listed above. In some areas,
where no such surveys have been made, the writer has made his own.*

The positions of the isobaths have been taken from the 1:5,000,000
“Map of the Americas” of the American Geographical Society of New
York, and from many of the charts issued by the Hydrographic Office

*Discrepancies between elevations as given in the text and as shown on the map are due
to recent information arriving too late for inclusion in the map. The elevations cited in the text
are taken from the World Aeronautical Charts published by the Aeronautical Chart Service,
U. S. Air Force, Washington, D. C., as follows:

769. Panama Canal, Canal Zone-Colombia-Panama. 8th edit. revised, December, 1953.
829. Cape Corrientes, Colombia-Panama. 7th edit., April, 1954.
830. Peninsula of Azuero, Costa Rica. 5th edit., August, 1953.

No. 23] TERRY: GEOLOGY OF PANAMA 3

of the United States Navy, of which charts numbers 2015a, 5011a,
5018a, and 1176 have been particularly useful for areas outside the
continental shelf. In addition, the writer secured from the Hydro-
eraphie Office, photostats of the “smooth sheets” for most of the
Pacific coast and for the Caribbean coast of the Province of Bocas
del Toro, and adjacent shores of Costa Rica. Since the ‘‘smooth sheets”
contain all the soundings instead of the three to five per cent usually
shown on the Hydrographic Charts as issued, an enormous amount
of detail is made evident which would be unsuspected from a study
of the Hydrographic Office charts. Canal Zone geology as shown is
adapted from the published maps of MacDonald (1915) and Jones
(1950) with some slight modifications.

In 1934, the writer, at the request of Professor Charles Schuchert,
submitted to him for publication in his “Historical Geology of the
Antillean-Caribbean Region,” a geologic map of Panama which had
been compiled by the Geology Department of the Sinclair Oil Com-
pany some fifteen years earlier. A much-reduced and altered version
of the map was included in Schuchert’s volume. Since that time two
maps, sponsored by the Geological Society of America and the United
States Geological Survey, have been published. All these maps are
on a seale too small to furnish more than a generalized idea of Isth-
mian geology. It is hoped that the map presented herewith may be of
use to persons interested in the subject, who desire greater detail.

Geologists who have worked in the rainy tropies know the diffi-
culties imposed by heavy vegetation, deep weathering of the rocks,
and unfavorable climate. These difficulties are encountered in the
most extreme form in Panama. In addition, difficulties in correlation
due to lithologie uniformity, and overlapping of fossil species that in
other regions are distinctive, make it difficult and in many cases
impossible to draw contact lines. Even in the Canal Zone, which
has received many times as much attention as any other part of
Panama, there are still doubtful contacts and correlations. The
writer can only hope that the inevitable errors on the map will not
prove too embarrassing.

GENERAL FEATURES

The Republic of Panama lies between parallels 7° 9’ and 9° 37’
N., and meridians 77° 9’ and 85° 1’ W., with a maximum east-west
extension of about 390 miles and a maximum north-south extension
of about 170 miles. Its area is about 29,000 square miles. Of this
area probably less than half is permanently inhabited. Approximately
one-half the country is above the 1,000-foot contour, but perhaps
ninety per cent of the population live below it. All the provincial

4 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

capitals and also the national capital are below the 100-meter (328-
foot) contour. In spite of the fact that Panama has been a highway
of international ecommerce for more than four hundred years, con-
siderable areas are still known only vaguely. The continental divide
is erossed by only two highways and one railway, all of them within
or adjacent to the Canal Zone, and it is crossed by few trails. Even
in the lowlands, large tracts of most fertile soils remain uncultivated.

The topography has been accurately mapped only in the vicinity
of the canal, such portions of the coast or other areas as the United
States War Department has considered of strategic importance, and
in the immediate vicinity of the Pan-American or Inter-American
Highway. Other mapping has been done by oil, mining, and fruit
companies, and it is of a limited and sketchy character. The country
has been photographed from the air for the purpose of constructing
an accurate topographic map, but this project will not come to fruition
for some years. .

About 1,700 square miles in the Intendencia of San Blas, and
adjacent areas of the provinces of Darien and Panama are under the
control of the Cuna Indians, and are not open to exploration except
with their consent, which is almost never given. The topography of
this region is known mainly from air observation, although two eross-
ings of the Intendencia of San Blas have been made under military
protection, one in 1870 by Selfridge and another in 1947 by Thompson.

GEOMORPHOLOGY

The general form of the country is an irregular sigmoid, elongated
in an east-west direction. Its outlines are broken by one large and
several small peninsulas; the large one—the Azuero Peninsula—form-
ing the west shore of the Gulf of Panama. This, with two smaller
ones, the Burica Peninsula and the Sond Peninsula, are on the Pacific
coast; two still smaller ones, the Valiente and San Blas peninsulas,
are on the Caribbean coast. If the ocean were withdrawn to the 100-
fathom isobath, the area of Panama would be increased by about
one-third, most of the addition being on the Pacific side. The elongated
sigmoidal form would still be preserved, but the large Azuero Penin-
sula would no longer be recognizable.

The eastern end of the country is in a more advanced stage of the
erosion cycle than the western, and this difference extends across the
national boundaries, with the flat basin of the Tuira River of Darien
Province merging with the swampy plains of the Atrato in Colombia;
while in the west, the rugged continental divide between Bocas del
Toro and Chiriqui rises to the lofty voleaniec peaks of Costa Rica

No. 23]

TERRY: GEOLOGY OF PANAMA

Isthmian

Political

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Isthmian political divisions.

Figure 1.

6 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

(fig. 2). The coastal plain and adjacent lowlands are wider on the
Pacific than on the Caribbean side, and this difference extends out
to the edge of the continental shelf. If the map were continued to
the northwest, the relations between the coastal plain and the conti-
nental shelf on the two coasts would be seen to reverse itself, the
plain on the Caribbean side becoming wider, that on the Pacific nar-
rower. This physiographic change is evidently the surface expression
of a change in the underlying rock structure.

WESTERN PANAMA

The lowlands of the Pacific side of western Panama can be divided
into five distinct physiographic provinces:

1. The Burica Peninsula, on the international boundary at the
southwestern corner of Panama and the southeastern corner of Costa
Rica, is a tightly folded and faulted area, the exposures showing rocks
of the basement complex and the entire known sedimentary section
of Panama, with the possible exception of the Oligocene, which has
not been identified, as yet. Marine Pleistocene occurs at elevations
of 100 feet or more. The maximum relief is over 2,500 feet, with the
highest point within a mile of the west shore, and the divide between
the east-flowing and west-flowing drainages lies close to the west coast
from this point to the tip of the peninsula. The short high-gradient
streams flowing west are rapidly beheading the long low-gradient
streams flowing east. The rocks of the basement complex are mostly
in the northwest corner, and the sedimentaries curve round them in
arcuate forms, convex to the northeast. Differential resistance to ero-
sion has resulted in a rugged topography, but the surface of the high
ridge of basement rocks is so smooth as to suggest peneplanation prior
to the last elevation. An extension of this surface tilted to the north-
east at about 3 degrees would meet the successive crests of the ridges
of sediments, indicating that the entire peninsula was once peneplaned
and then tilted to the northeast in late Pliocene or Pleistocene time.
In Recent time the peninsula was an island, and it is now a tombolo
tied to the mainland by delta deposits. There is almost no continental
shelf on the east side, but there is one on the west side, two to three
miles wide.

2. The flat lands at the head of the Burica Peninsula, composed
of Recent alluvium, occupied by the banana farms of the Chiriqui
Land Company are a composite delta formed by rivers from the main-
land and from the peninsula. Until recently a residual lake remained
near the center of the area. This flatland extends from Golfo Dulce
on the west to Rio Chiriqui Viejo on the east. Water wells of the

GEOLOGY OF PANAMA

TERRY

No. 23]

‘UOIZal URIWIYS]—deuU Yo Jeys o1ydeisodoy, “Z siNsly

8 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

Chiriqui Land Company have penetrated more than 200 feet of allu-
vium. An ancient river system, now submerged, crosses the continental
shelf. (Terry, 1941.)

3. A volcanic outwash plain extends from the Rio Chiriqui Viejo
on the west to the vicinity of David on the east. The maximum relief
is 900 feet. Voleanie ejecta cover folded Tertiary sediments. The
region is a smooth plain for the most part, but hills of Tertiary sedi-
ments appear near its northern edge. Near Concepcion about 14 miles
from the coast, a fault-line escarpment separates it from the higher
area to the north, in which the streams run in deep box canyons, while
below the searp the channels are shallow, and the streams run out of
control in the rainy season. The coastal margin is swampy. The con-
tinental shelf widens from 10 miles at the west to 20 miles at the east.

4. David to Tolé. This is a maturely dissected belt of tilted and
folded Tertiary sediments, with numerous plugs, dikes, sills, and flows
of andesite. The igneous outcrops and the numerous faults interfere
with the normal development of the erosion pattern. Most of the
streams are consequents. The maximum relief is about 1,000 feet, but
the average is less than half that. The high points are mostly voleanic
plugs, dikes, or lava-capped mesas like the Gran Galera de Chorcha.
The coast line is serrated with numerous small islands, and the lower
stream courses have been drowned by recent invasion of the sea. The
continental shelf widens from 20 miles at the west to 50 miles at
the east.

5. Peninsula of Sond. This is a rugged igneous area, the rocks
being mostly or entirely basement complex. The maximum relief is
about 1,500 feet. There is a ria coast and the continental shelf is
about 50 miles wide.

On the opposite, or Caribbean coast, some four coastal provinces
may be distinguished:

1. Puerto Limon to Old Harbor (Costa Rica). This is a flat
swampy coastal plain, two to five miles in width, with an extension
up the valley of the Estrella River ending in a bolson valley floored
with gravel and boulders, with a thin cover of alluvium. Smaller
valley flats extend up the Banana and Bananito rivers. The alluvial
cover of the coastal plain is thin over folded Tertiary sediments, which
are occasionally exposed in stream beds. Drowning of stream valleys
is less marked than on the opposite coast of Chiriqui. The continental
shelf is seven to eight miles wide from Puerto Limon to Cahuita
Point, whence it narrows rapidly to about two miles at Old Harbor.
The straight line of the coast suggests fault control, and the rapid

No. 23] TERRY: GEOLOGY OF PANAMA 9

narrowing of the continental shelf east of Cahuita Point, with its steep
outer edge carries a similar suggestion.

2. Old Harbor to Monkey Point (Costa Rica). This region has
no coastal plain. It is composed of sandstone and conglomerate hills
of middle and late Miocene age with some Pliocene. These form a
belt of hills along the coast, back of which is the flat meander belt of
the Sixaola River, about five miles wide. The continental shelf is
about two miles wide.

3. Monkey Point to Chiriqui Lagoon (Panama). This area con-
sists of a swampy coastal plain, seven to eight miles wide, over which
the Sixaola and Changuinola rivers meander. The wide flood plain
of the Sixaola extends inland to the bolson Talamanca valley, filled
with heavy gravels and boulders with a thin cover of alluvium. The
continental shelf is seven to eight miles wide and at the mouth of the
Sixaola is deeply notched, apparently because of faulting. (Terry,
1941.)

4. Almirante to the base of the Valiente Peninsula. This region
consists mainly of the shallow, flat-bottomed Chiriqui Lagoon, which
has a maximum depth of about 20 fathoms. In the lagoon are nu-
merous islands of Miocene sandstones and shales, with interbedded
and intruded lavas. Along the inner margin of the lagoon from Almi-
rante to Chiriqui Grande, similar hills of sediments and andesite
form the coast, but from Chiriqui Grande to the base of the Valiente
Peninsula is a swampy, alluvial coastal plain, five to six miles wide.
The Valiente Peninsula is a tombolo of Miocene sediments and igneous
rocks. The continental shelf varies from about 5 miles wide at Vali-
ente Point to 20 miles at the offshore island, Escudo de Veraguas,
from which it narrows rapidly to 10 miles at the base of the penin-
sula.

Between the two coastal regions just described, the cordillera of
the continental divide rises from about 3,000 feet at the head of the
Rio Tabasara at the eastern edge of the region to 12,861 feet at Chir-
rip6 Grande, southwest of Puerto Limon. The axial portion of the
eordillera may be conveniently divided into three parts.

1. Eastern part, the Serrania de Tabasara. The crest of the cor-
dillera rises from 3,000 feet at the head of the Tabasara, to 9,265
feet at Cerro Santiago, a Pleistocene (?) voleano, from which it de-
scends to about 4,000 feet near the 82nd meridian. There is a fairly
even slope on each side to the two coastal plains, with consequent
streams running straight down the slope.

2. Central part from 82° to 82° 30’ W. The crest line has an
average height of 5,000 to 6,000 feet with three peaks—Hornito

10 CALIFORNIA ACADEMY OF SCIHNCES [Oc. PAPERS

(7,200), Cumbre de la Playa (8,235), and Horqueta (7,440 feet).
These are apparently all voleanic, probably of late Pliocene or Pleis-
tocene age, but they have not been investigated. The writer crossed the
divide on a trail between Hornito and Cumbre de la Playa, and noted
the flatness of the divide for a width of a mile, more or less; and he
was informed that the Rio Chiriqui rises in a shallow lagoon in a
similarly flat area on the crest of the divide. It is not known whether
the flattening is erosional or due to flat-lying lava beds, but the last
rocks exposed on the south side before reaching the crest, are crystal-
line, followed by andesite at the crest, but no flow structure was seen.

3. Western part—the Cordillera de Talamanca. This portion of
the cordillera has eight peaks above 10,000 feet on the divide itself,
and four others at short distances from the crest-line. The writer has
not crossed this part of the divide, but has climbed one of the peaks
on the south side, El Bari, a Pleistocene voleano. Reports of its ac-
tivity in historic time are of questionable authenticity.

El Bari, which dominates the landscape from almost any point
in the province of Chiriqui, is for that reason usually known as the
Volean de Chiriqui. Its peak, 11,410 feet above sea-level, is the highest
point in the Republic of Panama, and is about eight miles south of
the continental divide. The present cone, which is far from perfect,
has an ellipsoidal base about nine miles long on the main axis, which
extends on a nearly east-west line, and about seven miles on the
shorter axis. This cone is composed mainly of heavy flows of andesite
and subordinate amounts of clastic material. Examination of slides
made from these Pleistocene flows does not disclose any perceptible
difference from slides cut from flows of Miocene age or those of the
basement complex.

There are several craters, the largest of which lies west of the high
peak and debouches through an opening half a mile or more wide
upon the Llanos del Volean, a gently sloping plain, from which rise
a few small andesite hills, which may be voleaniec plugs, or remnants
of older flows. There are several undrained depressions, two of which
are occupied by perennial ponds. The material underlying the sur-
face, so far as can be seen in the erosion channels, is mainly clastic
and most of it appears to have been water deposited.

From the Llanos del Volean a continuous gentle slope extends
southward some eighteen miles to Concepcion, where it is intersected
by an eroded fault searp. This sloping plain is drained by radial
streams, running in deep box canyons. The interfluvial areas are
wide and not much dissected on the upper part of the slope; the lower
areas are more cut up, but the entire region has an appearance of

No. 23] TERRY: GEOLOGY OF PANAMA 11

extreme topographic youth. The material is mostly clastic and was
distributed by explosion and by water. The breach in the old crater
wall suggests that a crater lake was released by faulting or by erup-
tion, the succeeding floods spreading loose materials which were car-
ried farther by slope wash. It is possible that other vents contributed,
but by far the greater part was apparently derived from El Bari.
The area covered by the voleanics has maximum dimensions of about
25 miles east-west and about 30 miles north-south. Near the peak on
the east are three small craters of later date with steep andesite walls
and flat floors, largely pumice. Narrow notches in their walls cut by
the overflow lead to the Cochea River. There are no signs of recent
activity in the small craters, but there is a tepid sulphur spring in
the large one.

The base of the lava flow cone is overlapped by the elastics, and the
platform on which it rests is not visible, but is presumed to consist
of sediments of Mid-Miocene age which emerge from beneath the
elastics at both the east and west margins of the voleanic area at
altitudes of 3,000 to 4,000 feet.

The writer has crossed the continental divide a few miles west of
Cerro Santiago at the head of the east fork of Cricamola River, and on
the south side of the divide crossed a steep slope of voleanice ash which
looked as fresh as the material in the crater of Irazi, an active Costa
Rican voleano. The ash was so loose that the accompanying Indians
insisted on spreading out to a spacing of 30 feet between men, to avoid
starting a slide. It was the writer’s impression that Cerro Santiago has
been more recently active than El Bart. Most of the high peaks in
this part of the Cordillera are probably voleanie and of Pliocene or
Pleistocene age, but the divide has not been examined except here and
at the crossing between Rio Chiriqui and Rio Guarumo.

The Cordillera de Talamanca continues northwestward in Costa
Rica, trending slightly more to the west, and increasing in altitude,
to Chirripé Grande at 12,861 feet, from which it descends slowly to
the Meseta Central of Costa Rica. According to Lohman (1934), the
latter portion is composed of Tertiary sediments dipping north under
the cover of Pleistocene and Recent voleanies in the Meseta Central.
He shows these sediments as resting on a basement of crystalline
deep-seated rocks, which are here and there covered by Pliocene,
Pleistocene, or later voleanics; and he considers the erystallines to
be older than the basic lavas which cover them. Gabb (1875) con-
siders the granite of Pico Blanco, near the continental divide just
west of the international boundary to be a later intrusion which has
metamorphosed the Mid-Miocene sediments. The writer thinks Gabb

12 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

was mistaken, as the Gatun conglomerate contains pebbles and cobbles
of granite. In general, the topography of the cordillera is distinctly
youthful; but there is an area on the Pacific side of the divide near the
international boundary which shows considerable stretches of smooth
surface beveling the steeply tilted Oligocene and Miocene strata. These
sloping plains at the 3,000- to 4,000-foot level are very clearly seen
from the air in the region from Brefion to Canas Gordas. They slope
gently to the southwest and the beveling of the surface is believed to
be of contemporaneous origin with that of the now-dissected peneplane
beveling the ridges of the Burica Peninsula. Both peneplanes dip
inward toward the intervening flats of the compound delta which ties
Burica Peninsula to the mainland. This delta is still close to sea level.
The inward tilting of the peneplaned areas is believed to be due to
underthrusting from the Pacific side, and to intrusion from below
under the cordillera.

CENTRAL PANAMA

On the south shore of the Azuero Peninsula, an andesite cliff
fronts the sea for most of the distance from Punta Naranjos to Punta
Biearu. The narrow width and steep outer edge of the continental
shelf suggest close offshore faulting. Near Rio Ocones, west of Morro
Puerco, shales and slates apparently underlying the andesite, dip
steeply toward the sea. No fossils were found. It is possible that
these rocks are of Cretaceous age, but in any ease the andesite belongs
to the basement.

From Morro Puerco, a narrow coastal plain widens gradually to
Punta Bicaru, where it meets the floodplain of Rio Tonosi. This flat
extends inland for six or seven miles. From Punta Bicaru eastward to
Cape Mala the continental shelf averages about 10 miles in width, but
the coastal plain narrows eastward from the mouth of Rio Tonosi to the
limestone-andesite contact, about eight miles distance, where the ande-
site cliffs reappear and form the coast line to Capa Mala, and north
along the shore of the Gulf of Panama nearly to Mensabé, where a nar-
row coastal plain begins and widens slightly northward to the deep re-
entrant occupied by the delta of Rio Santa Maria. Here the coastal
plain merges with the Santiago plain which separates the highlands
of the Azuero Peninsula from the foothills of the continental divide.
This is a flat erosional surface cut on Oligocene and Miocene sedi-
ments, for some forty miles westward to the head of Montijo Bay.
These flats extend south along the coast of the bay about 25 miles to
the igneous-sedimentary contact north of Rio Toro. The Oligocene
and Miocene are intruded and interbedded with basic lavas and tuffs

No. 23] TERRY: GEOLOGY OF PANAMA 13

over the entire area, a condition which continues north to within a
few miles of the continental divide and east to the vicinity of Anton.
Numerous vents through which these voleanics issued can be seen in the
form of dikes and voleaniec craters, one of which is described by Jou-
kowsky and Clere (1906): “From the port of Aguadulce to Chitré
passing through Sta. Maria, Parri, Parita, and l’Harena describing
an are more or less parallel to the shore with a total length of more
than a hundred kilometers I saw nothing but eruptive rocks, lava, or
ash. South of Sta. Maria is found a cireular plain completely sur-
rounded by a chain of low hills. At its highest point is an outcrop
of basic rock with augite microlites. The general arrangement of the
rocks suggests a voleaniec vent. There are also voleanic rocks, lavas,
and cinders which are found from the village of Chitré to the port,
forming a plain a little above sea level. On the road from Chitré to
Macaraeas for a dozen kilometers, one sees nothing but voleanics. At
this distance (roughly ealeulated) is the first sedimentary outcrop, a
caleareous marl striking NNE.” (Author’s translation.)

Other similar and larger voleanie vents ean be seen west and north-
west of Aguadulee.

The lavas along the coast near Chitré mentioned by Joukowsky
apparently overlie the sedimentaries of late Oligocene and early
Miocene age, and may be younger than early Miocene. The sediments
dip beneath them near Las Tablas and at other points. The peneplane
which cuts across them ean hardly be older than middle Miocene since
it bevels early Miocene strata. The coastal plain continues east beyond
Anton to Chame, and from the coast the smooth gentle slope continues
50 miles beneath the sea to the edge of the continental shelf.

The Azuero Peninsula, aside from the coastal plain, consists of
two upland areas, separated in the middle by the Tonosi basin and
its narrow connection with the Santiago plain by way of Juanbacho
and Macaraeas. The highland area west of the Tonosi basin is a deeply
dissected plateau, which like the Burica Peninsula, fronts the Pacific
with a steep andesite cliff, the highest point of which is less than three
miles from the coast, with the drainage running northwest to the Gulf
of Montijo. The east side of the plateau is separated from the Tonosi
basin by a steep scarp, striking about N. 23° W. The western half of
the Azuero Peninsula has thus the appearance of a fault block, ele-
vated on its eastern and southern sides and tilted to the northwest.
The plateau area east of the Tonosi basin is somewhat smaller and
rises to lesser heights, with no obvious suggestion of tilting. The rocks
of higher parts belong mostly to the basement complex, but some of
the voleanics are younger. MacDonald (1937) considered Cerro

14 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

Quema to be a Pleistocene voleano. The drainage is radial from the
central area of the eastern plateau.

On the opposite Caribbean coast, the continental shelf varies from
3 to 12 miles in width, and there is no coastal plain from Rio Pasaula
eastward to Belen. Over this distance, the andesite foothills of the
cordillera come down to the sea, and are cut up by sharp V-shaped
valleys striking N. 45° W. at an acute angle to the coast, instead of
running directly down the slope from the continental divide, as might
be expected of consequent streams running over unstratified rocks.
The parallel stream courses and unexpected orientation suggest con-
trol by faulting.

From Belen east to Coclé del Norte the surface as seen from the
air, is a series of low parallel ridges striking east-west and rising
slowly to the continental divide, which for a distance of twenty miles
east of La Pintada averages about 2,000 feet in height. The ridged
surface resembles the Santiago plain, and like it seems to be composed
of interbedded clastics and voleanies, the latter forming all, or nearly
all, the formation on the west, with the clastics increasing to the east.
Near Coclé del Norte, specimens seen by the writer were dark gray to
black foraminiferal shale resembling the Useari of early Miocene or
late Oligocene age, which had been intruded by an andesite dike and
slightly mineralized along the contact. However, on a canoe trip up
the river, all exposures seen were igneous. The ridged surface of the
flows and clastics, looks like a peneplane which has been slightly ele-
vated, tilted toward the north, and somewhat eroded. This conclusion
is supported by the fact that east of Belen the stream courses are in
general normal to the coast, as might be expected on a tilted pene-
plane sloping to the sea. It is the writer’s conclusion that this surface
is actually of equal age with the south coast peneplane, but has suf-
fered greater elevation and tilting in post-Miocene time. The corru-
gated surface is the result of erosion of the weaker beds, following the
tilting.

This corrugated surface becomes flatter and wider as one ap-
proaches the canal, bending south to include Gatun Lake, but east of
the lake is cut off sharply by the contact with the basement rocks.
This contact strikes about N. 30° E., reaching the sea about halfway
between Colon and Portobello. On the Pacific coast, igneous plugs
and dikes rise above a surface which appears to be mainly andesite
flows west of Anton, and rhyolite flows and tuffs to the east, with
some interbedded clasties, partly marine and partly terrestrial. Like
the area described above, the surface in general appears to be an ele-
vated, tilted, and slightly eroded peneplane east of the Bay of Chame.

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No. -23] TERRY: GEOLOGY OF PANAMA 15

Between these two tilted peneplanes is a mountain group, flanked by
two voleanie cones, El Valle on the south, San Miguel de la Borda
on the north, between which the continental divide traverses an area
of rhyolites and granites which culminates at the east in La Campana,
3,300 feet in height. The voleanics of El Valle are rhyolite ash
and rhyolite flows. Those of San Miguel de la Borda have not been
investigated.

The well-preserved slopes of the El Valle cone with their youthful
drainage channels, led the writer to ascribe to it [in Schuchert’s
(1935) volume] a Pleistocene age. Jones (1950) objects to this and
apparently considers it Miocene, saying that the slopes have not been
eroded because of the porosity of the tuffs. It is difficult to reconcile
this view with the fact that several voleanoes of Miocene age in the
area between Santiago, Aguadulce, and Las Tablas have been com-
pletely eroded and the surface peneplaned as described by Joukowsky
and Clere (1906). Some of these Miocene voleanoes were of a size
comparable to El Valle. It is a fact, however, that the materials
ejected by the El Valle voleano are considerably older than the cone
itself, and may be of Miocene age. The El Valle volcano is of the
caldera type. Its crater was localized by the intersection of four
faults, two striking N. 10° W. and two striking N. 60° E. The two
latter parallel the continental divide, which is probably itself a fault
line scarp. The north and west walls of the El Valle crater are rhyo-
lite, the south wall and at least a part of the east wall rhyolite tufts
and ash, very well stratified. They strongly resemble the Panama
tuffs at Diablo Heights in the Canal Zone, and may well be of the
same age (early Miocene). The eruptions which formed the cone,
however, took place at a much later date, and the Miocene ash was
ejected after the manner of the Krakatoa eruption, with a minimum
amount of new material. On the floor of the crater, about three miles
northwest of the village of El Valle, a well was drilled to secure a
domestie water supply for the home of Don Enrique Coronado. This
well penetrated 65 feet of tough blue clay, capped by three feet of
loose sand, neither of these deposits resembling the stratified ash of
the crater walls. The well was unsuccessful. The clay is apparently
a lake deposit, made in a water body which filled the crater. The
lake was finally drained by the head of Rio Anton cutting along the
shattered rhyolite on one of the N. 60° E. faults along which move-
ment has taken place in Recent time.

On the north side of the divide, the San Miguel de la Borda cone

has not been investigated by the writer, but as seen from the air,
appears to be a voleanic ash cone, somewhat smaller than El Valle.

16 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

Central Panama, east of the canal, has a well-developed coastal
plain on the Pacific side, which widens from two miles at the eastern
limit of Panama City to 15 miles at the Bayano River. The flat sur-
face continues beneath the sea to the edge of the continental shelf,
about 75 miles distant at the widest part. On the surface of this
plain appear a few monadnocks of igneous and sedimentary rock,
those offshore forming the Pearl Islands and other smaller islands of
the Gulf of Panama, while the inland monadnocks of the coastal plain
are on a smaller seale, but of the same general character. This plain,
like the Santiago plain and that of eastern Chiriqui is cut across
the edges of tilted marine sediments of Oligocene and Miocene age,
which are interbedded with, and intruded by basic voleanics, less
numerous than those of Chiriqui. The continental shelf is ended at
the south by an arcuate escarpment, convex to the north, with a
maximum height of 10,000 feet, and a maximum slope of about 20°.
It is almost certainly due to faulting. A conspicuous narrow slot
bisects the continental shelf in a north-south direction just west of
the Pearl Islands, and during the Pleistocene withdrawal of the sea,
was occupied by the channel of the Bayano River. No such subma-
rine channel connects the mouth of the Tuira River of Darien with
the edge of the continental shelf, although the Tuira discharges a
much greater volume of water than the Bayano. It is therefore be-
heved that the slot west of the Pearl Islands is not due to Pleistocene
stream erosion but to faulting. A similar rift about 20 miles long
euts the smooth surface of the continental shelf southeast of the
Pearl Islands (plate III). It has a maximum depth of 300 to 350
feet, and a maximum width of two miles. It parallels the coast and
is also evidently due to faulting. It is closed at both ends.

An interesting feature of the continental shelf on the two sides
of the isthmus is that on the Caribbean side, the shoulder which
marks the top of the outer escarpment is around the 42-fathom
isobath, while on the Pacific side it is around the 72-fathom isobath,
except along the eastern side of the Burica Peninsula and the west-
ern half of the Azuero Peninsula. Since this shoulder is no doubt
related genetically to the Pleistocene withdrawal of the sea, it would
appear that the present difference in elevation indicates differential
movement in post-Pleistocene time on a regional seale, with sinking
on the Pacific side.

The continental shelf on the north coast of central Panama, east
of the Canal Zone, averages about 10 miles in width and its outer
edge parallels the coast in a gentle arc, convex to the north. There
is no continuous coastal plain, but rather a series of small terraces

No. 23] TERRY: GEOLOGY OF PANAMA 17

notched across the igneous rocks of the basement. They are seldom
more than a mile or two in width, and are interrupted by fingers of
the interior plateau extending to the sea.

The interior plateau is dominated by an arcuate ridge, convex
to the north which marks the northern edge of the basin of the
Chagres. The crest of the ridge varies from 1,500 to 2,000 feet in
height with occasional peaks, the highest of which, Cerro Bruja,
reaches 3,200 feet. The ridge is breached by a fault rift which is
occupied to the south by the Boqueron River running to the Chagres.
This rift is occupied by sedimentary rocks of unknown age, but the
ridge itself is, so far as known, entirely igneous, and belongs to the
basement complex. The rift mentioned above strikes about N. 20° E. A
much larger rift, or graben, forms the basin of Chagres River; the low-
est part of the downthrow block is now occupied by Madden Lake. The
basin of the Chagres lies between two major faults striking N. 70 E.,
and is cut by another system striking N. 20° E. to N. 80° E. These two
fault systems control the drainage pattern of the Chagres and extend
to the Caribbean coast, where the eastern end of the Chagres rift is
oceupied by the Gulf of San Blas. The part intervening between the
Gulf of San Blas and the Madden Basin has been little explored,
but is supposed to consist entirely of the igneous rocks of the base-
ment complex. The topography is exceedingly rough, eut by V-shaped
stream valleys, and may be classified topographically as a mountain
region in early maturity. Looked at from the air, it appears to be
topped by the remnants of a peneplane at about 2,500 feet, with a
few rounded monadnocks rising to 3,000 feet. The size of the remain-
ing flat remnants of the peneplane is not known, but they cannot
be large.

The writer crossed the divide on a traverse from Chepo to the
head of the Gulf of San Blas (plate IIIT) and observed the flatness
of the crest between the head of the south-flowing Mamoni and that
of the north-flowing Samgondi, tributary of the Mandinga. The flat
area was narrow, and apparently not due to flat-lying lavas.

EASTERN PANAMA

In eastern Panama, the ridge of basement rocks forming the south
escarpment of the Chagres-San Blas graben continues, constituting
the continental divide, which extends from the head of the Gulf of |
San Blas to the Colombian border at Cerro Gandi, and continues to
and beyond Cerro Tacarcuna. It lies 5 to 10 miles from the Caribbean
coast, and is an arcuate igneous ridge convex to the northeast, for
the most part less than 2,000 feet high, with some notches less than

18 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

1,000. It is bordered on the south and southwest by a parallel arcuate
lowland, a continuation of the Pacific coastal plain of central Panama.
Most of this plain is below the 300-foot contour. The northwestern
end of this arcuate lowland is oceupied by the basin of the Bayano
River, the southeastern end by the Tuira-Chucunaque basin. The two
basins are separated by a divide so low as to be almost imperceptible
from the air. Indians of the upper Chucunaque have told the writer
that piraguas (Indian dugouts) are sometimes dragged across the
divide from one drainage system to the other. In both basins the
level surface of the lowland is cut across tilted sediments of Oligocene
and Miocene age. The youngest of these, the Chucunaque formation,
is of late Miocene and perhaps Pliocene age. The erosional beveling
must have been accomplished mostly in Pleistocene time. At the
Bayano-Chucunaque divide the lowland is 10 to 12 miles wide, but
from the divide it widens rapidly to the south, and in central Darien
Province reaches a width of 30 miles, which with the exception of a
few monadnock ridges has been not only peneplaned, but largely
base-leveled, so that hundreds of square miles are practically at the
level of high tide. This base-leveled swampy region extends from the
Chucunaque at the mouth of the Sucubti to Real on the Tuira, and is
bounded on the west by the Rio Sabana and Lower Rio Tuira from
the mouth of the Lara to Chepigana on the Tuira and thence south
to Tuecuti on the Rio Balsa, enclosing an area of about 600 square
miles. This area is uninhabited except at its outer edges, and was
apparently uninhabited when Balboa made his erossing along its
northern end in 1513. Semiaquatic mammals such as the tapir, capy-
bara, and paca can remain there over the rainy season, but other
large mammals enter these swampy flats only during the dry season,
when it becomes for the Indians, a valuable hunting ground. The
larger oxbow lakes hold stagnant water, covered with green scum,
throughout the dry season, and outside the meander belts of the
larger rivers, water-bearing vines are the only safe source of drink-
ing water for the hunter in February, March, and April.

The largest of the monadnocks in this base-leveled area is the
Sanson ridge, the core of an anticline, which rises to a height of
1,800 feet at one point, according to the Air Chart.

The fact that this base-leveled surface still stands at tide level,
indicates isostatie stability from its completion to the present, and
this is borne out by the seismic records. Few shocks have been
recorded from Darien Province.

The eastern side of the arcuate lowland belt continues southward
to the head of the Tuira, where only a low ridge separates it from

No. 23] TERRY: GEOLOGY OF PANAMA 19

the broad flats of the Atrato, which are obviously its continuation,
but eut off from it by faulting of fairly recent date. Hildebrand
(1938) has noted that the fresh-water fishes of the Tuira (Pacific
drainage) resemble those of the Atrato (Atlantic drainage) more
closely than those of the Chagres .resemble those of the opposing
Pacifie slope.

The Pirri Range of central Darien Province, an asymmetric anti-
elinal fault block, separates the upper Tuira valley from the valley
of the Balsa to the west; the Balsa, in turn, is separated from the
Sambt: by another fault block of basement rocks, and another fault
block of mainly basement rocks separates the Sambi from the Pacific.
The Pirri block and the block between the Balsa and the Sambi
approach each other closely at the Colombian border, where the sum-
mits of each are beveled by a series of small level areas, so flat that
water stands in undrained depressions through a large part of the
year. The surface of these flats is around 4,000 feet on the Pirri
ridge and slightly less on the Altos de Aspavé across the Balsa valley.
These flats appear to be peneplane remnants, and if so, the peneplane
must have been cut following the mid-Tertiary folding which pre-
ceded the deposition of the Gatun (middle Miocene), since it is hardly
conceivable that an older peneplaned surface could have remained
level following intense asymmetric folding in the Tertiary. The inter-
val between the 4,000-foot mid-Miocene peneplane and the sea-level
Pleistocene peneplane of central Darien therefore marks for this area
the amount of uplift from mid-Miocene to Recent times. The upper
peneplane surface of the Pirri Range slopes gently northward and
more rapidly southward from a high point on the Colombian frontier
at the head of the Rio Salaqui 7° 44’ N., 77° 44’ W.) The elevation
of the high point, which is the summit of a monadnock on the old
peneplane, is 5,134 feet on the Aeronautic Chart. Other high points
in southeastern Darien are Cerro Pirri on the Pirri ridge at 4,973
feet, and Cerro Sapo on the ridge west of the Sambu at 4,264 feet.
The highest point in Darien is at the summit of Cerro Taecareuna on
the continental divide at 6,180 feet.

One of the least-known areas of eastern Panama is the mountain
block which divides the upper Bayano valley from the Pacific coast.
As the area from the crest of this divide to the Caribbean coast is
entirely Indian reservation, from which outsiders are excluded, and
since the coastal belt on the Pacific has been unattractive to oil
geologists, there has been no mapping of the intervening ridge.

Topographically it is an irregular mountain block rising to a
high point of 5,330 feet, elongated in a N. 30° W. direction and

20 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

apparently a structural continuation of the igneous divide between
the Sambti and the Balsa. The mountain ridge sinks to the north-
west and west and ends about five miles east of the mouth of the
Bayano. Like all the other physiographic provinces of eastern Panama,
it is gently arcuate, with convexity to the northeast. Its rocks where-
ever examined at its boundary are andesites, probably of the basement
complex, but on the upper Rio Congo, the writer saw boulders of
mica sehist in the stream channel.

Between the ridge and the coast is a coastal plain, varying from 3
to 10 miles in width with an irregular inner boundary. The under-
lying rocks of the plain, so far as identified, are Oligocene and
Miocene shales. Much of this coastal plain is mangrove swamp. The
gentle slope of its surface continues southwest beneath the ocean to
the Pearl Islands, and on to the edge of the continental shelf, 50
miles away.

San Miguel Bay and its eastward continuations, the estuaries of
the Tuira and Sabana rivers, as well as its northward fingers, the
estuaries of the Congo and the Cucunati, are the result of flooding
due to the rise of sea level, following the melting of the Pleistocene
icecap. The shores of these estuaries mark the limits of the meander
belts of the respective rivers during Pleistocene time. In the ease of
the Tuira, which carries all freight for the Tuira-Chucunaque basin,
the meanders of the old channel at the bottom of the estuary are well
known to the sailors of the launches running between Panama City
and Darien, and their curves are followed closely at low tide. A
stranger, watching with amazement the winding course followed by
the helmsman of such a craft on the wide estuary, would, if he mapped
the course, have a close approximation to the meanders of the Tuira
channel in Pleistocene time.

The geomorphology of Panama may be summed up briefly as
follows:

Eastern Panama—late stage of the erosion cycle, wide flats, mean-
dering rivers bordered by oxbow lakes in the Chueunaque-Tuira basin,
drowned lower valleys. Mountains in mature state, with high pene-
plane remnants near south border—major physiographic features
arcuate, with fault control on N. 30° W. and N. 25° E. lines. Block
faulting of mountains following folding. Evidence of recent isostatic
stability.

Central Panama—slightly earlier stage of erosion cycle. Streams
mostly consequents with fairly straight courses. No drowned valleys
on north coast and on Pacific coast small, mostly limited to ends of

No. 23] TERRY: GEOLOGY OF PANAMA 21

the Santiago plain. Arcuate form of physiographic features less ap-
parent than in eastern Panama. Block faulting shown in some areas.
Voleanic cones, Cerro Quema, El Valle, and San Miguel de la Borda
appear young. Coastal plain wide on Pacifie side, narrow on Carib-
bean. Continental shelf the same. Faulting of graben or rift type east
of Canal zone, faulting along coast of Azuero Peninsula and continu-
ing to the west.

Western Panama—early stage of erosion cycle. Narrow coastal
plain and wide mountain area in youthful stage. Streams mostly
consequents, but some meandering on coastal plain. Deformation of
Pleistocene peneplane in southwest indicates post-Pleistocene tectonic
activity. Pleistocene voleanoes, El Bart, and Santiago, and active
voleanoes to the west in Costa Rica, and seismic activity in western
part indicate lack of isostatic adjustment. Youthful mountain mor-
phology partly due to Pleistocene and Recent vuleanism.

IGNEOUS ROCKS

About one-half the surface of Panama is made up of igneous
rocks, most of which are of basic extrusive types. Crystallines are
for the most part confined to the region of the continental divide or
to other high mountain areas, where they appear as the result of
the erosion of a cover of andesite or basalt flows, a fact noted by
Hershey (1901) in central Panama, and by Lohman (1934) in Costa
Rica. Gabb (1875) considered the granite of Pico Blanco near the
Costa Rica-Panama boundary to be a post-mid-Miocene intrusion, but
Lohman (1934) disagrees. Wagner (1862) saw granite on the north
side of the divide near the head of the Gulf of San Blas. MacDonald
(1919) says the Chagres brings down granite float. The writer saw
granite on the head of Rio Indio north of El Valle, and has been
informed that it occurs in the Campana district, 20 to 25 miles west
of the Canal Zone. Hershey (1901), Taylor (1852), and Wagner
(1861) mention granite in the region adjacent to the north coast
near the Cocle-Veraguas border. Riddell (1927) says granite occurs
on the south slope of the continental divide, about 20 miles north of
La Mesa in Veraguas. In the Azuero Peninsula, granite float was
seen by Dunn (personal communication) on the head of Rio Quebro,
west of the Tonosi basin; and the writer collected a granite specimen
from an outerop about 10 miles southwest of Las Tablas on the trail
to Tonosi. The specimen was given to MacDonald (1937), who studied
a thin section and reported: “A light-colored, fine-grained, sodic
granite, which weathers pinkish. . . . The orthoclase and albite,
present in both large and small erystals, have been considerably

22 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

altered to epidote, calcite, and sericite. Some micrographic inter-
growths of quartz and orthoclase were noted. Magnetite appears as
a primary mineral, and is also secondary, associated with chlorite
from the alteration of hornblende. The alteration of this granite may
be due to later igneous intrusions.”

MacDonald’s conclusion that the granite was older than the adja-
cent basic rocks is of interest.

Light-colored quartz-bearing rock which may be granite or grano-
diorite has been seen near the head of the Rio Caldera in Chiriqui
Province by the writer. Syenite was reported by Wagner (1861),
and Hershey (1901) from the vicinity of Mineral, a few miles from
the coast of Veraguas on Rio Concepcion; and Gabb (1875) remarks:
“True granite rarely occurs, while Syenites are much more common.”

Acidie extrusive rocks in the form of rhyolite or rhyolitic tuffs
and ash, cover a large area in central Panama, south of the conti-
nental divide, mostly in the provinces of Coclé and Panama between
Chame and Anton. In the Canal Zone, Ancon hill was termed rhyolite
by MacDonald (1919), and the Panama tuffs are mainly rhyolitic.
Riddell (1927) says that Cobriza Peak in central Veraguas is rhyo-
lite and that a rhyolitic cap formerly covered Remancee hill.

Serpentine was seen by Dunn on the west side of the Azuero
Peninsula on the upper Rio Quebro, and he says that it was also
reported to him from Cerro Negrito on the coast of Montijo Bay.

Intrusive basie rocks are probably to be found over much of the
isthmus, but have been seldom reported. A specimen collected by
the writer in the Azuero Peninsula about 12 miles inland from Las
Tablas was sectioned and examined by MacDonald (1937), who re-
ported it a quartz gabbro, somewhat altered by later intrusives.

With the exception of the rhyolites of central Panama, there seems
to be little difference in the character of the extrusive igneous rocks
which overlie the erystallines. The dominant type is andesite; basalt
is next most common. Vuleanism seems to have been more or less
continuous from Eocene to Pleistocene time. There are no sediments
in which ash or tuff cannot be found; in many it constitutes a large
part of the rock. There appears to have been a particularly active
voleanie period in mid-Miocene time in connection with the uplift
and deformation which preceded and accompanied the deposition of
the Gatun formation in western Panama, but this is not true in Darien.
Since that time active vuleanism seems to have been limited to the
area west of the canal.

In the region between the canal and Sona, tuffs, ash, and lava are
included in, and interbedded with marine and terrestrial sediments

No. 23] TERRY: GHOLOGY OF PANAMA 23

to an extent that indicates that this area was the principal site of
voleanic activity in Oligocene and early Miocene times with the Pearl
Islands as another center, while Chiriqui and Bocas del Toro seem
to have been the principal center of late Miocene vuleanism. Eastern
Costa Rica and Chiriqui were active areas in Pliocene and Pleistocene
times; and western Costa Rica and Nicaragua are actively voleanic at
present. There seems to have been a steady westward progression of
voleanie activity since Eocene time. While late Eocene sediments
earry tuff and agglomerate in all parts of the country, the highest
ratio of included voleanic materials is in Darien Province, in the
eastern end of the country.

The monotonously uniform character of the andesite which forms
the larger part of the basement in Panama has discouraged the col-
lection of specimens for microscopic examination. A series of slides
made from specimens collected by the writer, mostly from islands in
Panama Bay and the Province of Darien, were examined by Dr. A. L.
Isotoff, at Stanford University in 1945. Fifty-four slides were classed
as andesite, 12 as diabase, and 8 as basalt. As the writer had made
some effort to collect from distinctive outcrops, the proportion of an-
desite is probably too low to represent truly the general character of
the igneous in this area. Some typical descriptions are quoted from
Isotoff :

T 3(b). Isla Saboga—Pearl Islands. West side. Andesite.
Phenocrysts of labradorite and augite in a groundmass filled with
microlites of andesine, grains of pigeonite and magnetite and alter-
ation products, notably carbonate and secondary quartz.

T 12. Isla Saboga—west side—at contact with sediments. Com-
position similar to the preceding, but with amygdules of calcite
and zeolite.

T 15. Isla Saboga—westernmost point. Andesite porphyry.
This rock has a coarser-grained groundmass than the preceding,
and this suggests it might be an intrusive phase.

T 21. Isla San Pablo. Andesite. A rock of trachytie texture
consisting of small laths of acidic andesine and a few larger laths
of labradorite. Dark minerals are absent in this section.

T 31. Isla Taboga at north end of village. Andesite (?). The
rock is strongly altered—the section shows a mosaic of secondary
quartz with sericite and alunite. There are vague suggestions of
the original porphyritic texture.

T 36. Isla Taboguilla near Pozo Maluco. Andesite. Trachytie
texture. Microlites are acidic andesine. Plagioclase phenocrysts
are altered completely to a mosaic of quartz and albite. Dark
minerals are represented by “ghosts” of chlorite and magnetite.

24

CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

T 43. Isla Otoque—N.W. side. Enstatite Andesite. Typically
andesitic texture. Microlites of andesine, grains of pigeonite and
magnetite with some residual glass from groundmass with pheno-
erysts of plagioclase, enstatite and augite.

T 52. Chiman. (Shore of Panama Bay about 60 miles east of
Canal Zone.) Hornblende andesite. Microfelsitic texture. Ande-
site with dominant green hornblende, partly fresh, partly changed
to ghosts of magnetite and chlorite. Some augite and fairly abun-
dant magnetite and apatite.

T 63. Rio Taimati. (South shore of San Miguel Bay about 10
miles from coast.) Andesite porphyry. Trachytie texture. Ande-
sine in groundmass and in phenocrysts. Much carbonate and
leucoxene.

T 69. Quebrada La Jira. (Tributary of Rio Congo—Darien
Provinee.) Biotite andesite. Microfelsitie groundmass with ande-
sine. Green Biotite is partly chloritized. Epidote, zeolites and
secondary quartz indicate an advanced stage of hydrothermal
alteration.

T 75. Alhajuela Highway 1 mile S. of Cruces trail crossing.
Lamprobolite andesite. Andesite with lamprobolite (basaltic horn-
blende) as the dominant mineral.

T 88. Setetule Mountain (Darien Provinee). Andesite ag-
elomerate. Hornblende and lamprobolite andesite.

T 108. Rio Cuasi—tributary of Rio Balsa—Darien Province.
Hypersthene andesite. Both ortho- and nonopyroxene are present.
The former appears to be optically negative and is therefore hy-
persthene. Very weak pleochroism indicates low iron content.

T 116. Cerro Mongorodo. Rio Balsa area—Darien. Andesite.
Microfelsitic groundmass. Plagioclase phenocrysts with inclusions
of groundmass. Dark minerals resorbed and indeterminable. Much
apatite and magnetite.

T 133. Volean—Chiriqui Provinee. Hornblende andesite.

T 137. Boquete—Chiriqui Province. Lava flow. Lamprobolite
andesite.

T 1. Isla Chitré—Pearl Islands. Diabase. A medium-grained
rock with subophitie texture. The labradorite is somewhat kaolin-
ized while the augite is altered completely to chlorite and ear-
bonate. There is much secondary quartz.

T 17. Isla del Rey—Pear] Islands. Punta Gorda. Diabase. A
coarse-grained rock consisting of labradorite and partly uralitized
augite. Chlorite, zeolites and magnetite are abundant in the inter-
stices between fairly fresh plagioclase crystals.

No. 23] TERRY: GHOLOGY OF PANAMA 25

T 60. Isla Iguana—San Miguel Bay—Darien. Diabase. Subo-
phitie texture. Laths of labradorite, augite, magnetite, chlorite.

T 73. Alhajuela Highway—one-half mile S. of Cruces trail
crossing, Canal Zone. Diabase. Dark minerals altered to chlorite.
Some jarosite is present.

T 20. Isla del Rey. On coast one-half mile west of San Miguel.
Basalt. The texture of the groundmass is intergranulate with
microlites of labradorite and grains of augite and magnetite. The
phenocrysts are of bytownite and augite, the latter being slightly
chloritized.

T 56. South of Chiman village. Basalt. Glomeroporphyritic
with subophitiec groundmass of labradorite laths and grains of
augite. Some chlorite.

T 68. Tucuticito—Rio Balsa, Darien. Amyegdaloidal basalt.
Labradorite microlites and grains of augite in intergranular
groundmass. Amyedules are filled with opal and chalcedony.

T 105. Quebrada Ciega. Head of Rio Balsa near Colombian
frontier. Basalt. Fairly coarse rock with labradorite and augite
in the groundmass and bytownite and augite in phenocrysts.
Intrusive (?). ;

T 107. Rio del Oeste—Altos de Aspave—Colombian frontier.
Basalt. Similar to T 105.

T 117. Rio Areti—tributary of Rio Balsa—Darien. Basalt.
Rather coarse grained with subophitic texture. Possibly intrusive.

In the Canal Zone, MacDonald found Ancon Hill to be a rhyolite
plug and ealled it, and other plugs and sills of basalt, probably Mio-
eene. In Chiriqui Province andesite occurs in the form of flow rocks
at the top of the lower Miocene underlying the middle Miocene, con-
sidered by Woodring and Olsson (personal communication) to be the
equivalent of the Gatun. This condition is well exposed along the
Rio David about six miles north of David and about two miles farther
north in a hill east of the river, where the stratigraphic position of
the andesite flow was confirmed by drilling operations. About 15
miles east of David, the Galera de Chorcha, a flat-topped hill, is capped
by andesite overlying lower Miocene shales. In Bocas del Toro Prov-
inee, along the shore of the Chiriqui lagoon and on several islands of
the lagoon, the Gatun lies upon andesite which is probably younger
than the lower Miocene, although the complete sequence is not always
present, and the Gatun lies directly on the basement andesite on the
flanks of the cordillera to the south, by reason of overlap beyond the
inner margin of the lower Miocene. It seems fairly certain, however,
that vuleanism was widespread at the close of lower Miocene time,

26 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

taking the form of tuffs and flows in western Panama. Dikes are
especially common in the Pearl Islands where they cut the shale series
which forms most of the northwestern part of the group. While the
fauna of these foraminiferal shales has not been determined, their
stratigraphic position and lithologic resemblance to the upper Oligo-
eene of the mainland leaves little doubt as to their age. They may
also include some lower Miocene. On Isla Chepillo at the mouth of
the Bayano River, no igneous appears at the surface, but the shales
are baked to a hard argillite, and the dome structure, together with
the baking, indicates the presence of an igneous plug at no great
depth. Numerous plugs, dikes, and sills break through the Oligocene
and lower Miocene of the coastal plain from David to Penonomé, while
on the Canal Zone their number and irregular distribution is mainly
responsible for the irregular topography noted by Hill and others.
Owing to the lack of later sediments than lower Miocene in much of
the coastal plain, this period of igneous activity can not be dated more
precisely. Along the Costa Rica border north of Brefion, boulders
of andesite occur lying on the surface of the peneplane cut across the
outerop of the Oligocene and lower Miocene shales, and accumulate
at the bottoms of the ravines and stream courses. Their source is un-
known, but they may have come from a mid-Miocene flow like that
observed near David, or they may be of later age.

Pleistocene vuleanism is represented by El Bart (Volean de Chiri-
qui), by Cerro Santiago, and presumably by a similar voleanie cone
at El Valle, about 40 miles west of the Canal Zone. Although much
smaller than El Bart, the El Valle cone is topographically similar,
with smooth slope drained by radiating box canyons, which have de-
veloped few laterals, and are obviously very young. Like El Bart,
it lies on the south side of the continental divide and close to it, and
apparently close to the contact of the Tertiary sediments with the
basement rocks. A single crater of oval shape, about four miles on
the longer diameter, is floored by lake deposits and drained by a tribu-
tary of the Rio Anton through a narrow canyon at the southwest end.
The wall rocks are rhyolite.

In the Gulf of Panama, off Chame Point, a group of islands of
which the largest are Otoque, Bona, and Estiva, enclose a caldera-like
circular area resembling that formed in the Sunda straits by the
explosion of Krakatoa in 1883. Otoque, the largest of the group, is
composed of andesite, apparently a part of the basement rocks, sur-
mounted at the north side by a ridge of bedded white chert and the
remnants of Eocene limestones. The andesites continue to the south
side of the island, where they front the supposed caldera, on the south

No. 23] TERRY: GEOLOGY OF PANAMA 27

side of which, a few miles away, is Bona, a steep hill about 650 feet
high composed of steeply dipping, nearly vertical ash and tuffs. Es-
tiva on the west and a few smaller islands occupy intermediate places
on the supposed former rim. A small plug of light-colored rock stands
at the north foot of Bona, and a specimen from this and from a large
bomblike mass at the crest were sectioned for microscopic examina-
tion. Isotoff’s report on them is as follows:

T 46 and T 47. Isla Bona. Indeterminable in sections—fine-
erained quartz rocks with chlorite, leucoxene, magnetite, and seri-
cite. Possibly altered andesite.

There is no means of determining the date of formation of this
ealdera, if such it is, but it might reasonably be considered as con-
temporaneous with the dikes and plugs in the Pearl Islands, some 35
miles away.

At various points along the shores and on the islands in San Mi-
guel Bay in Darien Province, thin-bedded tuffaceous shales, some
carrying foraminifera and some of them barren, are encountered in
thicknesses running into thousands of feet. Neither the top nor bottom
of the section is exposed, but the only other rocks exposed in the
adjacent mainland are andesitic flows and agglomerates, supposedly
belonging to the basement complex. These tuffs and shales have been
considered to belong to the Oligocene from their lithologie resemblance
to the known Oligocene near the Canal Zone and in the region of
Chepo. A slide made from a specimen taken at the mouth of the Rio
Cucunati was reported by Isotoff thus:

T 62. Ensenada Cucunati. Tuffaceous shale. Tests of forams,
erystal fragments and shards of glass.

Another from Rio Taimiti:

T 63. Tuff. Devitrified tuff with andesitic and crystal frag-
ments.

It would appear from Isotoff’s report as well as from field observation,
that the only regional difference is the absence of andesite from the
basement rocks near the Colombian border in Darien where nothing
but basalt was found.

METAMORPHIC ROCKS

True metamorphic rocks are rare in Panama. Gneiss has never
been reported. The writer has seen schist on the Rio Marea, a few
miles above the village of that name in Darien and as float in the

28 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

upper Rio Congo, also in Darien. Slate oceurs in central Los Santos
Province, and near the south coast of the Azuero Peninsula west of
Morro Puercos; and on the Rio Diquis in southern Costa Rica, 35
miles west of the Panama border. All these outcrops are small. Argil-
lite, apparently caused by baking of shale by flows or sills, occurs
near Morro Puercos; on the head of Rio Chiriqui north of Caldera;
in the Burica Peninsula on the upper Rio Blanco; and near Golfito
in southeastern Costa Rica. It occurs commonly as boulders or gravel
in the Rio Chiriqui Viejo, and in the Pleistocene conglomerate near
Puerto Armuelles. No metamorphic minerals are developed in it; much
of it might be called simply baked shale. There are many places where
Oligocene and Miocene shales have been baked by intrusive sills and
dikes, but in most eases the effect is limited to a few inches, rarely
more than a foot from the contact. It is possible that some of the
argillite boulders have come from such occurrences; however, the argil-
lite outcrops deseribed above are in the basement complex; they are
pre-late Eocene, perhaps Cretaceous. Woodring and Thompson (1949)
speak of “indurated fine-grained sediments that were probably origi-
nally fine-grained tuffs,” which occur in the basement complex of the
Canal Zone. These are probably of the same period as the argillites
described above.

Near the Rio Ocones on the south coast of Veraguas west of Morro
Puerecos, there are also black shales which are not indurated, but
which do not resemble the Tertiary sediments of the region. These
unaltered rocks also appear to belong to the basement complex of
Veraguas. There is also a small outcrop of marble farther east.

In general, the basement complex is extrusive voleanics, flows,
agglomerates, and tuffs, showing much deformation, but little meta-
morphism, and predominantly basic. The sedimentaries or altered
sedimentaries included with the lavas are probably not older than
Cretaceous. Some of them may be early or middle Eocene.

SEDIMENTARY ROCKS

At many places, mostly in Darien from the Sabana River west-
ward; on certain islands in the Gulf of Panama; at Bahia Honda on
the south coast of Veraguas; and on the Burica Peninsula, there is
found a stratified white, gray, blue, or green chert, which lies on the
voleanies of the basement complex where its base is seen, and under-
lies the Eocene limestone. In the Rio Sabana-Rio Congo area of
Darien, it is in some places interbedded with tuffs, but in general it
appears to be a separate unit. No fossils have been seen in it, and
its age is unknown. Olsson (1942) thinks it may be the equivalent

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No. 23] TERRY: GEOLOGY OF PANAMA 29

of the Guayaquil chert of Ecuador, which has been assigned various
ages from late Cretaceous to middle Eocene. It has been thought to
be a chemical deposit, associated with submarine eruptions.

CRETACEOUS

Although no description has been published, it is known that Cre-
taceous foraminifera have been found in northwestern Panama. It
is also possible that the argillites mentioned under Metamorphic Rocks
are of that age.

EOocENE

The oldest fossils described from Panama, according to Olsson
(1942), are of late Eocene age and belong to the Buicaru forma-
tion of Los Santos Province in the Azuero Peninsula. The rocks out-
erop near Punta Bucaru near the mouth of the Tonosi River, and
underlie the Tonosi valley, a fault basin about 15 miles wide and 35
or more miles long in the south-central part of the peninsula. The
exposed thickness approximates 2,000 feet, according to Olsson, and
it seems probable that it originally covered a much larger area on
both sides of the basin. Small exposures of Eocene occur along the
east shore of Montijo Bay on the west side of the peninsula. The
Azuero Peninsula Eocene is the only known outerop of that age be-
tween the Canal Zone and David, a distance of some 180 miles,
although Eocene may be concealed beneath younger rocks at some
intervening points.

The Bucaru formation begins with a voleanic breccia containing
worn fossil fragments, and with a limey cement. The large angular
voleanie fragments continue upward for some distance in the lower
part of the formation, indicating that the beginning of the invasion
of the sea was contemporaneous with the last phase of Eocene vul-
eanism. Following the fossil-bearing conglomerates are blue-green or
black shales with thin sandstone beds, with a total thickness of about
1,500 feet, and these are followed by about 500 feet of blue coarse
sandstones and sandy yellow limestones. This last section carried a
fauna mainly of foraminifera, while in the middle and lower parts
of the formation the fauna is mainly mollusean, and Olsson considers
it to be the oldest Eocene of Panama, equivalent to the Talaran, the
lower late Eocene of Peru. Typical fossils from this part of the section
are listed by Olsson as: Aturia peruviana Olsson, Venericardia tono-
stensis Rutsch, Noetiopsis woodringt MacNeil, Raetomya sp., Spisula
sp., Tellina sp., Cardiuwm ef. samanicum Olsson, Conus ef. peruvianus

30 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

Olsson, Lyria sp., Clavilithes sp., Xancus ef. peruvianus Olsson, and
Harrisonella ef. peruviana Olsson.

From the upper part, Lepidocyclina panamensis Cushman was col-
lected by MacDonald, with a still higher horizon containing Oper-
culina and echinoids. Olsson believes this horizon to be separated from
the Lepidocyclina beds by an unconformity. From collections by Ols-
son and Terry from the upper section, Vaughan (personal communi-
eation) identified Pseudophragmina (Proporocylina) ef. P. flintensis
Cushman, Operculinoides, Carpenteria, Gypsina, Helicostegina sp.,
apparently H. soldadensis Grimsdale, and Lepidocyclina (Pliolepi-
dina) panamensis Cushman, A and B forms.

The Canal Zone Eocene is described by Woodring and Thompson
(1949) as beginning with 1 to 3 feet of conglomerate, followed by 25
feet of medium to fine-grained sandstone, the upper part of which is
silty. Above this, the formation is made up of mudstone and siltstone,
which carries lenses of limestone, mostly thin, but in some places
reaching a maximum of 300 feet. The limestone lenses carry orbitoidal
foraminifera, including Lepidocyclina chaperi and LD. ef. pustulosa.
Woodring and Thompson (1949) give the Eocene of the Canal Zone
the name Gatuncillo formation and consider it to be the equivalent of
the Eocene of the Madden Lake basin described by Reeves and Ross
(1930) under the name Bohio. Reeves and Ross were not immediately
concerned with Eocene stratigraphy and indicated only that it is
divisible into two parts, “‘a thick series of hard thin-bedded fossili-
ferous limestone at its top, the rest of the formation consisting largely
of soft shale and clay, interbedded with lenses of similar limestone.
In addition, there is at the base a conglomerate consisting largely of
voleanie boulders.” Embich later collected from the shale of Reeves
and Ross’ lower division a fauna of small foraminifera described by
Coryell and Embich (1937), who gave the formation the name, Tran-
quilla shale. This name is discarded by Woodring and Thompson
(1949) because the type area is now covered by the waters of Madden
Lake, and no longer accessible. Coryell and Embich describe a fauna
of 46 genera and 64 species which they correlate with the McElroy
division of the Jackson (upper Eocene) of the United States, “because
of the presence of a variety of Textularva hocklyensis which is a guide
to the McElroy, and the characteristic species, Dentalina jacksonensis,
Eponides jacksonensis, Haplophragmoides dibollensis, and Robulus
alato-imbatus.” From the limestones overlying the shale of the Mad-
den Basin Olsson and Terry collected a fauna of orbitoidal foramini-
fera, which were studied by Vaughan (personal communication). They
include: Camerina striatoreticulata Rutsch, Carpenteria, Discocyclina

No. 23] TERRY: GHOLOGY OF PANAMA 31

georgiana Cushman, D. mariannensis Cushman, D. ef. D. minima
Cushman, D. (Asterocyclina) asterisca Guppy, Eodictyoconus, Amphi-
stegina ef. A. cubensis Palmer, Gypsina globulus Reuss, Heterostegina,
Lepidocyclina pustulosa forma toblert H. Douvillé, LZ. duplicata Cush-
man A and B forms, ZL. macdonald: Cushman, L. (Nephrolepidina) A
form, L. (Nephrolepidina) panamansis Cushman, A and B forms,
L. (Nephrolepidina) chaperi Lemoine & R. Douvillé, and Operculi-
noides ef. ocalanus Cushman. The rock contains an abundance of
Inthothamnium.

On the Rio Gatuncillo, near the village of New San Juan, Olsson
and Terry collected specimens identified by Vaughan: Hodictyoconus,
Cibicides, Carpenteria, Camerina, Operculinoides ocalanus Cushman,
O. soldadensis Vaughan and Cole, Heterostegina, Discocyclina (As-
terocyclina) georgiana Cushman, Discocyclina mariannensis Cushman,
Gypsina globulus Reuss, Amphistegina ef. A. cubensis Palmer, Lepido-
cyclina duplicata Cushman A and B forms, L. pustulosa H. Douvillé,
and L. macdonaldi Cushman.

The Madden dam basin is outlined by faults striking N. 70° E.,
which enclose an area some 14 miles wide and 25 miles long, including
the Canal Zone areas of the Gatuncillo formation. There is reason to
believe that the original area of marine Eocene was considerably
larger. The N. 70° E. system of faults is intersected by another set
striking N. 25° E. to N. 30° E., and at the east end of the basin, there
are fault contacts at various places which bring the higher members of
the Eocene formation into contact with the basement complex. Owing
to the difficulties occasioned by deep weathering and heavy jungle
cover, it is not easy to determine the presence, much less the amount of
displacement in these faults. However, south from the mouth of Rio
Chagres in Madden Lake to the continental divide, the Eocene shales
(Tranquilla or Gatuncillo) are apparently missing, whether by fault-
ing or overlap of the limestone section. On the continental divide
between the heads of Rio Enrique and Rio Chilibrillo, the orbitoidal
limestone lies directly on the andesite of the basement complex. From
specimens collected here and submitted to Vaughan, the following
were identified: Eodictyoconus, Camerina, Heterostegina, Gypsina,
Lepidocyclina ef. L. duplicata Cushman, Discocyclina ef. D. minima
Cushman, and Lepidocyclina (Nephrolepidina) ef. L. chaperi Lemoine
& Douvillé

Here there seems to be no doubt about the overlap of the lime-
stone beyond the limits of the shale.

In the foothill belt on the south flank of the continental divide,
the orbitoidal limestones continue to the east of the Madden Basin,

32 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

but Eocene has not been identified until the vicinity of Chepo, about
35 miles east of Panama City, is reached. Here on Rio Mamoni, the
writer collected the following, identified by Vaughan: Operculinoides,
Gypsina, Lepidocyclina pustulosa H. Douvillé. On the road east from
Chepo to El Llano: Eodictyoconus, Carpenteria, Gypsina, Operculi-
noides, Discocyclina minima Cushman, D. (Asterocyclina) asterisca
Guppy, Lepidocyclina macdonaldi Cushman, L. pustulosa H. Douvillé.
On Rio Terable: Operculinoides 2 spp., Discocyclina (Asterocyclina)
ef. D. asterisca Guppy, Pseudophragmina (Proporocyclina) sp., Lepr-
docyclina (Pliolepidina) sp., Helicostegina sp. close to H. soldadensts
Grimsdale. At Pena Tiburon on Rio Bayano above El Llano, were
collected Operculinoides, Lepidocyclina ef. pustulosa H. Douvillé, B.
form, and L. macdonaldi Cushman. At La Bobida on Rio Paja, a
tributary of Rio Bayano, Camerina, Operculinoides, and Lepidocy-
clina macdonaldi Cushman. In the Chepo-El Llano region the lime-
stones are lenticular and on Rio Platanal, Rio Uni, and Rio Terable,
small tributaries of the Bayano, clays and marls with occasional coarse
sandstones form the bulk of the formation in which a crustacean
(Zanthopsis terryi Rathbun), and some small mollusks, notably Am-
pullina ef. depressa Lamarck, and Potamides are common. Voleanic
tuff and ash overlie these beds and the transition to Early Oligocene
takes place in these tuffs.

The Eocene outcrop continues eastward and has been seen by the
writer as far east as Rio Tabardi, about 25 miles east of El Llano;
and it is known to exist above the mouth of Rio Iberti, about 10 miles
farther east. Between this point and Rio Chati in the province of
Darien, no exploration has been permitted by the Cuna Indians, but
the orbitoidal limestone reappears on the Chati and continues along
the flank of the continental divide to Rio Paya, on the Colombian
boundary near the head of Rio Tuira. It also occurs in Darien Prov-
ince on both sides of the Cerro Pirri, on Rio Sanson, Rio Conglon,
Rio Areti, Rio Cucunati, and Rio Sabana in central Darien Province,
on Rio Congo, and in the valley of Rio Sambt near the Pacifie coast.
On the coast it has not been discovered.

In central Darien Province, on Rio Pihuila, a tributary of Rio
Balsa, the formation is a sandy shale and sandstone, with Potamides
and Hemisinus. On Rio Corcona, a tributary of Rio Chico, in Chu-
cunaque drainage, the base of the Eocene is a dark shale with sand-
stone layers, carrying Lepidocyclina ef. chapert. In general, however,
the Eocene of Darien consists of hard, erystalline limestone with, in
the larger part, included voleanie matter, which locally runs to hun-
dreds, in some eases thousands of feet in thickness. On Quebrada Los

No. 23] TERRY: GEOLOGY OF PANAMA 33

Nunos, a tributary of Rio Sabana, the thickness of the combined ag-
glomerate, conglomerate, and limestone exceeds 4,850 feet, of which
about 1,650 feet is in the coarse voleanic clastics and interbedded lime-
stone lenses of the lower part, and about 600 feet of finer tuffs and
limestones, the uppermost 2,600 feet being thin- to medium-bedded
limestone with not much noticeable voleanic material. The base of
the section rests on well-bedded greenish chert, much deformed and
twisted. No fossils were collected, but it appears that the lower and
middle sections correspond to the Eocene and that the upper part
may be Oligocene.

On the Tupisa and Despreciado of the Chucunaque, the Eocene
begins with 850+ feet of dark shale and shaly sandstone carrying
orbitoids, followed by 2,540 feet of agglomerates, with a few thin
sandstones and conglomerates; and above the agglomerates, 220 feet
of clay, 420 feet of sandstone and sandy shale, 430 feet of limestone,
320 feet of sandstone and shale, and 900 feet of limestone and eal-
careous sandstone—a total of 5,580 feet which includes an unknown
amount of Early Oligocene, probably not over 1,000 feet. No such
thicknesses of Eocene, and no such amount of interbedded voleanies
are known elsewhere in Panama. Evidently Late Eocene vuleanism
was much more vigorous in Darien than in central or western Panama.

On Rio Congo a section exceeding 1,000 feet in thickness consists
mainly of coarse agglomerate, some boulders reaching 8 to 10 feet in
diameter, with a matrix of finer tuffaceous material. In this agglom-
erate appear occasional lenses of orbitoidal limestone. Here as in Los
Santos, the last of the great Eocene volcanic activity coincides with
the beginning of marine sedimentation.

In western Panama, recognized Eocene begins three miles north
of David, the capital of Chiriqui Provinee. This is about 100 miles
west of the nearest Eocene, on the shore of Montijo Bay. The inter-
vening sedimentary area of Chiriqui and Veraguas is surfaced with
Oligocene and Miocene, and the Eocene may underlie them, but is not
known to outerop.

The well-known David Eocene exposure near km. 12 on the Chiri-
qui National Railway is in a much-faulted area with tepid sulfur
springs which have created a swamp surrounding the small outcrop
of orbitoidal limestone from which Lepidocyclina panamensis, L. du-
plicata, and L. macdonaldi have been identified. Farther west, for a
distance of five or six miles, a more complete section is exposed on
various tributaries of Rio Platanal; and near the Costa Rica border,
on the Rio Blanco de Brefion, a small tributary of the Chiriqui Viejo,
an apparently complete section of late Eocene can be seen in the axial

34 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

part of a large anticline. Three limestone beds, separated by coarse
barren sandstones, yielded the following (identifications by Vaughan) :
Basal bed (lying on andesite) —EKodictyoconus, Camerina, Heteroste-
gina, Discocyclina sp. near D. minima Cushman, Lepidocyclina 2 spp.

Bed 2—Discocyclina sp., Lepidocyclina trinitatis (?), Lepidocy-
clina (Nepthrolepidina) sp., Lepidocyclina sp. Possibly a fourth spe-
cies of Lepidocyclina.

Bed 3—Lepidocyclina trinitatis (?) and L. (Nephrolepidina).

Above Bed 3 is another barren sandstone and then a conglomerate
with lime cement, carrying Lepidocyclina gigas and marking the base
of the Oligocene.

Twenty miles to the south in the Burica Peninsula limestone
forms almost the entire thickness of the Eocene. No fossils have been
collected, but the tests of orbitoidal foraminifera constitute a large
part of the rock which exceeds 100 feet in thickness and rests directly
on the andesite, or, in some places, on a thick chert.

On the north side of the continental divide, in Bocas del Toro
Province, the limestone includes much voleanic material, but the chert
is missing, the limestone lying directly on the andesite. The collected
material in the United States National Museum has not been studied,
but the fossils resemble those of the Chiriqui Eocene and the correla-
tion is accepted by geologists who have worked in both areas. The
Boeas del Toro Eocene extends westward into Costa Rica as does the
Eocene of Chiriqui.

The Eocene of the Isthmian region represents an invasion of the
sea over a region predominantly volcanic, or in some limited areas
with cherts. The limits of this Eocene sea can not be determined
with certainty. In eastern Panama, the Eocene sediments are found
bordering all the large areas of basement igneous, and small exposures
of infolded or infaulted Eocene can be found within those areas so
frequently as to leave little doubt that it once covered the entire
province of Darien. West of San Miguel Bay no Eocene is known in
Pacific drainage, except the narrow band along the foothills of the
continental divide, which ends at the Canal Zone. Eocene is not defi-
nitely known in the islands off the Pacific coast, but may be present
in small amounts on Isla del Rey.

In central and western Panama, no Eocene occurs in Atlantic
drainage between the Canal Zone and the basin of the Changuinola
River in Bocas del Toro Province, a distance of more than 200 miles;
while on the Pacific side an equal interval is broken only by the out-
crop on the Azuero Peninsula. While much of these intervening areas
is covered with younger sediments which may conceal Eocene deposits,

No. 23] TERRY: GHOLOGY OF PANAMA 35

it seems unlikely in a country so much folded and faulted and with
so many exposures of the basement rocks, that the Eocene could re-
main unknown if it were present. It is the writer’s conclusion that
the provinees of Coclé and Veraguas were mostly land areas in Kocene
time. The deposition of the late Eocene seems to coincide with the
dying phases of a vuleanism of which the greatest-activity of the
period was in Darien Province around the head of San Miguel Bay.
Practically all the Eocene is of shallow water deposition.

OLIGOCENE

Oligocene sediments are of two distinct types, marine deposits
laid down in waters of moderate depth, and terrestrial deposits, con-
sisting largely of volcanic clastics, with some terrestrial and shallow-
water marine sediments. The principal centers of voleanic activity in
Oligocene time were the Pearl Islands of Panama Bay (fig. 3), and
the shores of San Miguel Bay; and central Panama from the Canal
Zone to Montijo Bay. The voleanic elastics occur interbedded with

Geological Recoonaissance Map
of a part of the

PEARL ISLANDS,R.P

Tuffaceous sandstone Eg Agglommerate fod
Tuffaceous shale = Intrusives Be]

s ik Nautical, Miles 3

Figure 3. Geological reconnaissance map of a part of the Pearl Islands.

36 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

marine shales in the former area, and with lignites and other terres-
trial deposits in the latter. No satisfactory separation has been made
between the Oligocene and the underlying late Eocene, nor between
the Oligocene and the overlying early Miocene. In eastern Panama,
the base of the Oligocene probably lies near the top of the limestone
section, most of which is undoubtedly Eocene, but no collections from
this horizon have been studied.

The bulk of the Oligocene in eastern Panama consists of a mas-
sive brownish marl with numerous radiolarian spicules and much fine
voleanie ash. In the vicinity of San Miguel Bay, the voleanie mate-
rial is coarser and constitutes the bulk of the formation, but in the
Garachiné-Sambui basin, and the Tuira-Chueunaque valley, the radio-
larian ooze is more plentiful. In the Sambt valley geologists of the
Gulf Oil Company described the Oligocene as “a marly material which
is sometimes hard enough to be classed as limestone. Dark gray to
brown in color. Many foraminifera, and also radiolaria which have
been replaced by calcite. Much organic matter.”” Below this the sec-
tion changes to hard ecaleareous shale and fine dark crystalline lime-
stone, with the Eocene contact undefined. The equivalent Oligocene
section in the Tuira-Chucunaque valley is quite similar and has been
ealled the Aruza formation.

In the lower valley of the Bayano River, near E] Llano, the Ol-
gocene appears as a yellowish to brownish gray tuffaceous sandstone
and sandy tuffaceous shale with limestone lenses from which collections
made by Olsson and Terry yielded: Heterostegina panamensis Gravell,
Lepidocyclina canellei Lemoine and R. Douvillé, and Miogypsina cush-
mant Vaughan. Farther west at Rio Hondo, about three miles west
of Chepo, the same assemblage was found, and still farther west at
Rio Pacora, a collection by Terry gave Operculinoides, Lepidocyclina
sp., Nephrolepidina verbecki H. & H. T. Barker, Eulepidina sp. aff. L.
undosa Cushman.

On the old Spanish trail from Panama to Nombre Dios at Monte
Oscuro, a few miles outside the Panama City limit, Olsson collected
Gypsina, Heterostegina, Miogypsina, and Lepidocyclina sp. ef. L.
miraflorensis Vaughan. This locality is close to the Canal Zone limit
and the formation is largely voleanic material. It probably belongs
in the Bohio formation.

In the Zone, Woodring and Thompson (1949) describe the Bohio
aS massive or poorly bedded conglomerate, tuffaceous sandstone, and
tuffaceous siltstone. The coarse constituents of the conglomerate range
up to boulders six feet in diameter and coarse and fine matter is
mostly basaltic. Much of it is nonmarine, and silicified tree trunks

No. 23] TERRY: GEOLOGY OF PANAMA 37

occur in it. Fossils are rare, but Lepidocyclina canellei has been recog-
nized by Stewart from a locality near Darien station on the railroad.

According to Woodring and Thompson in the region of the Gail-
lard eut the Bohio is replaced by the Bas Obispo and Las Cascadas
formations, which are entirely voleanic, consisting of angular and
subangular fragments of andesite embedded in tuffs in the Bas Obispo,
and waxy and clayey altered tuff in Las Cascadas. The age determi-
nation is questionable. West of the Canal Zone, Olsson and Terry,
in a traverse from El Valle to Puerto La Tagua, at the southwest
corner of Gatun Lake, passed over a ten-mile stretch of volcanics,
lava flows, agglomerates, tuffs, and ash. A rude bedding could oceca-
sionally be seen, the dip being generally northward at a low angle.
Near the Rio Esterial terrestrial sediments appear, including coal. No
fossils have been collected from the coal-bearing section, but it is be-
lieved to be the equivalent of the lower Caimito, which Woodring and
Thompson (1949) consider early Oligocene in the adjacent Canal Zone
area. The entire region from the Canal Zone westward seems to have
been a voleanic island in Oligocene time. The Canal Zone includes
the fringe of these eruptive rocks, where they interfinger with sedi-
ments, in some places marine, in other places terrestrial. This band
of interbedded sediments and voleanies extends westward to about
80° 45’ on the Caribbean coast. It is hard to draw a contact, for the
inner edge of the sediments which are thus interbedded, as the line
is undoubtedly extremely irregular and could only be mapped after
thorough detailed field work. The writer made a trip up the Rio
Coclé del Norte to the mouth of thes Rio Toabre and from the canoe
could see no outcrops along the river other than the voleanics, but
sedimentary beds are present, as samples shown him along the way
included foraminiferal shales which had been baked at the contact
with andesitic lavas. From the air the region has the parallel-ridged
appearance of an area of tilted sediments.

In the Quebrancha syncline, east of the Canal Zone, Woodring and
Thompson (1949) divide the Bohio into a gritty sandstone lower
member and a voleanic upper member.

The late Oligocene of the Canal Zone is largely missing on the
Pacific coast and as far north as the Gaillard eut, but includes the
Culebra formation which is limited to the Gaillard cut and the im-
mediate vicinity. The age of the formation is a matter of dispute
among paleontologists, depending on personal opinion regarding the
diagnostic importance of the lepidocyeline species which in California
and the Canal Zone occur in the fossil assemblage which would other-
wise be regarded as Miocene; while in European and Atlantic coast

38 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

faunas, their presence is considered proof of Oligocene age. The Cule-
bra is placed by Woodring and Thompson at the top of the Oligocene,
but the larger part of the late Oligocene is missing, the Culebra rest-
ing on the Las Caseadas agglomerate. The Emperador limestone is
in the upper part of the Culebra, including the transition to definite
early Miocene. It is a light-colored, occasionally marly limestone, ap-
parently reefs, which are not continuous over more than a few miles,
and often much less so. Vaughan (1918) notes the evidently contem-
poraneous faunas of the Emperador and Culebra with the Antigua
Oligocene. The patchy occurrence of the Emperador has led to con-
fusion between it and other limestones.

On the Caribbean side of the Canal Zone, the late Oligocene is
included in the Caimito formation. Near the Darien radio station on
the railroad, the type section includes a basal conglomerate, which is
considered by Woodring and Thompson to be of Las Cascadas age.
The conglomerate consists of basaltic cobbles in a sandstone matrix
containing acidie tuff. The remainder of the formation in this locality
is divided into a lower member chiefly tuffaceous sandstone, with thin
limestone lenses, and a thicker upper member composed of tuff, ag-
glomeratic tuff, tuffaceous siltstone, and sandy tuffaceous limestone
lenses. The basal conglomerate is not fossiliferous, but in the lower
member Lepidocyclina canellei, L. vaughani, and other larger fora-
minifera occur, as also do corals. The upper member is less fossilifer-
ous, but carries Lepidocyclina caneller.

In the Quebrancha syncline just west of the Madden Dam basin,
Woodring and Thompson (1949) divide the Caimito into two mem-
bers, the Quebrancha limestone overlying the Bohio without uncon-
formity, and an overlying calcareous siltstone member which includes
some sandstone, while in the Madden Dam basin itself, they give the
Caimito a five-fold division, of which the three upper members are
placed in the early Miocene. The late Oligocene portion consists of a
caleareous sandstone member resting on the Bohio and an overlying
pyroclastic member containing a thick limestone lens carrying Lyro-
pecten condylomatus.

The same authors consider the entire Bohio of Reeves and Ross
(1930) as probably belonging to the Gatuncillo (Eocene), but from a
collection by Olsson and Terry in 1933, in the area now covered by
Madden Lake between the mouth of Rio Pequeni and Rio Puente,
Vaughan identified Lepidocyclina (EHulepidina) favosa Cushman, and
placed it in the Oligocene; Embich (personal communication) also
collected Lepidocyclina gigas from a nearby outerop. Apparently the
upper part of Reeves and Ross’s Bohio is actually Oligocene.

No. 23] TERRY: GHOLOGY OF PANAMA 39

In general, the Canal Zone Oligocene is terrestrial and mainly vol-
canic on the southwest side and increasingly marine in character as
one goes northeastward through the Madden Dam basin, suggesting
that there may have been an eastward outlet to the sea, which was
eut off by the mid-Miocene uplift and deformation. West of the Canal
Zone and south of the continental divide, rocks of voleanic origin pre-
dominate for some 20 miles or more to the vicinity of Capira; between
Capira and the coast an area of coal-bearing sandstone and shale
has been reported. The writer has not examined this area, but it
seems probable that the coal is of the same age as the Rio Indio coal
which occupies a similar stratigraphic position on the other side of
the divide. Vaughan (1918) states:

Dr. MacDonald collected fossil plants at Sta. 6840, about seven miles
northeast of Bejuca, near Chame, Panama, in a yellowish argillaceous sand-
stone that seems to overlap conglomerates and is believed to represent the
Caimito formation. Professor Berry records the following species from
this locality:

Guatteria culebrensis Berry, also Culebra and Gatun formations.
Hiraea oligocaenica Berry.

Hieronymia lehmanni Berry.

Schmidelia bejucensis Berry, also Culebra. As two of the four species
also occur in the Culebra formation, it appears that the formation in
which they were obtained is in age near the Culebra formation.

It is not known whether these coals are Oligocene or early Mio-
cene, but they appear to be definitely older than the coal of the Gatun
formation in Costa Rica, Bocas del Toro, and Chiriqui. The coal-
bearing sandstones outcrop at several places in, and on the borders
of the Santiago plain, and the rocks in which they occur carry large
amounts of volcanic ejecta, flows, tuffs, and ash.

South of the Santiago plain, on the east side of Montijo Bay, on
Rio Mariato, Condit collected Ampullinopsis ef. spencert Cooke, from
a shale overlying sandstones and conglomerates (Olsson, 1942). In
the United States National Museum, collection 7962 contains Turri-
tella ef. venezuelana, Nassa, Xancus, Pitaria, and Balanus, and Ols-
son considers it middle or late Oligocene (personal communication).
Collection 8467 from nearby contains Crassatella ef. berryt. Olsson
correlates the shale with the middle Oligocene of northern Peru and
with the Oligocene of Antigua, and places the underlying Montijo
formation as the equivalent of the Bojio. The coal-bearing sand-
stones of the Santiago plain thus would fall into late Oligocene
classification, although here as elsewhere in Panama, no sharp contact
can be drawn between the late Oligocene and the early Miocene. The

40 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

voleanic land area of Oligocene time apparently continued as far
west as the head of Montijo Bay, and probably farther. The Oligo-
cene island of central Panama was fringed by a low swampy coastal
region, on the surface of which shallow marine and terrestrial sedi-
ments were mingled with the ejecta from the voleanie island.

_ West of Montijo Bay, the Sona Peninsula is composed of igneous
rocks which the writer believes belong to the basement complex, from
the presence of stratified chert at Bahia Honda (L. G. Hertlein, per-
sonal communication). Stratified chert is known in Panama only
below the late Eocene. Near the lower course of Rio Tabasard about
20 miles west of Sona, coarse tuffaceous sediments with interbedded
lavas and voleaniec clastics of various sizes reappear. The formation
has not been studied and its age is uncertain, but at least a part of it,
if not all, is accepted as Oligocene by most geologists who have seen
it. There are no collections from this area, but United States National
Museum collection 6534, from a locality some miles north of San Felix,
contains Glyptostyla ef. panamensis, which suggests late middle or
late Oligocene to Olsson (personal communication). The outcrop
covers a belt 10 to 15 miles wide across Chiriqui Province to the east-
ern edge of the Pleistocene voleanics west of the David River, and
becomes finer grained westward. At the railroad line from David to
Boquete, which is close to the eastern edge of the Pleistocene voleanies,
the formation is a hard shale with considerable ash but no coarse
tuffs. The hardness is probably due to baking by erypto-vuleanism in
mid-Miocene time, as the region for miles around is cut by dikes and
plugs; and thick lava flows appear at, or close to, the contact between
early Miocene and middle Miocene. The Pleistocene voleanics cover
the region westward to Rio Chiriqui Viejo, near the Costa Rica border,
where the Tertiary sediments reappear. Here the Oligocene begins
with a conglomerate bed lying on late Eocene sandstone. The con-
glomerate is cemented with lime and earries Lepidocyclina gigas and
is followed by a shale section, then by two beds of limestone separated
by shale. The lower limestone bed carries a large selliform Nephro-
lepidina and the upper one has the same species and also Eulepidina
undosa (Vaughan, personal communication). In the shale a little
above these limestones are what appear to be specimens of Nummu-
lites, but identification is not complete as the material collected dis-
appeared in transit. The shales continue with numerous exposures
for a distance of 10 miles or more. They are usually gray in color
and carry numerous foraminifera, larger fossils being rare. They
resemble closely the Useari shale of Bocas del Toro and Costa Rica
and like the Useari, probably include middle and late Oligocene and

No. 23] TERRY: GEOLOGY OF PANAMA 41

early Miocene. In 1925 a well was drilled near David which began
in a lava flow of middle Miocene age, passed through some 150 feet
of lava, and an equal amount of Gatun sandstone and entered the
shale. No faunal record is available, but the writer has been informed
that the well passed directly from the Gatun into the Oligocene, no
early Miocene being found. There may be involved here the question
of diagnostic species, which is often a matter of dispute in the Isth-
mian region. No Oligocene has been recognized on the Burica
Peninsula.

On the Caribbean side the Useari has been studied by Olsson
(1922) from surface outcrops, and a considerable fauna has been
determined from well cuttings. As this faunal record has not been
published, it is included with the permission of the Sinclair Panama
Oil Company. Foraminifera from well on Columbus Island, Boeas
del Toro, R.P. (to depth of 7,790 feet) :

Amphistegina lessonii d’Orbigny Heterostomella cubensis

Anomalina sp. Palmer and Bermudez

Bolivina aenariensis (Costa) Marginulina basispinosa

Bolivina floridana Cushman Cushman and Renz

Bulimina bleeckeri Hedberg Marginulina subaculeata

Bulimina marginata d’Orbigny (Cushman)

Candorbulina universa Jedlitschka Marginulina wallacei Hedberg

Cassidulina subglobosa Brady Marginulina sp. “A”

Chilostomella oolina Schwager Nodosaria carinata d’Orbigny

Chilostomella ovicula Nuttall Nodosaria longiscata d@’Orbigny

Cibicides mexicana Nuttall Nodosaria raphanistrum (Linne)

Cibicides sp. Nodosaria vertebralis Batsch

Clavulina cyclostomata Nonion soldanii (d’Orbigny)
Galloway and Morrey Peneroplis sp.

Clavulina venezuelana Nuttall Plectofrondicularia californica

Cyclammina cancellata Brady Cushman and Stewart

Cyclammina sp. Planulina sp.

Dentalina sp. Pseudoclavulina mexicana Cushman

Discorbis bertheloti d’Orbigny Pullenia bulloides d’Orbigny

Ellipsonodosaria verneuili d’Orbigny Pyrgo murrhyna Schwager

Entosolenia marginata Montagu Quinqueloculina lamarckiana

Epistomena elegans d’Orbigny d’Orbigny

Eponides parantillarum Robulus calcar Linne
Galloway and Heminway Robulus cultratus Montfort

Gaudryina jacksonensis Cushman Robulus formosus Cushman

Glandulina laevigata d’Orbigny Robulus oblongus

Globigerina bulloides d’Orbigny Coryell and Rivero

Globigerina triloba Reuss Robulus sp. “B”

Globorotalia sp. Rzhekina sp.

Globobulimina pacifica Cushman Sigmoilina sp.

Gyroidina soldanti d’Orbigny Sigmoilina schlumbergeri

Haplophragmoides sp. A. Silvestri

42 CALIFORNIA ACADEMY OF SCIENCES

Siphonina tenuicarinata Cushman
Siphogenerina transversa Cushman
Sphaeroidena variabilis Reuss
Sphaeroidinella dehiscens

(Parker and Jones)
Spiroloculina alveata

Cushman and Todd
Textularia mexicana Cushman

[Oc. PAPERS

Textulariella sp.
Trochammina sp.
Uvigerina gardnerae Cushman
Uvigerina pygmaea d’Orbigny
Uvigerina rustica

Cushman and Edwards
Verneuilina sp.

In addition, Palmer (1923) determined the following species from
Nigua Creek, Panama [erroneously cited as Costa Rica in her account] :

Nodosaria soluta Reuss
Cristellaria cultrata Montfort
Cristellaria reniformis d’Orbigny
Frondicularia sp.

Nummulites costaricensis
(Palmer)
Vaginulina legumen Linnaeus

Porter (1942) collected from Amoura River, just above the mouth
of Useari Creek, the following additional species (determinations by

P. P. Goudkoff) :

Bolivina acerosa Cushman
Bolivina pisciformis
Galloway and Morrey
Bolivina rinconensis
Cushman and Laiming
Cassidulina crassa d’Orbigny
Cassidulinoides sp.
Cibicides cf. ungeriana d’Orbigny
Clavulina communis d’Orbigny
Dentalina cf. D. communis
d’Orbigny
Dentalina multilineata Bornemann
Dentalina roemeri Neugeboren
Eponides umbonata Reuss
Globigerina conglomerata Schwager
Lagena striato-punctata
Parker and Jones
Lamarckina sp.
Liebusella pozonensis var. crassa
Cushman and Renz

Marginulina subbullata Hantken
Nodosaria ewaldi Reuss
Nodosaria holserica Schwager
Nodosaria koina Schwager
Nodosaria camerina Dervieux
Planulina cushmani
Barbat and von Hstorff
Robulus barbati
Cushman and Hobson
Robulus mayi Cushman and Parker
Robulus cf. taettowata Stache
Saracenaria acutauricularis
Fichtell and Moll
Textularia mississippiensis
Cushman
Uvigerina cf. gardnerae
Cushman and Applin
Uvigerina hispida Schwager

This collection is from a section believed to be stratigraphically
lower than that at the oil seep on Useari Creek. According to Porter,
15 of the species are to be correlated with the lower Miocene, and 9
with the upper Oligocene. Porter proposes the name Amoura shale
for the section represented, leaving the question of member or forma-
tion status for future determination.

The Uscari represents the climax of a long period of erosion, begin-

No. 23] TERRY: GEOLOGY OF PANAMA 43

ning in late Eocene time and continuing with only minor and short-
lived regressions to mid-Miocene. At the end of the period, the land
of the present isthmian region must have been reduced to a group
of islands of a total area not exceeding one-half its present size—
perhaps much smaller. The total deposits of Oligocene and late Mio-
cene times are 5,000 feet thick or more over great areas and have a
total mass which seems to demand as a source a land area of much
greater size than the present isthmus. Although voleanic material
is present throughout, the bulk of the Oligocene and lower Miocene
consists of limy shales with considerable bituminous content. It ap-
pears to the writer that the presence of a considerable land area both
on the Caribbean and Pacific sides in regions now submerged must
be assumed for the greater part of the Oligocene and for much of
the lower Miocene.

The Useari is separated from the overlying middle Miocene by a
sharp erosional unconformity over most of the region. However, on
Columbus Island, Boeas del Toro Province, the overlying middle
Miocene is a shale with limestone lenses, with no basal conglomerate
or other lithologie indication of prolonged erosion. A well started
in lower Miocene beds was abandoned at 8,640 feet without encoun-
tering any significant change of formation. The bottom was in
middle Oligocene. According to the paleontologist the faunal record
indicates that the well passed through two thrust faults and perhaps
three, so that no accurate estimate can be made of the true thickness
of the formation. Estimates from measurements of surface outcrops
are subject to error arising from lack of continuity of exposures, -
and especially from the presence of faults, often unrecognized by
field geologists.

In the valley of the Reventazon River in Costa Rica, Branson
(1928) estimated 5,000 feet of Oligocene and early Miocene without
reaching the bottom of the section. This locality is about halfway
between Puerto Limon on the Caribbean coast, and the continental
divide. Branson’s Useari is mainly sandstones and conglomerates, with
two thick limestone members, while the Oligocene, though predomi-
nantly shale, also has several thick sandstones, some thin conglomer-
ates and several limestone beds. The whole series has a decidedly
shallow-water aspect as compared with the deep-water rocks of the
same age in Bocas del Toro.

MI0cENE

The early Miocene of the Garachiné region of eastern Panama
has been described as follows by the geologists of the Gulf Oil Com-

44 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS
pany: “Thinly bedded brown shaly material with lesser amounts of
more conspicuous brown limestones. The shale is somewhat argilla-
ceous, compacted ooze, made up largely of radiolarian remains com-
posed of amorphous silica. Series is bituminous; seeps heavy asphaltic
oil in several places. Forms small hills and ridges where exposed in
tilted structure.”

Oil seepages in the low swampy area bordering on the tidal flats
of Garachiné Bay undoubtedly come from this shale and limestone
section, though there are no exposures at the seeps. Farther inland,
these rocks are known as the dry seepage horizon, from their asphalt
seams. Wells of the Gulf Oil Company also encountered oil shows
in this horizon. Farther east, in the Tuira-Chucunaque basin, the
equivalent section is also oil-bearing and similar in lithology to that
described above. It grades downward without an erosional break
into the brown marl of the late Oligocene. In this area the upper
part is called the Aquaqua formation, the lower, the Aruza formation,
and the division corresponds approximately to the terms early Mio-
cene and late Oligocene, but no definite contact has been established.

From a well drilled by the Sinclair Panama Oil Company near
the Rio Yape, a tributary of Rio Tuira, the following fauna has been
determined :

Agathamina sp.
Amphistegina sp.
Astacolus crepidulatus Montfort
Anomalina ammonoides Reuss
Anomalina ariminensis d’Orbigny
Anomalina grosserugosa Giimbel
Bolivina aenariensis Costa
Bolivina argentea Cushman
Bolivina compacta Sidebottom
Bolivina dilatata Reuss
Bolivina floridana Cushman
Bolivina punctata d’Orbigny
Bolivina cf. pusilla Schwager
Bolivina cf. simpsoni Heron-Allen
and Farland
Bolivina schwageriana Brady
Bolivina tortuosa Brady
Bulimina aculeata d’Orbigny
Bulimina cf. affinis d’Orbigny
Bulimina buchiana d’Orbigny
Bulimina elegans d’Orbigny
Bulimina elongata d’Orbigny
Bulimina inflata Seguenza
Bulimina marginata d’Orbigny
Bulimina pupoides d’Orbigny

Bulimina pyrula @’ Orbigny
Bulimina cf. rostrata Brady
Bulimina sculptilis Cushman
Bulimina subornata Brady
Cassidulina crassa d’Orbigny
Cassidulina laevigata d’Orbigny
Cassidulina cf. subglobosa Brady
Cavulina parisensis d’Orbigny
Chilostomella ovoides Reuss
Cibicides culter Parker and Jones
Cibicides pygmaea Hantken
Cibicides ungeriana d’Orbigny
Cibicides (Truncatulina) sp.
Cribrostromoides sp.
Cyclammina sp.
Cyclammina cancellata Brady
Dentalina obliqua Linne
Ellipsoglandulina laevigata

A. Silvestri
Fissurina marginata Montagu
Frondicularia alata d’Orbigny
Gaudryina laevigata Franke
Gaudryina paupercula Cushman
Gaudryina rotunda Reuss
Gaudryina subrotundata Schwager

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No. 23]

Glandulina laevigata d’Orbigny
Glandulina rotundata Reuss
Globigerina bulloides d’Orbigny
Globigerina cretacea d’Orbigny
Globigerina conglobata, Brady
Globigerina dubia Egger
Globigerina cf. trilobata Costa
Gyroidina soldanii d’Orbigny
Haplophragmoides sp.
Haplophragmoides canariensis
d’Orbigny
Lagena sp.
Massilina sp.
Mucronina (hexacostata) d’Orbigny
Nodosaria costulata Reuss
Nodosaria consobrina d’Orbigny
Nodosaria cf. farcimen Reuss
Nodosaria filiformis d’Orbigny
Nodosaria hispida d’Orbigny
Nodosaria obliqua Linne
Nodosaria cf. pyrula d’Orbigny
Nodosaria radicula (Linne)
Nodosaria sagrinensis Bagg
Nodosaria soluta Reuss
Nodosaria vertebralis (Batsch)
Nonion boueanus d’Orbigny
Nonion pompilioides Fichtel and
Moll
Nonion scapha Fichtel and Moll
Nonion umbilicatula Walker and
Jacob
Orbulina universa d’Orbigny
Patrocles calcar (Linne)
Patrocles (Cristellaria) sp.
Patrocles cultrata (Montfort)
Patrocles mammilligera (Karrer)
Patrocles reniformis (d’Orbigny)

TERRY: GEOLOGY OF PANAMA 45

Patrocles rotulata (Lamarck)

Patrocles submammilligera
(Cushman)

Patrocles vaughani (Cushman)

Planulina ariminensis d’Orbigny

Plectrofrondicularia sp. (bicostate)

Plectrofrondicularia sp. (tricostate)

Plectrofrondicularia sp. (quadrate)

Polymorphina gibba d’Orbigny

Polymorphina burdigalensis
d’Orbigny

Pullenia sphaeroides d’Orbigny

Rheofax (?)

Reussella (?)

Rosalina (Discorbina) globularis
(d’Orbigny )

Rotalia beccarii Linne

Rotalia globularis (d’Orbigny)

Sigmoilina sp.

Siphogenerina sp.

Siphonina reticulata Czjzek

Sphaeroidina bulloides d’Orbigny

Spiroloculina sp.

Textularia abbreviata d’Orbigny

Textularia agglutinans d’Orbigny

Textularia gramen d’Orbigny

Textularia sagittula Defrance

Themeon (Polystomella) sagra
d’Orbigny

Trigonulina obliqua Seguenza

Triloculina sp.

Uvigerina asperula Chapman

Uvigerina canariensis d’Orbigny

Uvigerina pygmaea d’Orbigny

Uvigerina cf. tenuistriata Reuss

Virgulina squamosa d’Orbigny

Verneuilina cf. pygmaea Egger

The Aquaqua formation is bentonitic in some parts of the section,
and in the Yape well, bentonite beds were conspicuous aquifers. It
is believed that the forms listed above are entirely from the early
Miocene. The Aquaqua formation has been mapped as far north as
the Membrillo River, in the central Chucunaque valley, but the out-
erop grows smaller from the Tuira northward, apparently partly
because of progressive overlap of the middle Miocene, and perhaps
to erosion at the mid-Miocene uplift; but seven or eight miles west
on the Rio Sabana it is present apparently to a thickness of 2,000
feet or more. On the Pacific coast south of Garachiné Point, a nar-

46 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

row band of it appears standing on edge or dipping steeply in contact
with the basement rocks.

In central Panama the early Miocene has been carefully studied
only in the Canal Zone, where it is recognized by Woodring and
Thompson (1949) only in the region south of Gamboa, and in the
Madden Lake basin. In the Gaillard cut it is represented by the
Cucaracha formation which is mostly nonmarine, consisting of car-
bonaceous and lignitic shale, and massive greenish gray bentonitic
and tuffaceous clayey sandstone. There is usually a conglomerate at
the base. The bulk of the formation is the bentonitic clay.

The La Boca formation, known mostly from borings, according to
Woodring and Thompson, extends from the Gaillard cut to the Pacific
entrance of the Canal, and is chiefly silty or sandy mudstone. Con-
glomerate and sandstone are found in some bore holes in the lower
part. Near the base cream-colored coralliferous limestone of the type
of the Emperador interfinger with the clays of the Cucaracha forma-
tion. In the Pedro Miguel area the Pedro Miguel agglomerate overlies
the Cucaracha, but the lower part of it is apparently equivalent to
the upper part of the thicker Cucaracha section.

The Panama tuff is apparently a facies of the Cucaracha, a well-
stratified water-laid rhyolitic tuff with fragments of pumice. A few
foraminifera of Oligocene age have been found in the type region
near Diablo Heights, but these are probably inherited.

In the Madden Lake basin, the youngest rocks exposed are mas-
sive, fossiliferous tuffaceous sandstones, which form the foundation
of Madden dam. Olsson (1942) named the formation the Alhajuela
sandstone. These sandstones are increasingly caleareous downward
and have been divided by Woodring and Thompson (1949) into the
upper Alhajuela sandstone member and the calcareous sandstone
member. The latter contains so much lime that it might in some
places equally well be called a sandy limestone. The caves caused by
solution in this member were a serious engineering obstacle in the
construction of the Madden Dam, as some of them were of dimensions
ranging up to 100 feet. This member, according to Woodring and
Thompson, earries Turritella gatunensis, and is assigned to the early
Miocene. The Chilibrillo limestone which underlies it may be the
equivalent of the Emperador of the Canal Zone. It is considered to
be early Miocene by Woodring and Thompson. In the region between
Gamboa and the limits of the Canal Zone west of Gatun Lake, early
Miocene rocks are missing, according to Woodring and Thompson
(1949), but Jones (1950) disagrees.

West of the Canal Zone in central Panama, the early Miocene is

No. 23] TERRY: GHOLOGY OF PANAMA 47

probably represented only by voleanie ejecta, but lack of fossiliferous
sediments makes any dating questionable. Basic lavas and agglom-
erates form the surface from the Canal westward to Capira, beyond
which acidie rocks are found. The quartz sand beaches below these
acid rocks have been a much sought source of sand for concrete work
around Panama City. In the south wall of El Valle crater, well-
bedded rhyolitie tuffs, much resembling the Panama tuffs at Diablo
Heights, dip southward, and similar material with crossbedded tuffa-
ceous clays, sands, and gravels occurs in the vicinity of Penonomé.
Some of the sediments are diatomaceous, but no marine fossils were
seen. They are believed to be fresh-water deposits. Similar mate-
rial occurs along the road to La Pintada, a town about two miles
south of the continental divide and seven miles north of Penonomé.
About a mile north of La Pintada basic lavas appear, which are be-
lieved to belong to the basement complex, as between these andesites
and La Pintada is a chert outcrop, a rock which is known elsewhere
in Panama only from below the late Eocene at the top of the basement
complex. To the south and east of La Pintada on the trail to El Valle
are outcrops of rhyolite resembling the north wall of the El Valle
erater. The rhyolite flows also occur along the road from Penonomé to
Nata, where they can be traced westward to the Rio Grande where
andesite flows begin. The andesite flows strike northeast and dip
northwest, but the rhyolite flows and ash strike east-west and dip
south, apparently overlapping the andesite. The andesite flows form
the foothills of the continental divide toward which they dip. They
ean be traced westward to the vicinity of Canazas where they are
overlain by shale of probable early Miocene age, and on north to the
continental divide.

The structure is well shown in Hershey’s (1901) structure section.
(H-H). The writer has made many plane flights along this mountain
front and has checked the northward dip of the lavas and interbedded
sediments. It would appear that the andesite flows can not be younger
than early Miocene nor older than late Oligocene, and that they were
eroded and overlain by the rhyolite in the Nata-Penonomé-La Pintada
area. Shales of the Santiago formation of Hershey are considered
to be of early Miocene age by Woodring and late Oligocene by Olsson
(1942) The lava beds to the north overlie them and are without
much doubt early Miocene.

Collections made by Sinclair geologists in the vicinity of Santiago
are deposited in the United States National Museum, but have not
been studied. The collector’s notes are of some interest:

On the road from Santa Maria to Santiago—2nd hill of main divide 5

48 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

miles northeast of Santiago—close-textured shaly ls——Melanopsis, Cyrcana-
cea (?) like Inoceramus, fresh-water fauna. (U.S.N.M. Coll. 8465.)

Three-quarter mile southwest of Santiago on road to Montijo—calcareous
agglomeratic ss. Large Amusium, Ostrea—small, falcate, narrow sharp plica-
tion of entire periphery, Phacoides, Chione, Arca (Cunearca), Harpa, large
spatangoid echinoid. (U.S.N.M. Coll. 8466.)

Road crossing of Rio Martin Grande, one-quarter mile west of Santiago—
agglomeratic ss. Turritella cf. venezuelana, Oliva, Terebra, with large axial
costae on anterior half of whorl, 2 spiral bands on posterior half, Conus,
Triton, Natica small, Nassa, Glycymeris, Phacoides cf. anodonta, Veneri-
cardia, Pitaria, fragments of Crassatella cf. berryi. (U.S.N.M. Coll. 8467.)

These last beds appear to Olsson (personal communication) to be
borderline late Oligocene or early Miocene.

In Bocas del Toro Provinee, early Miocene shales form the upper
part of the Useari formation and have been described by Olsson
(1922), who lists a mollusecan fauna. Many of the foraminifera previ-
ously listed under the late Oligocene of Bocas del Toro also occur
in the early Miocene, but only three—Eponides parantillarum, Dis-
corbis berthelotti, and Spiroloculina alveata are apparently limited
to the Miocene in the recovery from the Bocas well.

South of the divide in Chiriqui Province, the early Miocene con-
sists of tuffaceous shales and shaly sandstones. From collections in
the United States National Museum, Olsson has identified the follow-
ing (personal communication) :

Arca macdonaldi Dall Dosinia cf. delicatissima

Arca veatchi Olsson Brown and Pilsbry
Architectonica sexlinearia Nelson Mactra cf. plicatella Lamarck
Chione propinqua Spieker Phos inornatus Gabb

Clementia dariena Conrad Turritella altilira Conrad

Conus multiliratus Bose Turritella cf. venezuelana Hodson

Crassatella berryi Spieker

A well drilled a few miles north of David is stated to have passed
directly from middle Miocene to Oligocene with no early Miocene
present. It is possible that this may be because of erosion preceding
the Gatun deposition, or the statement may be merely the paleon-
tologist’s opinion regarding the disputed position of the Oligocene-
Miocene contact.

On the Burica Peninsula, lower Miocene is possibly present. From
a collection on the upper San Bartolo River, Nonion grateloupi, N.
mesonense, Quinqueloculina lamarckina, and Virgulina pontoni have
been identified by Clift.

No. 23] TERRY: GEOLOGY OF PANAMA 49

In general the early Miocene of eastern Panama is an offshore
deposit of fine texture with some fine voleaniec matter; in central
Panama, it is shallow water or terrestrial with large amounts of vol-
eanic ejecta of all sorts, agglomerates, flows, tuffs, and ash; in western
Panama, it is a fine-textured shale of offshore type in Bocas del Toro,
somewhat sandier in Chiriqui and Costa Rica, and becomes con-
olomeratic in central Costa Rica west of Puerto Limon. The difficulty
in distinguishing the early Miocene from late Oligocene appears to
be about the same everywhere, indicating continuity of deposition in
all areas without regard to the character of the deposit.

MippLe Mi0cENE

The long period of continuous deposition from late Eocene through
early Miocene was broken in mid-Miocene time by uplift and ero-
sion in all parts of the Isthmian region. The uplift was accompanied
by vuleanism in western and central Panama, but apparently not in
eastern Panama. Folding and faulting were a part of the movement,
but much of the evidence is concealed beneath the deposits of middle
Miocene and later time. The angular unconformity between middle
Miocene and older sediments is sharply marked in the Burica Penin-
sula, where on the upper Rio La Vaca, Eocene limestone striking
N. 55° W. and dipping 65° NE. is overlain by Miocene conglomerate
and sandstone striking N. 75° W. and dipping 43° NE., and not far
away the Miocene with about the same dip and strike lies on the edges
of vertical Eocene limestone beds striking N. 72° W. Angular uncon-
formity between early and middle Miocene is generally much less
sharp, although often perceptible. As there has been much post-
Miocene folding, followed by erosion, the middle Miocene is now found
mostly in synelines, grabens, and basin areas, and is generally lacking
on anticlinals, horsts, or other areas of uplift.

The best-known middle Miocene is in the sedimentary basin cen-
tered round Gatun at the northern end of the Panama Canal. This
region because of its accessibility and economic and strategie impor-
tance has long been the object of study, and as it has not been much
affected by post-Miocene tectonic movements, the sequence, thickness,
and character of the beds has been well established. The basin is
gently arcuate, opening to the northwest and the strike of the basal
contact varies from nearly due north-south on the east side of the
basin to about N. 70° W. at the west side. On the east side, the
Gatun rests on the basement rocks, but on the southeast, south, and
southwest sides it lies on the late Oligocene (lower Caimito), or early
Miocene, according to Jones (1950).

50 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

Jones describes the Gatun as ‘“‘mudstones, siltstones, conglomerates
and tuffs, all thickly and massively bedded. The siltstones, sandstones,
and conglomerates are variably marly and tuffaceous, highly fossili-
ferous and massively jointed. . .. The tuffs are uniformly grained
siltstones and claystones except for local streaks, sparsely scattered
with pumice pebbles and cobbles. The formation has a thickness
known to exceed 1,400 feet and probably much more.”

Olsson (1942) divides the Gatun into three parts, a lower and
upper member of marine, highly fossiliferous sandstones, shales, and
argillaceous limestones; the middle member tuffaceous sandstones, or
beds of fuller’s earth with plant remains, only rarely containing ma-
rine fossils. He cites the principal fossils of the base as Pecten ga-
tunensis Toula, Arca dariensis Brown and Pilsbry, Clementia dariena
Conrad, Antigona caribbeana Anderson, Conus molus Brown and
Pilsbry, T'urritella gatunensis Conrad. At the Gatun spillway, he
finds underneath this a brown, gray, or black tuffaceous sandstone,
with lignitic material and plant remains, and carrying a few marine
fossils, such as Bittiwum, Cerithium, Conus, Arca, Tellina, and Nucula.
This series he assigns to the Caimito. Keen and Thompson (1946)
and Woodring and Thompson (1949), however, include it and other
still lower beds in the Gatun.

Keen and Thompson (1946) list from the lowest exposed Gatun,
“a subgenus, Bornia (Temblornia), known elsewhere only in the
Round Mountain silt (Temblor) of California. Cancellaria (Aphera)
islacolonis Maury, the zone fossil of the Cereado formation of His-
paniola, occurs somewhat higher, in the middle part of the lower
Gatun. Therefore, the lower part of the Gatun may be in part older
than middle Miocene.”

In eastern Panama, two outcrops of middle Miocene have been
mapped, a small area in the Sambit basin south and east of Garachiné,
and a much larger area in the Tuira-Chucunaque basin in eastern
Darien. In the Tuira basin the middle Miocene is in general divisible
into three parts, a lower member of conglomerate and sandstone with
small limestone lenses, a middle member of shale and shaly sandstone,
and an upper member of limey sandstone with limestone in thin beds
or lenses. The upper member is the most fossiliferous and carries a
fauna closely related to that of the Mount Hope section of the Canal
Zone Gatun. The sandstone and limestone of this member stand up
strongly against erosion, form ridges or cliffs along rivers so that its
outcrop is easily followed. Its distinctive appearance has led to its
being given member status under the name Pucro, the other two mem-
bers being grouped as lower Gatun. The fossils collected by the Sin-

No. 23] TERRY: GHOLOGY OF PANAMA 51

clair party of 1923-24 have not been carefully studied, but among
the commoner forms in the Pucro are:

Arca chiriquiensis Gabb Melongena consors Sowerby
Cancellaria dariena Toula Murex messorius Sowerby
Cancellaria solida Sowerby Panopea reflexa Say
Fasciolaria gorgosiana Pitaria gatunensis Dall
Brown and Pilsbry Turritella robusta Grzybowski

Malea camura Guppy

The conglomerate at the base of the lower Gatun has a thickness
of about 300 feet near the Colombia border, but increases northward
reaching a maximum of about 1,900 feet on the Rio Chico, the south-
ernmost tributary of the Chucunaque. There the conglomerate is
extremely heavy at the base, containing boulders up to six feet in
diameter and thins out rapidly in all directions. It apparently is a
delta deposit and probably indicates the position of the mouth of a
large and vigorous river of middle Miocene times. The lower Gatun
sandstone, while richly fossiliferous is perhaps less so than the Pucro.
Heavy-shelled mollusks are plentiful in the lower member, with fora-
minifera and thin-shelled mollusks in the shale above. Leaves and bits
of wood or chareoal are common in the shale, which in many places
has a greenish cast. In spite of the presence of much vegetable matter,
the Darien Gatun is not lignitie like that of Chiriqui and Bocas del
Toro. Attempts to measure the thickness of the middle Miocene of
the Chucunaque-Tuira basin have encountered the usual difficulties,
massive bedding in the sandstones, discontinuous outcrops in the shales,
and numerous faults, which are difficult to evaluate and often are
passed unseen by geologists who confine their observations to the
rivers. A probable maximum thickness for the lower Gatun is 3,300
to 3,500 feet, and for the Pucro 1,500 to 2,000 feet, but the average
amounts for each member would be somewhat less.

The middle Miocene represents transgressive overlap in the two
lower members and off lap in the Pucro, continued in the overlying
Chucunaque formation of late Miocene and perhaps Pliocene age. In
the Sambi basin, the middle Miocene is less well known. Its thickness
is estimated at 2,700 feet with a sandy conglomeratic limestone at the
top, composed largely of oyster and pecten shells, probably corre-
sponding to the Pucro and shales and sandstones below. There is no
evidence that the two areas, Sambti and Tuira, were ever in commu-
nication with each other. There was no vuleanism in these areas in
mid-Miocene time.

In western Panama, the deposition of the middle Miocene was
preceded and accompanied by widespread vulcanism, which has left

52 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

a record in the form of dikes, flows, and plugs, as well as much tuffa-
ceous matter included in the sediments. In addition to the marine
beds, terrestrial deposits including a considerable amount of low-
grade coal and lignite occur in Bocas del Toro and the Caribbean side
of Costa Rica, and to a lesser extent in the foothills of the cordillera
in Chiriqui and on Isla Muertos off the Pacific coast. In Boeas del
Toro the coal beds are found in several of the islands off the coast,
in the Valiente Peninsula, and in the headwaters of the Changuinola
River, and continue in the hills on the inner side of the coastal plain
in Costa Rica. They apparently lie in the upper part of the forma-
tion and may not be represented by contemporaneous marine deposits
except offshore.

The middle Miocene in western Panama has not been studied as
closely as in central and eastern Panama, and is less well known.
The formation in general carries a fauna closely related to that of
Gatun. The mollusks have been described by Olsson (1922). Coarse
conglomerates occur, not only at the base, but throughout the forma-
tion, even at the top, where they are transitional with the Pliocene
conglomerate; shales are present but not so plentifully as in other
parts of the country. Sandy lenticular limestones are common, and
in the coastal belt coral reef limestones, usually of small dimensions,
occur. The larger part of the formation is coarse gray tuffaceous sand-
stone derived mainly from the voleanies of the basement complex and
the andesite flows which form the base of the Gatun in many places.
Black sand beaches, composed largely of magnetite, occur in some
places where the Gatun is furnishing most of the sediment brought
down by the rivers. On Isla Colon (Columbus Island) and Isla Basti-
mentos (Provision Island) the base of the Gatun is a shale (Basti-
mentos shale) which interfingers with a coralline limestone (Minitimi
limestone). No conglomerate is present, but there is probably an
erosion interval at the base of Minitimi-Bastimentos formation. The
underlying Conch Point shale (lower Miocene) resembles the Basti-
mentos shale so closely that field geologists have had great difficulty
in separating them. Both are massive, poorly bedded, soft, gray clay
shales, which weather so rapidly that fresh exposures are rare. On
some of the other islands and on the Valiente Peninsula at the eastern
end of Chiriqui Lagoon, the base of the Gatun is basaltic or ande-
sitic flows.

The middle Miocene of Chiriqui is mostly concealed by younger
rocks, principally by the voleanie ejecta of El Bart. An area west
of David shows about 500 feet of section mostly sandstone, but because
of low dips, and massive bedding, and a great deal of faulting, the

No. 23] TERRY: GEOLOGY OF PANAMA 53

actual thickness present is only approximately known. Cross-bedded,
poorly consolidated sandstones, and soft sandy shales carrying a
considerable amount of vegetable remains, make up the visible part
of the section. Fossils collected from the area have not been carefully
studied, but field workers have agreed that they are closely related
to those of the Canal Zone Gatun. On the Burieca Peninsula, the
Miocene is transitional with the Pliocene, and over a range of some
3,000 feet of section, foraminifera, which in the United States are
considered diagnostic for each of the two periods, are intermingled.
This condition apparently includes both late and middle Miocene,
and the resulting confusion will probably not be disentangled for
many years to come. A fauna collected from various stations in Rio
San Bartolo, near Puerto Armuelles, and determined by W. O. Clift,
is appended:

Bolivina sp. Globigerina sp.
Bolivina cf. acerosa Cushman Globorotalia menardii (d’Orbigny )
Bolivina cf. alazanensis Cushman Gyroidina soldanii d’Orbigny
Bolivina interjuncta var. bicostata Marginulina pediformis Bornemann
Bolivina malkinae Nonion grateloupi (d’Orbigny )
Coryell and Embich Nonion mesonense Cole
Bolivina marginata Cushman Nonionella auris (d’Orbigny )
Bulimina inflata Seguenza Nonionella miocenica Cushman
Bulimina pupoides d’Orbigny Nonionella miocenica var. stella
Buliminella elegantissima Cushman
(d’Orbigny ) Planulina ariminensis d’Orbigny
Candorbulina universa Jedlitschka Pyrgo sp.
Cassidulina californica Quinqueloculina lamarckiana
Cushman and Hughes d’Orbigny
Cassidulina cf. crassa d’Orbigny Quinqueloculina seminula Reuss
Cibicides isidroensis Rotalia caloosahatcheensis Cole
Cushman and Renz Robulus oblongus
Cibicides refulgens Coryell and Rivero
Denys de Montfort Saracenaria acutauricularis
Cibicides sinistralis Fichtell and Moll
Coryell and Rivero Textularia sp.
Cibicides sp. Trochammina sp.
Eponides coryelli Palmer Uvigerina beccarit Fornasini
Gaudryina soldanensis Uvigerina pygmaea d’Orbigny
Cushman and Renz Valvulina oviedoiana d’Orbigny
Globigerina bulloides d’Orbigny Virgulina pontoni Cushman
Globigerina concinna Reuss Virgulina sp.

Globigerina triloba Reuss

The stream crosses outcrops of various formations from Eocene to
Pliocene, as can be seen from the map.

54 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

Upper MIOCENE AND PLIOCENE

As noted in the preceding paragraphs, the late Miocene and Plio-
cene of western Panama can not at present be distinguished by the
fossils, owing to the overlap of diagnostic species. A fauna collected
by the writer was determined by Coryell and Mossman (1942) as.
Pliocene. Other paleontologists, however, regard it as late Miocene,
and a similar condition exists with regard to the Toro and Chagres
formations of the Canal Zone and the Chucunaque formation of
Darien. In all three cases, the formations in question overlie middle
Miocene beds conformably, and with no evidence of a persistent ero-
sion interval, although there may be small local breaks. The Chagres
formation has been described by Jones (1950) and by Woodring
and Thompson (1949). It is a shallow-water marine sandstone of
which a limy phase is given member rank under the name Toro. It
is limited to a zone 7 to 10 miles in width along the coast west of the
Caribbean entrance to the Canal Zone. It narrows westward and
apparently disappears at some point within the next 15 miles. Ac-
cording to the mapping by Jones, it overlaps the Gatun increas-
ingly westward.

In the Tuira-Chucunaque basin in eastern Panama, the youngest
consolidated sediments are a series of sandstones and shales carrying
a marine fauna, mainly foraminiferal. It has been correlated with
the Chareo Azul of Coryell and Mossman (1942) and is thus involved
in the same age controversy. It overlies the Pucro sandstone of upper
middle Miocene age apparently conformably, beginning with a mas-
sive cross-bedded sandstone followed by gray foraminiferal shales, and
at the top is again sandy. It oceupies the trough of the long narrow
synclinorium stretching from Chepo to and beyond the Colombian
border, and in central Darien occupies a low swampy area, much of
which has been peneplaned or baseleveled. Where outerops occur,
the formation is seen to have been deformed by folding and faulting,
apparently prior to the peneplanation. No material of fresh volcanic
origin has been noted. An interesting feature is a narrow band of flat
chert pebbles near the base. Since chert is known to occur only below
the Eocene at the base of the sedimentary column, it would seem that
this occurrence represents erosion of a chert horizon at some point
within the “forbidden land” of the Cuna Indian reservation, as chert
is not known south of Membrillo. The Chucunaque is a normal marine
off-lap deposit, and represents the final withdrawal of the sea from
this part of the Isthmian region. It should be noted that the forma-
tion is not known in Darien outside the Chucunaque basin, but that
its greatest width is at the south end of the basin, suggesting that it,

No. 23] TERRY: GEOLOGY OF PANAMA 55

like the conformably underlying Puero, once extended to and beyond
the Colombian border. However, the paleontological correlation with
the Chareo Azul suggests that the final connection of this arm of the
sea may have been with the Pacific rather than the Caribbean. If
this arm of the sea were simply cut off and left to dry up, salt and
gypsum deposits would be expected, but have not been reported, nor
is the fauna depauperate, so far as known. .

In Boeas del Toro and adjacent Costa Rica, upper Miocene has
not been differentiated, but it may well be present. On the Pacific
side of western Panama, the Chareo Azul formation, considered to
be Pliocene by Olsson (1942) and by Coryell and Mossman (1942)
apparently includes as much or more Miocene than Pliocene. A. D.
Brixey, Jr., in a report on foraminifera from a well drilled near
Puerto Armuelles makes the following comment:

From the surface down to 1900 feet the foraminifera show closer affinities
with Pliocene age (Charco Azul) than to Pleistocene species of the Armuelles
formation. The marked absence of Miliolidae and Textularidae from 10 to
100 feet especially would tend to support a Pliocene (Charco Azul) age for
the upper part of the Corotu well. The presence of rather abundant Valvu-
lineria inflata, Bolivina costata var. bicostata, Buliminella constans cf. var.
basispinata, and Bulimina denudata also substantiate this belief.

Due to the overlapping range of certain foraminifera species, the contact
between the Miocene and Pliocene can not be sharply defined, either by
changes in lithology or by the distribution of foraminifera. In addition to
the species mentioned above which are Charco Azul types, other species
were found which point to Pliocene strata down to at least 1900 feet. At
1900 feet, a well-preserved large Robulus americanus var. grandis showed
strong resemblance to R. americanus cf. var. grandis which occurs in the
Bowden formation of Jamaica. This occurrence is especially interesting be-
cause R. americanus cf. grandis was the only species more typical of the
Atlantic-Caribbean middle Tertiary faunal zone, the other species being more
characteristic of the Pacific coast middle Tertiary. One from the upper Mon-
terey shale of California (Nonionella cf. mniocenica), was found at 1484 and
1720-1750 feet. Since only two specimens of N. miocenica were found, there
are two explanations for the occurrence: (a) either the form was in a section
of reworked sediments, or (b) the range of this species is greater than origi-
nally believed. It is significant, however, that N. miocenica was the only
typical Miocene species occurring between 1485 and 1750 feet. One of the
shortcomings in using foraminifera for correlation studies is that quite often
they appear as reworked specimens, having been moved by currents and/or
waves from different ecological zones or from different horizons.

A Mio-Pliocene age is given the section between 1900 and 5400 feet, due
to the presence of foraminifera which were characteristic of both Pliocene
and Miocene age sediments. Three species believed by Kew to be character-
istic of the lower Pico formation, lower Pliocene, of California were found in
the section between 5290 and 5300 feet. These species were Gyroidina soldani
var. rotundimargo, Bulimina pagoda var. hebespinata and Virgulina cf. no-

56 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

dosa. In the same section the following Miocene forms were identified: Nodo-
generina advena and Baggina cf. cancriformis, Nodogenerina advena, first
recognized in the lower Mohnian, Luisian, Relizian, and Saucesian of Califor-
nia, would indicate an upper middle to lower middle Miocene age. Baggina
cancriformis is typical of the lower Monterey (lower Relizian and lower
Modelo shale of Las Sauces Creek) of California.

Definite Miocene species begin at about 5400 feet and continue to 7790
feet where the last microfossils were encountered. These species include the
following: Bolivina aenariensis (which first appeared in the Mio-Pliocene at
4540 feet), Cassidulina margareta, two additional occurrences of Nodogene-
rina advena, Uvigerinella cf. californica, U. obesa and Virgulina floridana.
The last foraminifera identified in Coroti No. 1 were a broken Bathysiphon
sp. and a poorly preserved Bolivina sp. which were both found at 7770 feet.
(Private report by A. D. Brixey, Jr., to Sinclair Panama Oil Co., 1949.)

The fauna as determined by Brixey is as follows:

Depth in Feet
Mio-
Plio. Plio. Mio.
Angulogerina angulosa Williamson _........ 180— 190

Angulogerina carinata Cushman ................ 110-— 150
Angulogerina occidentalis Cushman _........ 6050-6060
Anomalina grosserugosa Gumbel ................ 180-1120
ANOM GUNG SD wes ee ee ee
Baggina cancriformis Kleinpell....... 5410-5420
BOlWinonGavendsCushiman ese 5410-5420
Bolivina aenarieniss (Costa) ............. Rane 2 hs 4540-4550 5420-5440
Bolivinaxyalatan(Sesuenza)) ieee 1435-1860 2400-2410
Bolivina costata var. bicostata

GiOrbigniy, fs. 5:te2 sawn oe ey ea ea 0-1750 3220-5300
Bolivina dattiana

Conyellvand) Mossmanyee ees 110-— 190
Bolivina foraminata Stewart ..................-..... 2000-5300
Boliving jloridang Cushman =2. 2.022 5410-5475
Bolivina interjuncta Cushman _................. 0-1900 4780 5440
Bolivina marginata Cushman ....................- 5410-5440
Bolivina cf. pomposa

Coryell and) Mossman 0-— 120
Bolivina cf. punctata d@’Orbigny _.................. 6340-6400
Bolivina cf. simplex

iPhlegersands arke ries eee Caehe 6730-6790
Bolivina sinuata var. “B”

Gallowayaand = Wissler ses eee 4790-5300
Bolivina subadvena var. spissa

@ushmand 2 cee. ees Sn ae 1435-1750
Bolivinagusp:: eee ee eee 6850-7770
Bulimina affinis d’Orbigny ...................-...----- 0-— 10
Bulimina cf. denudata

Cushmanvand Parkers eee 1235-1900 4010-5300
Bulimina elongata d@’Orbigny ........................ 5430-5440

No. 23] TERRY: GEOLOGY

Bulimina inflata Seguenza
Bulimina marginata d’Orbigny
Bulimina cf. pupoides d’Orbigny
Bulimina pagoda Cushman
Bulimina pagoda cf. var. hebespinata
R. E. and K. C. Stewart
Buliminella curta Cushman
Buliminella curta var. basispinata
Stewart
Cancris cf. panamensis Natland
Cassidulina californica
Cushman and Hughes
Cassidulina cf. cushmani
R. E. and K. C. Stewart
Cassidulina margareta Karrer
Cassidulina cf. pulchella d’Orbigny
Chilostomella czjzeki Reuss
Chilostomella cf. ovoidea Reuss
Cibicides americanus (Cushman)
Cibicides cf. hodgei

Cushmanjands Schenck

Cyclammina cancellata Brady
Dentalina cf. soluta Reuss

Globigerina bulloides d’Orbigny
Globigerinoides cf. sacculiferus Brady
Globigerinoides triloba Reuss

Globorotalia menardii d’Orbigny

Gyroidena soldanii d’Orbigny
Gyroidena soldanii var. rotundimargo

sulcata
and Jacob

Lagena cf.
Walker
Lagena sp. “A”
Lagena sp. “B”
Nodogenerina advena
Cushman and Laiming

INODOGCMETUNG SDs rea ee eee
INIOW@OS gl UES Date ee ee ee ee

Nonion costifera Cushman

INORVONTUNCTST MA CUShiays eee

Nonion scapha Fichtel and Moll
Nonionella cf. miocenica Cushman
Orbulina universa d’Orbigny
Planulina ariminensis d’Orbigny

ET SOLE GEN OS Ds ee
Epistomina bradyi Galloway and Wissler....
Globigerina conglomerata Schwager ...........
UEC LULU SD mc ae eee Sees ee ee

FLODLOP ROG MOUS SD eet ee

OF PANAMA

Plio.

110- 190
1235-1750
0-1660

190

140— 190
1406-1416

120

140
0-— 190
1720-1750

1236

1090-1100

110- 120
1110
0

1306— 201
0— 10

1500
180
1236

1485-1750
0

Mio-
Plio.

4540-4560

3000-5000

5290-5300

5000

5300

5300

4190-4200

5300

5290-5300

2010

4990-5000

5290

4190

5300

3230

3000-4200

57

Depth in Feet

Mio.
6250-6260

5420

5700-6390

5410-5420

5410-5420
5300
7780
6000-6350

5400
6050-6060
5420
5290
5430-5440

6350
5410-5420
5460

5430

58 CALIFORNIA ACADEMY OF SCIENCES

Plectofrondicularia californica
Cushman and Stewart
LET ROS DO GNIS SVS oer se A
POVSTOMEN OCHS DOIN e pe
PYTLO OIC ACDTESSOAOLOLDIST ype
Quinqueloculina akneriana d’Orbigny
Quinqueloculina oblonga Montagu
Quinqueloculina seminuda Reuss ............-..-
OU GILElOCU TOES De eee ee
Robulus americanus var. grandis
Cushman

Robolus cushmani Galloway and Wisslev....
ROOMS Cha Stmplec ac Orpieinyy) eee
TC OUUUES SS) ern een, ee BIO Ee). ee aeons
Rotalia subtenera
Galloway and Wissler
Sigmoilinastenus Czzek Se
Textularia abbreviata d’Orbigny ..................
Tertulamia Sp) zeae ss ee ee
Uvigerina brunnensis Karrer
Uvigerina cl nispida-costata =.
Tvigerina cf. mexicana Nuttall
Uvigerina peregrina Cushman
Uvigerina striata Schwager .........-....-..---------
Uvigerina striata cf. attenuata
Corvyellvand eMoOssmane ss eee es
Uvigerina cf. tenwistriata Reuss .............--.--
Uvigerinella cf. californica Cushman
Unigeninetiasoogsan@Cushmanis ee
Valvulineria inflata d’Orbigny
Valvulineria sp. (large)
Valwulineria sp. (small)
Virgulina bramlettei
Galloway. and Morreyo-= ee
Virgulina cf. californiensis Cushman
Virgulina floridana Cushman
Virgulina cf. nodosa
Reh pandske CStewartes eee
VAR G ALLL IVORY ST) hye es eee see eee

Plio.

1650-1660
1720
110

0-1416
180-— 190

Mio-
Plio.

4540.

5300

1900-1910

3000-3010

5290

4010-4020
2000-3010

3000-3010

5300

5000
5420-5430

5290-5300

[Oc. PAPERS

Depth in Feet

Mio.

7730
6850-6860

6340-6350

6050-6060

5420

5410-5420

5410-5420

6340-6350
6000-6060
7090-7100
6050-6060

7720-7730
6850-6860

6340-6350

The Chareo Azul is predominantly shale and siltstone, carrying
plant remains and lignitic seams as well as an abundant marine fauna
of mollusks and foraminifera. The mollusks have been described by
Olsson (1942) and the foraminifera by Coryell and Mossman (1942).
Occasional beds are sandy or limy, but there is little true sandstone
or limestone. The base is conglomeratic, and at the eastern side of

No. 23] TERRY: GEOLOGY OF PANAMA 59

the Burica Peninsula (near Puerto Armuelles) in Rio Corotti the
basal conglomerate runs to 600 feet in thickness, the boulders of the
conglomerate being almost entirely of basic igneous rocks. The con-
elomerate thins westward and is thinnest where it lies on the basal
complex near the west side of the peninsula.

The Chareco Azul is a strongly transgressive formation, its base
lying on successively older formations from northeast to southwest,
and represents an advance of the sea toward the southwest on a land
body of unknown size, which was certainly a large island and may have
been of subcontinental dimensions, since the western limit of conti-
nental structure in the eastern Pacific is a line running from a point
west of Easter Island to southern Mexico (Gutenberg and Richter
(1949), p. 27). The Chareo Azul has never been identified on the
mainland of Chiriqui Province, but may exist in a narrow belt along
the coast under alluvial cover or on the islands. It would appear that
the invasion of the sea took place northeast to southwest, suggesting
that the sea advanced over a fault block which was sinking more
rapidly on the northeast side. This agrees with present structure of
the Burica Peninsula, which consists of a series of fault blocks tilted
toward the northeast, and it indicates that such structures may exist
far to the southwest beneath the sea (fig. 6).

The Corotti well encountered no conglomerates other than the basal
conglomerate; but other conglomerates are found in the interior of
the peninsula, especially to the northwest along the strike. Since the
section is repeated by faulting, it is probable that some of these oceur-
rences are merely repetitions. Nevertheless the section appears thicker
to the northwest and the portion between the Eocene limestone and
the first conglomerate above the basal one has been differentiated on
the map (pl. I, and fig. 6) as middle Miocene and giving the tentative
name of the La Vaca formation. It is believed to be the equivalent
of the part of the Chareo Azul below 5,400 feet in Brixey’s division,
where the middle Miocene would have only member status.

In the Corott well, 7,785 feet of sediments was encountered. The
field work indicated that about 1,100 feet of the formation had been
removed by erosion at the well site, making a total of 8,885 feet, a
figure reduced by the fact that the dipmeter readings indicated dips
of 8° to 20° at various points in the hole. Allowing for this reduc-
tion, the total thickness of the formation would be between 8,000 and
8,500 feet, probably nearer the latter. Of this thickness about 2,700
feet would be undisputed Pliocene, 3,500 feet Mio-Pliocene, and 2,300
feet undisputed Miocene. All paleontologists who have worked on the
Chareo Azul fauna have noted the moderately deep to deep-water

60 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

character of the fossils. This is also borne out by the lack of coarse
sediments, except at the base.

On the Caribbean side, the Pliocene is represented by a group of
coarse sandstones and soft shales near Puerto Limon, Costa Rica,
from which Gabb (1881) described a molluscan fauna; and by the
boulder conglomerates of the Talamanea valley and adjacent regions
in Bocas del Toro and Costa Rica. Olsson (1922) has noted the pres-
ence of interbedded thin blue clays among these conglomerates, carry-
ing a small fresh-water fauna. On the northwest coast of Columbus
Island, Bocas del Toro, Pliocene coral-reef limestones with inter-
bedded bands of marly shale have been found in small outcrops
[Olsson (1922) ].

PLEISTOCENE

The Pleistocene of central Panama, identified only in the Canal
Zone, consists of muds along the coast east of Colon and in Limon
Bay; it is also found in borings in the northern part of the Canal Zone.
They are littoral and swamp deposits. They have been described by
MacDonald (1919), Woodring and Thompson (1949), and Jones
(1950).

Pleistocene has not been recognized in eastern Panama, although
no doubt present over large areas. In western Panama a group of
soft clays with layers of sand, outcrops in Rio Rabo de Puerco and
Monte Verde ravine near Puerto Armuelles. In Rabo de Puerco a
conglomerate forms the base of the formation. The total thickness
is unknown, but apparently exceeds 600 feet. The upper part of the
formation lies offshore or beneath the alluvium to the east. The base of
the formation is found inland up to elevations of 100 feet or more above
sea level. From these beds Olsson (1942) has identified 113 species.

RECENT

Recent deposits consist of stream deposits or outwash from vol-
canic elastics or other unconsolidated rocks. For the most part they
occur on the flood plains of streams or along the coast or in swampy
areas or pocket valleys such as the Talamanca Valley, close to steep
mountain slopes. In such localities they often form boulder and
gravel fans, but in general they are sands, silts, or muds, and are
flat or with gentle slopes.

STRUCTURE

Central America from Salvador to northern Costa Rica, including
eastern Honduras, Nicaragua, and northern Costa Rica, is here con-

pography = Caribbean Region
AMERICAS. by The American Geographical
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No. 23] TERRY: GHOLOGY OF PANAMA 61

sidered to form the western end of the Caribbean are, of which the
other visible features are the Greater Antilles and Lesser Antilles,
which are separated from northern South America by the Caribbean
basin, an arcuate submarine depression with a maximum depth of
something over 5,000 fathoms. The Caribbean arc is considered by many
ceologists and geophysicists to be a typical representative of the Pacifie
island ares, the features of which have been set forth by Gutenberg
and Richter (1949), as follows:

Beginning on the convex side of the are

A—An oceanic trench.

B—A narrow belt of shallow earthquakes and negative gravity anoma-
lies, on the concave side of the trench. This belt frequently rises
in a ridge, which may emerge into small nonvolcanic islands.

C—A belt of maximum pesitive gravity anomalies, with earthquakes,
frequently large, at depths near 60 km.

D—tThe principal structural are of late Cretaceous or Tertiary age with
active or recently extinct volcanoes. Shocks at depths of the
order of 100 km. Gravity anomalies decreasing.

E—A second structural are. Vulcanism older and usually in a late
stage. Shocks at depths of 200-300 km.

F—A belt of shocks at depths of 300-700 km.

Details vary widely from region to region; often one or more features
are poorly represented or unknown.

When these features are combined in a diagrammatic section, they
suggest that a typical island are is underlain by a sloping fault plane
or zone of fault planes which emerges at the oceanic trench and dips
toward the coneave side of the are. The mechanism has been described
by Benioff (1949), the activating agent being the dense oceanic block
underthrusting the lighter continental block. The Caribbean are at
its northern front presents the trench, the belt of negative anomalies,
the shallow shocks, and a belt of maximum positive anomalies, but
no active voleanoes. At its eastern end, the Lesser Antilles, it presents
a trench (not deep), a belt of negative anomalies, and a belt of active
voleanoes. At its western end, Central America, is a trench (depth,
4,000 fathoms), a belt of shallow shocks, a belt of active voleanoes, and
a belt of intermediate shocks. The typical gravity anomalies may ex-
ist, but are unknown. These conditions extend from Salvador to
northern Costa Rica, but in southern Costa Rica and Panama there are
new and confusing factors.

There are no active voleanoes in Panama, although there was vol-
canie activity from the Eocene to the Pleistocene. Gravity anomalies
have not been recorded. The convexity of the structural and topo-
eraphie forms is mainly toward the Caribbean are, rather than away

62 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

from it, as at other points in its perimeter; but there is evidence of
local convexity to the southwest. The ends of the northeastwardly
convex ares appear to extend to the southwest as submarine swells
across the floor of the Pacific into a region described by Gutenberg and
Richter (1949) as of continental structure, although at present sub-
merged. The northeastwardly convex ares are cut by a series of radial
arcuate faults convex to the west. When these faults are projected
north and northeast across the Caribbean basin they appear to border
topographic swells and troughs. With these facts in mind, we may
take up the consideration of local structure.

EASTERN PANAMA

Central and eastern Panama show a series of concentric structural
ares, convex to the north, cut by a series of trans-isthmian faults which
intersect the concentric structures radially (fig. 4). The northernmost
of these structural ares forms the continental divide from the Colom-
bian boundary to a point a few miles east of the Canal Zone. The
core of the divide is the basement complex. Over much of its length,
its outer (northeast) flank lies in the territory of the Cuna Indians,
whose attitude toward strangers prevents geologic field work in their
territory except under military protection. In 1870, the Selfridge
expedition crossed from Caledonia Bay to the Chucunaque River,
under such protection, and the mineralogist of the expedition, Carson
(1874), reported sandstone on the outer (northeastern) flank of the
ridge. In 1947, geologists in the service of the War Department
crossed on the same route, and while no report has been published
of their work, the writer has been informed that Carson’s observation
was verified. The writer has flown over this stretch of coast several
times, he has walked across the Isthmus from Chepo to the Gulf of
San Blas, and he has studied the air photographs. Over considerable
stretches, the continental divide is paralleled on the outer (northeast)
side by a series of low ridges, such as would be formed by tilted sedi-
mentary strata. On the southwestern side of the divide the sedimen-
tary rocks dip away from the divide at fairly low angles. The
impression gained by the writer is that the continental divide is an
asymmetric anticline with the steep side toward the Caribbean. About
halfway between Nombre Dios and Punta San Blas, on the Caribbean
coast, coarse sandstones of unknown age stand on edge striking E—-W.
—Schuchert (1935).

From the head of the Gulf of San Blas westward, the rocks on the
north side of the divide belong to the basement complex, until the
Madden basin is reached, where the divide is seen to be the escarp-
ment forming the south limit of the Madden graben. The fact that

GEOLOGY OF PANAMA

.
.

TERRY

No. 23]

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64 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

the divide is here paralleled by a fault on the north side suggests
that it may be so paralleled for much more of its length.

The continental divide east of Chepo is paralleled to the south by
another igneous ridge which forms the divide between the Bayano
River basin and the Pacific. The rocks on the south side of the latter
ridge are Oligocene shales dipping southwest at low angles toward
the Pacific, where seen by the writer on Rio Pasiga and Rio Chiman.
The rocks of the northeast side are also sediments, but their attitude
is unknown. The ridge appears to be anticlinal.

In central Darien Province, the structural situation is quite differ-
ent. In the area west of the structural trough occupied by the Tuira
and Chucunaque rivers, is a group of tightly folded asymmetric anti-
clines, with their steep sides facing west and in several eases bordered
by thrust faults dipping east. Of this group, the largest is the Pirri
anticline, which separates the basin of the upper Tuira from the basin
of the Balsa. The core of the anticline is the basement complex, from
which the sediments dip to the southeast at low angles on the east
side; they stand on edge on the west side, which is cut off by a thrust
fault, striking about N. 25° E. (F. 9, fig. 4). The angle of dip of the
thrust fault is apparently high (structure section A—A).

North of this and west of the Chucunaque River lies a conspicuous
ridge, which is also the core of an asymmetric fold, the Sanson anti-
cline, which consists of vertical Oligocene and Eocene strata on the
west flank and the same formations plus the Miocene on the east flank,
dipping east at angles of 5° to 45°. The fold is cut off at its western
foot by a thrust fault striking N. 25° W., and a drag fold on its
eastern flank is cut off by a parallel fault (structure section B-B).
From the Sanson anticline to the estuary of the Rio Sabana only
some very sketchy reconnaissance notes are available. The rocks are
apparently Oligocene and Eocene, tightly folded and faulted and
standing at steep angles mostly from 60° to 90°. The outerops are
separated by swampy areas, as the entire region has been deeply
eroded, much of it based leveled. It appears that the outcrops repre-
sent portions of tight asymmetric folds, striking N. 25° W., pushed
toward the west. The air view and air photographs support this
impression. ,

Crossing the Rio Sabana and ascending its tributary from the
west, Quebrada Los Nunos, the Aquaqua black shale (early Miocene)
appears standing on edge or dipping steeply to the west near the Sa-
bana, followed by vertical Oligocene and Eocene strata with a variety

Figure 5. Structure sections. See figure 4 for the location of these sec-

tions. See plates I, II, and III for an explanation of the symbols used to rep-
resent the formations shown here.

No. 23] TERRY: GEOLOGY OF PANAMA 65

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66 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

of strikes of which N. 25° W. to N. 30° W. are the most common. Some-
thing over 4,800 feet of Oligocene and Eocene limestones and shales
with interbedded voleanics is exposed before reaching the crest of
the divide between Rio Sabana and Rio Cucunati drainage. Here the
strata flatten out and on the west side dip at low angles toward the
Cucunati. On the west side of the Cucunati valley this low-dipping
westward inclined Eocene is cut off by a cliff of basement andesite.
The contact is apparently a thrust fault (F. 8), or series of thrust
faults dipping west at a high angle (structure section C-C), (F. 8,
fig. 4). The section between the Sanson and the Cucunati is one of
the mostly tightly compressed and intricately faulted areas between
Lake Nicaragua and the Atrato River, fronted on each side by an
advancing overthrust and broken into a mass of squeeze blocks which
would be almost impossible to map in detail. The soft Oligo-Miocene
shales are so incompetent that a section 3,000 to 4,000 feet thick may
be squeezed down to 1,000 to 2,000 feet and the fault breccia of the
competent limestones, cherts, and tuffs crowded into this from each
side. Much of the area has been baseleveled by erosion, and is now
a swamp barely above the level of high tide. In these portions, the
structure is, of course, unknown. However, the Cucunati fault zone
ean be traced across the Isthmus. The writer has visited it as far
north as the head of the Rio Sabana where the soft brown Gatun
sandstones stand on edge striking N. 25° EK. The fault zone crosses the
Chucunaque in the “forbidden land” of the Cuna Indians, but from
the air a conspicuous bulge of the mountains of the continental divide
can be seen crowding southwest and narrowing the sedimentary valley
of the Chucunaque by several miles. In spite of this narrowing and
crowding, no conspicuous ridge marks the divide between the heads
of the Artigarti (Chucunaque drainage) and the Cafiasas (Bayano
drainage). The writer has flown repeatedly over this area in a small
airplane at an altitude of 800-900 feet, and neither he nor the pilot of
the plane could detect the divide between Bayano and Chucunaque
drainages. The region has been peneplaned and both streams are mean-
dering in such an intricately interlaced pattern*that in many places
it was hard to tell whether the drainage was to the north or south.
This peneplanation must have taken place after the fault movement
had ceased, indicating that the stresses which caused the faulting had
ceased before the end of Pleistocene time, and probably considerably
earlier.

Figure 6. Structure sections (continued). See figure 4 for the location of
these sections. Structure sections H!1-H and H—-H should be joined to form the
complete cross section; Cafiazas is on the Caribbean half; Rio Negro is on the

Pacific half. See plates I, II, and III for an explanation of the symbols used
to represent the formations shown here.

No. 23] TERRY: GEOLOGY OF PANAMA

Canazas

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68 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

The southern part of the Cucunati fault zone appears to pass
through San Miguel Bay and across the ‘continental shelf, and from
the edge of the continental shelf to turn south into the head of the
2,000-fathom trench which parallels the coast of northwestern Colom-
bia and Ecuador. The curve of Garachiné Point from northwest to
northeast suggests that there has been a strike slip along the fault, the
east side moving south, and the west side to the north. This strike
slip, however, is only part of the movement. The overthrust from
the northwest, or underthrust from the southeast, was evidently the
first and major movement, and the present arrangement of the out-
crops is the net result of repeated movements, not all in the same
direction.

The parallel Pirri fault (F. 9, fig. 4), 45 miles to the east, also shows
some indication of a strike slip, the east side moving south as in the
Cucunati fault. It is possible that this apparent strike slip may be
actually a secondary effect of the thrust. The Pirri fault is traceable
into the Gatun outcrop at the point where it crosses Rio Tuira about a
mile east of Real, but is less evident in the Puero and still less in the
Chucunaque, indicating that its main movement took place in Gatum
time.

West of the Pirri anticline the valley of the Rio Balsa is filled in
its lower half by alluvium over folded Tertiary sediments, mostly
Eocene. The upper half of the valley is occupied by igneous rocks of
the basement complex. West of the Balsa valley, an area of basement
rocks separates it from the Sambt valley. These basement rocks con-
tain small infaulted areas of Eocene limestone. At the west edge of
this block, the basement rocks are terminated by a fault striking
N. 30° W., forming the east side of the Sambi valley, which is filled
with Tertiary sediments dipping east at low angles, and between this
sedimentary area and the sea is another area of basement complex,
terminated at the coast by another fault. At intervals along the coast
Oligocene-Miocene shales appear, standing on edge (structure sec-
tion A-A).

The structure of Darien south of San Miguel Bay and west of the
Tuira, thus appears as a series of three fault blocks tilted toward the
east and cut off on their western edges by faults. One of these blocks,
the Pirri block, is known to be an asymmetric anticline with its west-
ern flank vertical or overturned. It is believed that the two blocks
west of it are of the same type more deeply eroded, and that the faults
which eut them off at their western edges are steep angle thrusts dip-
ping east. It is believed, also that these faults are splinter faults
from the Cucunati fault zone.

No. 23] TERRY: GEOLOGY OF PANAMA 69

The continental divide is believed to be an asymmetric anticline
with the steep side toward the east. The fact that it is apparently off-
set where intersected by the transisthmian faults indicates that there
has been movement on these faults since the anticline was formed.
However, late Miocene sediments are not much affected by these faults.

An interesting structural feature of eastern Darien is a series of
small anticlinal noses in echelon along the east side of the Chucunaque-
Tuira basin. They extend in a NE.-SW. direction and are slightly
arcuate, convex toward the southeast. On the opposite side of the
basin, a similar anticlinal nose branches from the Sanson anticline
on a NE.-SW. strike. Farther south, a drag fold rising on the eastern
flank of the Pirri anticline near the village of Aruza, strikes first north
and then northwest, crossing the Tuira River about a mile east of
the village of Pinogana and continuing across the basin on a N. 65° E.
strike.

Darien displays little seismie activity. Gutenberg and Richter
(1949) list only four epicenters, one of which (9° N.-78° W.) les near
the Cucunati fault near the Caribbean coast. This shock is described
by Kirkpatrick (1939) as the ‘most pronounced shock of instrument
record at Balboa. It was felt generally throughout the Republic.”
Gutenberg and Richter list it as of intermediate depth and of magni-
tude 7.2. Another heavy shock, of which there is apparently no instru-
ment record, took place on September 7, 1882, in which the Cathedral
in Panama City, and several other buildings suffered some injury.
Part of the old municipal building fell and the Panama railroad sut-
fered some damage. This shock is believed to have originated off the
San Blas coast, as Mr. Fred McKim (1947) was told in 1936 by one
of the oldest Indians that in his boyhood a great wave swept over the
island on which he lived, destroying all the houses and causing some
loss of life. This is the only record of a tsunami east of the Canal
Zone, and is believed to indicate a movement of the sea bottom in or
near the Gulf of San Blas.

CENTRAL PANAMA

The next important transisthmian fault zone is in and adjacent to
the Canal Zone; it is probably the fundamental reason the canal is
where it is. There are apparently several of these transisthmian faults
in a belt crossing the isthmus and emerging between Nombre Dios and
Rio Indio on the Caribbean side and between Old Panama and San
Carlos on the Pacific side. They are in some eases arcuate, convex to
the west, and vary in strike from N. 20° E. to N. 30° W., crossing the
continental divide in most cases on a nearly N.S. strike. The divide

70 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

itself in this region is almost entirely in extrusive igneous rock in
which structure is difficult to detect. The rocks are believed to be
mostly Oligocene and Miocene; and are bordered on the north by late
Oligocene and Miocene sediments dipping north in the region west
of the Canal. On the Pacifie side clastic voleanies of probable Miocene
age dip toward the sea, where dip can be seen. Gravity determina-
tions by Wuenschel, reported by Jones (1950) showed the highest posi-
tive anomalies on the basement complex east of the Zone, and increas-
ingly negative anomalies westward as far as Chorrera, which Jones
interprets to mean that these areas are underlain by lighter Tertiary
rocks, and that “the Tertiary cover over the Pre-Tertiary basement is
thicker toward Chorrera. The isogals strike E.-W.” Jones also indi-
cates the Chorrera basalt is of uppermost lower Miocene age, implying
that the thickening of the Tertiary section must be in the lower Mio-
cene, Oligocene, or Eocene. The continental divide is about seven miles
north of Chorrera and runs N. 70° E., so that the H.-W. isogals are
nearly parallel to it. This would indicate that the divide is anticlinal,
with the sediments thickening seaward on the Pacific side, as well as
on the Atlantie.

The Caribbean ends of several of the transisthmian faults are indi-
eated on Jones’ map (1950), the principal one passing through Limon
Bay, along the west shore of Gatun Lake for about eight miles, crossing
the lake and entering Trinidad River south of the lake. It apparently
controls the course of the Trinidad to the continental divide following
an arcuate course, convex to the west. Immediately east of it, the con-
tinental divide parallels it in a general N.-S. direction for some fifteen
miles, almost at right angles to its normal N. 70° E. course. It seems
unlikely that this 15-mile right-angle shift of the continental divide
resulted from strike slip along the fault, but, the faulting undoubtedly
controls its location. South of the divide the fault enters the granite
of the Campana area, which is cut by three deep parallel valleys
(beautifully shown on the air photographs), one of which leads di-
rectly up to the notch at the head of Rio Trinidad, and is undoubtedly
due to the continuation of the fault on a S. 30° E. strike, which carries
it out to sea just west of Chame. A continuation of the strike across
the continental shelf leads directly to the notch in the edge of the
shelf south and west of the Pearl Islands, and to the head of the
trench paralleling the coast of northwestern Colombia.

An interesting fault valley (F. 6) parallel to that just described
is occupied by the Boqueron River north of Madden Lake. It is in
fact a narrow graben striking N. 20° E. across the basement complex,
and is of particular interest because it contains the only manganese

No. 23] ; THRRY: GHOLOGY OF PANAMA (es

deposit in Panama which has been worked at a profit. This deposit
has been described by Sears (1919), who says it occurs in a sedimen-
tary complex of shales, sandstones, and limestones, which he does not
identify as to age, but says they are older than the sediments out-
cropping downstream, which are late Eocene. They occur in the
valley of the Rio Diablo, the tributary of the Boqueron nearest its
head. The sediments show such a confusion of dips and strikes that
Sears was unable to determine their sequence. The faults bordering
this graben can be seen in the Eocene limestone and basement com-
plex at the head of Madden Lake.

Other NE.-SW. faults can be seen in the Madden Lake basin and a
very prominent set of parallel faults striking N. 70° ES. 70° W.
intersect them, outlining opposite sides of the depressed fault block
occupied by Madden Lake. This last set of faults is very persistent.
They apparently extend eastward to the Caribbean, where they out-
line the Gulf of San Blas, and Jones (1950) shows some of them
extending west to the edge of his map, south of the middle of Gatun
Lake. Some of them extend across the Rio Indio coal fields as shown
in the figure, where they intersect a group of N.-S. faults. The regional
dip is of the order of 10° or less, but where the coal is intersected by
the faults, the dips are from 40° to 60°. A dike on one of the N.-S.
faults is intersected by two of the N. 70° E. faults, and the ends of
the dike twisted east at the south end and west at the north end.
Strike slip is shown by these ends of the dike and by the correspond-
ing shifts of the coal bed. The indicated movement is left lateral. In
the Boqueron manganese deposit the only dip recorded by Sears (1919)
is one in which the limestone is standing on edge striking N. 70° E.,
obviously on one of the series of N. 70° E. faults.

Still farther west, the N. 70° E. series of faults reappear along
the north flank of the continental divide, where they are shown in
the structure section by Hershey (1901) (reproduced with slight modi-
fications in structure section H-H). At the heads of Rio San Pablo,
Rio Cobre, and Rio Tabasara, a series of parallel arcuate valleys con-
vex to the northwest apparently mark the position of a series of splin-
ter faults along the northwestern edge of the central Panama arcuate
structural system.

The group of arcuate faults along the upper Tabasara, Cobre, and
San Pablo rivers and their branches has attracted some attention as
the locus of copper prospecting in Panama. The copper occurs as low-
gerade sulphide ores carrying gold (Riddell (1927) ).

The continental divide in central Panama west of the head of Rio
Indio follows close to the north rim of El] Valle voleano, and its south

72 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

flank for some miles is concealed by the ejecta from that crater.
About 20 miles to the west, near the village of La Pintada, andesite
flows dipping to the northwest are overlain to the south by rhyolite
flows and tuffs dipping south at a low angle. The northwest dip of
the andesites can be seen along the edge of the hills bordering the
west edge of the plain which extends from Penonomé southward to
the coast. The Pan-American Highway from Penonomé to Nata fol-
lows a course approximately parallel to and a little southeast of an
arcuate anticlinal axis, on the northwest side of which the andesite
flows dip to the northwest, while on the southeast side the rhyolite
flows dip to the southeast. This axis appears to be the continuation
of the anticlinal axis which forms the continental divide east of La
Pintada. It can no longer be followed after entering the coastal plain
a few miles north of Aguadulee, but on crossing the plain in a south-
westerly direction it can be picked up again. At Pesé, Oligocene eal-
eareous shales dip northeast, while about seven miles to the west near
Oct they lie nearly flat apparently on the anticlinal axis, and farther
west near the head of Montijo Bay they dip northwest. South of Pesé
in the vicinity of Macaracas, the dip of the Oligocene and Miocene
changes from northeast to east and to southeast as one goes south
(Joukowsky and Clere (1906) ). It appears that an anticlinal axis run-

Fault Pattern
Rio Indio Coalfield

S
$
2
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faullie == =
Strike- Slip —+

Coal Qufcrop 4,
Dip and Strike of coal Bs

Figure 7. Fault pattern—Rio Indio coalfield.

No. 23] TERRY: GEOLOGY OF PANAMA 73

ning NE.-SW. through Oct continues southwest to the coast at some
point east of Punta Mariato and west of Morro Puercos. The greater
part of this region is basement complex bordered on the west by a
narrow band of Eocene and Oligocene sediments along the east shore
of Montijo Bay, and on the east by the Eocene and Oligocene of the
Tonosi valley. The Tertiary sediments curve round the nose of the
igneous northeast of Oet, and near Las Tablas can be seen to dip
underneath another band of andesite flows which border the east coast
of the Azuero Peninsula. These andesites are believed to be a part of
the same group of flows as those which appear west of the road from
Penonomé to Nata.

Whether the anticlinal axis described above was originally con-
tinuous with the one extending southwest from La Pintada is not
known. At any rate they are separated by a transisthmian fault (F. 4,
fig. 4) striking N. 42° W., which ean be clearly seen from the air or on
the air photographs, although difficult to trace on the ground as it
traverses a low flat region of swamps and coastal plain from Agua-
dulce south. To the north it cuts across the isthmus in a region entirely
igneous. Its course to the south can be located by a succession of dikes,
shifted stream courses, and small linear depressions, on the eastern
coast of the Azuero Peninsula; and where its extension crosses the
edge of the continental shelf, it is marked by a deep reentrant as far
as the 1,000-fathom isobath, but ean not be traced farther. Whether
this fault belongs to the same system as the arcuate transisthmian
faults farther east is not apparent.

The anticlinal, described above, which occupies the west side of
the Azuero Peninsula is cut by a great number of faults, only a few of
which are shown on the map. The commonest strikes are from N. 25°
W. to N. 55° W., but there also are numerous others on various
strikes. The writer is indebted to Dr. E. R. Dunn of Haverford Col-
lege for the following notes on a region on which there is practically
no other information. His letter reads:

I have had my rocks determined at the Bryn Mawr Geological laboratory,
and this is about what I have to report.

We went pretty nearly straight south along Oct, Las Minas, and thence
south along the divide. At first this was pretty straight and we didn’t have
to cross much water, but later it began to swing very widely.

1. At Octii sedimentary rocks were exposed, lying almost horizontally.
The terrain is pretty flat and it is savanna country. Altitude 300.

2. We got into hills before we reached the Parita River. At the river
sedimentaries were exposed, lying nearly vertically with an E.-W. strike.
Altitude about 300.

3. Around Las Minas we saw quite a bit of manganese ore and of course

74 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

there was a gold mine there once, with pretty old workings but I imagine
there is plenty of dope on that.

4. Rock was exposed in the bed of the Quebrada Piedra, some 20 miles
south of Las Minas. This stream was said by Davies to enter the La Villa
(the river which forms the border between Herrera and Los Santos). This
was andesite at an altitude of about 1,500.

5. North face of Mangillo partial section. Altitude about 2,500 to 3,000.
Bottom (Davies saw this, I didn’t), sedimentaries dip 50° W., strike N-.-S.,
then andesite (I saw this and have a piece), on top of the andesite sedimen-
taries, limestones and shale, dip 30° S., strike E.-W. (I have some of this).
This was exposed in the bed of a small stream running north to Queb.
Piedra. There is no doubt of the sedimentaries on top of the andesite. Ex-
posed on the top of Mangillo was some andesite, thus andesite both above
(since the top was south of the stream exposure) and below the sedimentaries
I saw, and if Davies is right, and I see no reason why not, you have from
bottom up, andesite, sedimentary strike N.-S., andesite, sedimentary strike
E.-W., andesite.

6. Going south from Mangillo, on side of a long ridge, at head of a small
stream, rhyolite was exposed at about 2,000. Stream tributary to Rio Quebro.

7. At Dos Bocas, 375 feet where the Quebro really starts as a combina-
tion of a big stream coming from the west and another coming from the east
(the one from the west rises on Cerro Negrito and is mapped as running
west) there were many granite boulders in both branches, obviously coming
from somewhere upstream. Alluvial gold was present.

8. The exposed rock at this place, forming the walls of the canyon, was a
smooth green serpentine.

From Las Minas south, we crossed east-west ridges in the following order:
Penalosa, Buenavista, Jacinto, Piedra de Tigre, Macaracito, Mangillo. We had
to cross the head of a small west-flowing stream (tributary to Negro-Mariato)
to reach Macaracito, which ridge was said to run down to Macaracas. We
had to go down pretty far and cross a larger east-flowing stream (tributary to
Lavilla) to get to Mangillo. Beyond Mangillo we had to go down to 375 feet
and hit the canyon of the west-flowing Quebro.

From the situation at the Parita, and on the north slope of Mangillo, it
looks to me that these ridges are structural and based on titled (folded ?)
sedimentaries, interspersed with volcanics and based on intrusives.

Davies says that the serpentine at Dos Bocas (which he called dunite) is
exposed in Cerro Negritos near the west coast.

At any rate, there are tilted sedimentaries in the very middle of the penin-
sula at 2,500 feet.

The rock exposed on top of Cacaranao, 3,300, looked like the rock on top
of Mangillo (andesite).

Dunn’s notes on serpentine and dunite are of particular interest,
in view of Hess’s theory of the relation between serpentinized basic
rocks and the course of old island ares.

The eastern half of the Azuero Peninsula is also occupied by an
anticlinal axis, arcuate and convex to the northwest. In the axial region,

No. 23] TERRY: GEOLOGY OF PANAMA 75

granite is exposed, with heavy basic igneous rocks to the east. It is
bordered on the west by the Tonosi valley Eocene which is connected
with the Tertiaries to the north by a narrow corridor of Oligocene and
Miocene in the region of Macaraeas. This sedimentary band is over-
lapped in the southeast by voleanies partly from Cerro Quema, which
MacDonald (1937) considers a Pleistocene voleano.

The continental divide west of La Pintada is not anticlinal, but
apparently consists of a series of fault slices striking NW.-SE. cutting
the andesite flows and dikes at the top of the Oligocene-Miocene se-
quence which farther southwest is interbedded with sediments of that
age. The orientation of stream courses is interesting. The rocks on
both sides of the divide are igneous, those on the north being granite,
syenite, and andesite in the region of Mineral and to the west, and
on the south side the andesite flows mentioned above. Seen from the
air, the north side is a series of precipitous ridges, separated by deep
narrow canyons, which instead of running straight to the sea as might
be expected in a region of igneous rocks of great relief close to the
sea, form a parallel series at an acute angle to the sea on a strike of
about N. 45° W. They appear to be caused by parallel faulting.
South of the divide the streams run in courses S. 70° W. parallel to
the divide and gradually curve more to the south in their lower part.
Some sharp changes in the course of the divide are probably due to
faulting. However, the region has not been studied, and although
there has been a good deal of mining going on ever since the Spanish
conquest, there are few references in the literature to regional struc-
tur, aside from Hershey (1901) and Wagner (1862). Taylor (1852),
however, indicates that the rocks show stratification, and refers to
“pyorphyroid, pyritous, ferruginous, granitoid trap,” and on his map
shows the contact of porphyry and trap running about N. 85° E. near
the mouth of Rio Escribanos near Belen, and shows the strike of the
gold-bearing quartz veins as parallel to it, suggesting that there may
be a fault system causing the structure. In view of the fact that
granite and syenite, mentioned by Wagner (1862) and Hershey (1901)
in the coastal region near Mineral, are considered by all the geologists
with the exception of Gabb (1875), to belong to a pre-upper Eocene
complex, the map (pl. II) represents this area as basement complex.

The Azuero Peninsula is second only to southwestern Chiriqui as a
locus of seismic activity. The greatest and most destructive activity
took place in 1913, and was investigated by MacDonald (1913), whose
account was published in the Canal Record of December 10, of that
year. The epicenters shown on the map are based on MacDonald’s
work. The fault along the east coast of the Azuero Peninsula is ap-

76 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

parently the cause of many small shocks recorded on the Balboa
seismograph.

The arcuate form of the major structural features of central and
eastern Panama resembles that of a typical island are of the Pacific
type, and the occurrence of serpentine and dunite on its outer flank
in Veraguas conforms to Hess’s theory of the association of such rocks
with belts of negative gravity anomalies in the island ares of the East
and West Indies. However, nothing is known as to the distribution of
oravity anomalies in Veraguas.

WESTERN PANAMA

In western Panama, as in eastern Panama, there are a series of
areuate anticlinal and synclinal folds. They are convex to the north-
east, for the most part, but voleanic ejecta of Pliocene and Pleistocene
age in enormous amount have concealed the structure of the Tertiary
sediments over much of the area. Voleanics of contemporary origin
are also interbedded in the Oligocene and Miocene sediments, but per-
haps to a lesser degree than in central Panama. The two arcuate struc-
tural systems of eastern and western Panama are separated by a fault
(F. 3, fig. 4), running N. 24° W. from Montijo Bay to the Valiente
Peninsula, and other faults on the same strike occur to the west of it.
The writer crossed this area from the head of navigation on Rio Cri-
camola to San Felix. No sedimentaries were observed north of the
divide, but they may be concealed under the alluvium of the coastal
plain which is three or four miles wide. The observed rock in place
south of the coastal plain along the Cricamola was andesite, but no
structure could be detected until the continental divide was reached
where flat-lying lava beds were observed. On the south side of the
divide, slopes of very fresh voleanic ash were crossed, the Indians who
accompanied the writer spreading out along the path to avoid start-
ing a slide. The first sediments were observed about seven miles south
of the divide where foraminiferal shales of Oligocene age dipped south
at a low angle. They appeared to be interbedded with voleanics, but
all rocks seen were so deeply weathered that it was difficult to dis-
tinguish the tuffaceous shales from the tuffs. The age of the beds was
inferred from a Glyptostyla ef. panamensis collected by Olsson some
miles north of San Felix. The contact of the sediments with the
igneous is known to be a few miles east of Tolé, and to reach the sea
near the mouth of Rio Tabasara, but the region has not been mapped
in detail. The contact apparently follows an are convex to the north-
east, suggesting that it is following the curve of an anticlinal axis to
the east. The axis connects the Sona Peninsula (believed to be base-

No. 23] TERRY: GEOLOGY OF PANAMA 4

ment rocks from the presence of the bedded cherts at Bahia Honda),
with the continental divide near Cerro Santiago, and is thus, strue-
turally and petrographieally, the continuation of the continental divide
of Chiriqui and Boeas del Toro, although it is no longer the continental
divide. The southwestward trend of the isobath contours off the coast
indicates that the structure continues out to sea in that direction. The
continental divide from Cerro Santiago east is apparently a series of
fault ridges without anticlinal folding.

Folding on lines approximately parallel to the continental divide
takes place on both sides of the isthmus in western Panama, two gen-
eral zones of folding being present on each side; and there are many
faults. Most of the folds on the Caribbean side are asymmetric with
the steep side toward the sea, and in several cases are faulted on the
steep side, with a strong suggestion of thrust faulting. In one case this
suggestion was confirmed by drilling. On Columbus Island, at the
northwestern end of Chiriqui Lagoon, the surface structure was inter-
preted by geologists as a gently rounded dome on which the early
Miocene Conch Point shale outcropped at the crest, over an area per-
haps a mile in diameter, surrounded by the Bastimentos shale of
middle Miocene age. A seismograph survey indicates that the strue-
ture is cut by a fault striking N. 24° E. (F. 2, fig. 4).

The result of drilling is indicated in the following excerpt from a
report of the paleontologist, A. D. Brixey, Jr., who examined the well
cuttings:

Excellent proof of thrust faulting within the Bocas del Toro dome section
occurs between 1,630 and 2,520 feet and between 4,350 and 4,570 feet, re-
spectively. At 1,630 feet a zone of fossilized, large (2-4 mm.) flat seeds
(Seeds A) is followed by a zone of Virgulina sp. a, and a zone of Siphonodo-
saria sp. a at 2020 ft. At 2,120 Seeds A recur, followed by Virgulina sp. a
at 2,370, and another zone of Siphonodosaria sp. a at 2,520. This would indi-
cate thrusting of a section of 390 to 400 feet.

The second phase of major thrusting between 4,350 and 4,360, a sandy
facies, poor microfauna with the exception of a rather small Globigerina
bulloides followed by a zone of Amphistegina lessonii and an abundance of
Miliolidae. Again between 4,530 and 4,540 a sandy facies was noted, a poor
microfauna followed by small Globigerina bulloides and a zone of Amphi-
stegina lessonii and Miliolidae. Another zone of possible thrusting occurs be-
tween 6,360 and 6,380 feet and 6,750 to 6,780 feet where the microfauna again
show a significant repititious similarity.

In addition an unprecedented thickness of the Conch Point shale
was encountered. The measured thickness of the Useari (the inshore
equivalent of the Conch Point) rarely exceeds 5,000 feet, and was no-
where estimated at over 6,000, but the well penetrated 8,621 feet and

78 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

was abandoned because of drilling difficulties in heaving shale, with-
out reaching the base of the formation. A dipmeter reading at about
4,500 feet gave a dip of about 25° to the southwest, and cores showed
even higher dips. It seems obvious that the structure of Columbus
Island includes a series of thrust faults. If a fold is present it is asym-
metrie with the steeper side toward the Caribbean.

The largest inshore anticline mapped is Senosri Hill near Guabito
on the Sixaola River. This structure is a faulted anticline with vertical
or overturned beds on the seaward (northeast) side and dips of 40°
to 45° on the southwest side. Further inland a smaller structure, the
Yorkin anticline shows similar dips. The axis of the fold turns west-
ward up the Talamanea valley. Near Old Harbor in Costa Rica, ver-
tical and steep-angle dips occur in the Gatun formation on the coast,
and steeply dipping Oligocene shales are to be seen along the line of
the railway between Almirante and the Changuinola River in Panama.
Between the Chiriqui Lagoon and the Sixaola River the coastal plain
is five or six miles wide with no exposures of consolidated rocks, but
a couple of miles beyond the Sixaola in Costa Rica a band of Oligo-
cene, Miocene, and Pliocene rocks appears fronting the sea. The
strike gradually changes from N. 50° W. to N. 70°. W. to W., and
finally the Miocene rocks disappear under the Pliocene boulder con-
elomerate in which little or no bedding ean be detected. H.-W. strike
is also seen in the early Miocene shales which outcrop in a narrow
band along the north side of the Talamanca valley, and which also
disappear under the boulder conglomerates. There are numerous drag
folds, some of which develop locally into small anticlinal and synelinal
structures, but the regional structure is arcuate with the steeper side
facing northeastward. This convexity is reflected in the course of the
continental divide but is obscured by the cover of Pliocene and Pleisto-
cene voleanics; and similar suggestions of arcuate structure on a large
scale with minor drag folds can be seen on the Estrella, Banana, and
Blanco rivers.

These arcuate folds are cut by transverse faults, some of which
may belong to the transisthmian system of central and eastern Panama
deseribed above. Others appear to be merely stretch faults incidental
to deformation. A study of some of the “smooth sheets” on which the
charts of the Hydrographie Office are based was made by the writer
(1941). The “smooth sheets” show all the soundings instead of the
three to five per cent usually shown on Hydrographie Office charts, and
the detailed contouring of the continental shelf reveals some obvious
continuations of faults observed on land, and suggests the presence of
others so far unmapped. Some of these faults have been indicated on

No. 23] TERRY: GEOLOGY OF PANAMA 79

plates I, II, and III. Those off the mouth of the Sixaola River, Bocas
del Toro, and Valiente Point are of particular interest. The shape of
the edge of the continental shelf off Cahuita Point as shown on the
hydrographic charts is also indicative of faulting on a grand scale,
with strike slip shown along the course of the Sixaola River at the end
of Senosri ridge. Andesite dikes appear along the course of this fault
north of the Rio Sixaola.

On the south side of the continental divide, middle Miocene
(Gatun) shallow water and terrestrial sandstones with thin beds of
lignite appear both east and west of El Bart, the Volean de Chiriqui.
The ejecta of the voleano conceal the structure over an area of 600 or
700 square miles, but at the edges of the voleanics folds appear which
presumably continue beneath the cover of tuffs, agglomerates, and
flows. The visible folds of the Tertiary sediments roughly parallel
the course of the divide and bring the base of the sedimentary series
to the surface near David and near Brefon. Whether a continuous
fold connects the two is not known but they lie on approximately the
same strike. A complex fault network complicates the structure near
David. Only the principal faults are shown on plate I. The outerop
of Eocene limestone on the David River about three miles northeast
of the town is the first appearance of this formation west of Montijo
Bay. It occurs at the intersection of two faults, one striking N. 35° W.,
the other N. 78° 30’ W. The latter brings the basement rocks in contact
with the middle Miocene and is apparently the older of the two. The
other crosses the Majagua River east of the railroad bridge and for a
distance of about three miles is marked by a large andesite dike, which
furnishes road metal for the David-Boquete Highway. To the south
the fault ean be traced to the coast. Its intersection with Rio Chiriqui
is marked by a sharp hairpin bend of the river about a mile in length.
At the limestone outcrop on David River, dark shales, apparently of
early Miocene age, are standing on edge striking N. 35° W. on the
left bank of the river, while on the right bank, the limestone dips
80° N. and strikes N. 75° W. The indicated stratigraphic displace-
ment is over 3,000 feet, while on the older N. 78° W. fault, the entire
Tertiary section below the mid-Miocene is missing, showing a displace-
ment of not less than 5,500 to 6,000 feet. This fault’s course westward
is marked by a low escarpment in the Pleistocene voleanics and judg-
ing by the topography, continues west across Costa Rica to the coast,
intersecting Golfo Dulce en route. It is not apparent that this fault
is due to the stresses of the arcuate folding. There seems to have been
movement on it recently, forming a scarp in Recent gravels west of
the Chiriqui Viejo. Another fault on a strike N. 71° EH. converges

80 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

on the other two near their intersection, and this one is marked by a
much sharper escarpment near Concepcion, and by a line of small
igneous hills, apparently dikes. The two faults diverge westward and
eross the Chiriqui Viejo River about five miles apart. The interval
between them includes the erest of a rather tightly folded anticline,
with the complete Eocene section showing at the crest and on the north
flank, the complete Tertiary sedimentary section up to and including
at least a part of the middle Miocene. On the south side of the fold a
small section of Oligocene shale is exposed, which is followed to the
south by the alluvial flats occupied by the banana farms of the United
Fruit Company. The alluvial area is about 12 miles wide and beyond
it to the south are the gently arcuate folds of the Burica Peninsula,
including marine Pleistocene as well as Tertiary.

The contact of these folded sediments with the alluvium is a fault
(F. 1, fig. 4, Structural pattern) which is traceable on land and under
the sea for a distance of more than 350 miles. It probably extends
much farther. From Puerto Armuelles to and beyond Jicarilla Island,
it coincides with a submarine cliff, which off Jicarilla drops 5,400 feet
in three miles. On land its course can be plainly traced on air photo-
eraphs and ean be seen at Golfito. At El Cajon, a box eanyon on Rio
Diquis about four miles above Palmar, Costa Rica, on a fault parallel-
ing it, the basement rocks are thrust to the southwest over the Eocene
limestone. This fault plane dips 60° to the northeast, suggesting
that there is a zone of thrust faulting, of which both faults are a
part. Three recently active voleanoes of Costa Rica lie on the fault
first mentioned (F. 1, fig. 4) and a fourth is close to it. An oceanic
trench, slightly arcuate with convexity to the southwest parallels
the coast of Nicaragua and Costa Rica, and numerous earthquakes of
shallow depth (less than 60 km.) have epicenters between the trench
and the shore. On land a belt of active voleanoes and shocks of inter-
mediate depth (70 to 300 km.) parallel the trench. No gravity anoma-
lies have been measured, but the other features are characteristic of
an island are of the Pacific type, which implies the presence of a
thrust fault or zone of thrusting which dips toward the northeast.
It is believed that the long fault described above is a part of this
zone of thrust faulting, or at least is due to the same stresses. A
series of faults striking about N. 45° E. are found in Chiriqui Prov-
ince, the most important passing through Puerto Armuelles, crossing
the Burica Peninsula and making a perceptible re-entrant in the con-
tinental shelf where it enters the Pacific. These faults intersecting
those of NW.-SE. strike, break up the area into a number of fault
blocks, which are at present unstable.

No. 23] TERRY: GHOLOGY OF PANAMA 81

For the past 30 years, this general area of southwestern Panama
and southeastern Costa Rica has shown the greatest seismic activity
in the isthmian region. The climactic year was 1934, and the most
destructive shock took place on July 21 of that year at 5:00 am.
The epicenter is shown on the map as number 5. (Epicenters are lo-
cated by Gutenberg and Richter (1949) to one fourth of a degree,
leaving a margin of error of one eighth of a degree, about 814 miles.
There is reason to believe that the location given above is incorrect,
or one of a simultaneous flock.)

The Chiriqui Land Company, a subsidiary of the United Fruit
Company, suffered losses of close to a million dollars, including the de-
struction of a pier and banana-loading machinery, housing and other
structures, and fruit which rotted before new loading devices could
be installed. Unfinished houses thrown down were thrown to the
southwest. The rails of the railroad which erosses the NE.-SW.
fault at right angles were thrown into sigmoidal kinks, but were un-
broken, indicating a shortening of the surface from northwest to south-
east. Cracks opened on the beach in a NE.-SW. direction and re-
mained open several hours. No tsunami was observed at Puerto Ar-
muelles, but a small one was observed at Punta Burica. Landslips
occurred along the line of the N. 45° E. fault for a few miles to
the southwest but beyond that the region is unsurveyed virgin forest
and destruction was not recorded. The fault controls the course of
the Rio Guanabanon at several points and a confusion of steep dips
is observed in the Pliocene and late Miocene sediments at these places.
The fault zone is about 100 feet wide where it crosses the Rio Corott,
with the beds standing at 60 to 90 degrees. In 1949 a well was drilled
about 1,300 feet northwest of the fault. This well entered the fault
at 7,785 feet indicating a hade of 10° to the northwest.

On the Caribbean coast two intersecting systems of faults, one
striking NW.-SE. and one NE.-SW., are apparently the product of
the same stresses as those of the Pacific side. The edge of the conti-
nental shelf is notched at points where it is apparently intersected by
some of these faults. Seismic activity, however, is apparently less
than on the Pacifie side and damage has been comparatively small.

A summary of the structural conditions in the isthmus indicates
that in both eastern and western Panama, asymmetric anticlines fac-
ing toward the sea are found on both sides of the country. These
structures are believed to be, in most cases, cut off by offshore thrust
faults dipping toward the land. Most of the structures facing the
Caribbean are arcuate and convex to the north. Those facing the Pa-
cific are straighter but may be parts of larger arcuate folds. In

[Oc. PAPERS

CALIFORNIA ACADEMY OF SCIENCES

82

faults intersect

1an

.

f transisthm

the folds, and at some of the intersections there is indicated strike

» a Series O

eentral and eastern Panama

ement being left lateral. The transistbmian faults

strike NE.-SW. in eastern Panama, N.-S. in the region of the Canal

general mov

the

slip,

Zone, and NW.-SE. in Veraguas and Coclé. Similar transisthmian

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Areal Geology of Cana District b bye

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Areal geology of Cana District, by Dr. H. Veach.

Figure 8.

No. 23] TERRY: GEOLOGY OF PANAMA 83

faults probably occur in western Panama, but are obscured by Pleisto-
cene and Recent volcanics.

If the offshore thrust faults are projected downward they inter-
sect, giving the isthmus the appearance of a wedge uplifted by pres-
sure from both sides. These stresses have apparently arrived at an
isostatic balance in eastern Panama, are slightly active in central
Panama, and are vigorously active in western Panama. The sinuous
form of the country may be due to local variations in the pressures
from the two sides. The squeezing appears to have begun at the east
and moved westward. The elevation of the isthmian region which be-
gan at the end of early Miocene time apparently had brought all or
nearly all the region above sea level by the middle Pliocene. Wood-
ring (1949) has stated the case as follows:

According to vertebrate paleontologists familiar with the Tertiary land
mammals of North and South America, the Panama bridge was completed and
open to traffic immediately after the end of middle Pliocene time, about 5
million years ago. The first North American migrants, however, reached South
America in the late Miocene or early Pliocene, and the earliest South American
invaders reached North America in the middle Pliocene. These first arrivals

in both continents were small animals and presumably reached their destina-
tion by using still separated spans and completed piers as stepping stones.

Economic GEOLOGY

Gold mining in Panama goes back to pre-Colombian days and was
vigorously continued by the colonists. The metal is to be found in
streams heading in the cordillera of the continental divide from one
end of the country to the other, as well as in the Azuero Peninsula.
Some of the old Spanish mines have been reopened in modern times,
but the results in general have been disappointing. Mineralization
was shallow, and the Spaniards, despite their lack of modern machin-
ery and technical knowledge, were able to work everything but ores
of grades so low as to be unprofitable even now.

Panama’s most famous mine was the “Espiritu Santo,” near the
now-abandoned town of Cana in Darien Province. This mine, one of
the Spanish erown’s richest revenue producers, was worked from the
early part of the seventeenth century to 1727, about one hundred
years, when on account of the raids by buccaneers it was declared by
the viceroy to be a menace to Spanish rule in the isthmian region and
abandoned. It was rediscovered in the latter part of the nineteenth
eentury.

Woakes (1899) has given an account of the mineralization, from
which the following excerpt is taken:

’

The country rock is essentially andesite in an extremely decomposed state.

84 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

There are two predominant series of cleavage planes apparent, the first, gen-
erally the most marked, running N. 55° W. with a westerly dip, and the
second running N. 65° E. with a southerly dip. Roughly speaking, the ore-
body appears to have been formed in an irregular quadrilateral, the N. 55° W.
cleavages forming the east and west walls while the N. 65° E. form the
north and south walls. In adopting this theory, liberal allowance must be
made for the variations of bearing, such as would naturally occur in fissures
running through such brittle and jointy rock. The sides of the quadrilateral
figure are by no means equal or parallel in their entire length. The longer
side or base of the figure may be taken as that forming the north wall of
the deposit, the shortest is then the opposite or south wall. This gives to
the figure the shape of an irregular truncated cone. So far as can be seen,
the extreme length of the deposit from east to west is 120 feet while from
north to south it is about 90 feet....

By far the greater part of the ore-body is composed of boulders and rock
fragments of the adjoining country rock, varying in size from pieces as small
as a walnut to masses of many tons weight. They are generally completely
angular, but at times are as round as a pebble. In the writer’s opinion this
roundness is due not to the action of water but rather to a process of decompo-
sition. The rock fragments are completely surrounded by concentric shells of
brilliant, crystalline sulphurets and calcite. The order of deposition of these
minerals around the matrix is generally iron pyrites, then blende, and then
galena, with an outer covering of calcite, in which occur acicular quartz
crystals.... The gold occurs for the most part in a crystalline form, but often
as wires or strings. It is found adhering to the sulphurets, and no doubt the
very fine gold is disseminated through them. It is a rule that the greater the
percentage of zinc and lead sulphides, in the ore, the richer it is in gold. Three
distinct classes of ore have been observed in the lode mass. In the vicinity of
the walls, especially the north and south walls of the deposit, the cementing
materials of the breccia are chiefly calcite and quartz, while the matrix is
softer from more advanced decomposition. Here, therefore, we find low grade
ore. Immediately inside this mass, which varies from 15- to 40-feet wide at the
different levels, and reckoning from north to south, we find the interstices of
the breccia not entirely filled up with the cementing material, an infinity of
vugs being left. Here calcite, quartz, and iron pyrites, all more or less crystal-
line, form the cement. This class of ore assays from one to one and a half
ounces of gold per ton, according to the amount of matrix present. To the
center and southwest of the lode mass we find the ore very rich in the sul-
phides of zinc, lead, and iron, all more compact, the vugs being absent. This
may be said to be the best class of ore in the mine. Occasional pockets and
veins of a soft and friable mixture of all the lode-forming constituents are
met, containing free gold in quantity.

No. 23] _ TERRY: GEOLOGY OF PANAMA 85

Following a bad cave-in in 1911, the mine was abandoned, as pro-
duction had fallen to an unprofitable level. Production figures for the
years 1899 to 1907 are given as follows by Oller (1933) :

Produccion por anos en libras esterlinas (production by
years in pounds sterling) :

TEGO TOUU CHE SN ee ree eal ce et 91,671
SIO TAU eerie ty ea ean a eR 43,833
TOU Wn te ae angen te, 41,031
Tae ee Meme eee te no A 66,970
TGs uncer ce Garr naar . Lope ie ieee ane 154,418
TODS AE eee Roe eTeT ie 52,164
HOO GRES i eee nee ee. eh 50,070
LOO eee eae te One SR: 20,000

Other old Spanish mines have been reopened at Remanse and
Mineral in the province of Veraguas, where some production was at-
tained, and near Capira, in the province of Panama, but there are
now no active operations.

Mineralization in basic rock practically always is accompanied by
propylitization of the andesite. A few slides from specimens taken by
the writer near the old adit to the Cana mine were determined as
follows by Isotoff :

T 77 —Cana (country rock) Basalt. Intersertal texture-laths of labradorite,
grains of augite, etc. Interstitial glass is heavily charged with red
iron oxide dust. Phenocrysts of bytownite and augite. Chlorite, opal,
and carbonate are conspicuous.

T 78-T 79—Cana. Propylitized basalt. These sections exhibit various de-
grees of propylitization of the basalt described under T 77.

T 96 —Pio Nono mine—Darien. Country rock. Augite andesite.

T 97b—Pio Nono near vein. Propylitized augite andesite.

T 100-T 104—Sta. Lucia mine—Coclé. Propylitized augite andesite.

Manganese oxides occur in small quantity in many parts of the
country, but mining operations have been profitable only when war
preparations caused unusually high prices. The only such operation
on a commercial scale was in the upper valley of Rio Boqueron, be-
tween Madden Lake and Nombre Dios. The deposit was reported on
by Sears (1919), who regarded it as a blanket deposit formed by the
alteration of primary ore of unknown character, with subsequent ero-
sion and redeposition in sedimentary rocks which he was unable to
date. The region has been intensely faulted and the ore occurs largely
as breecia, some of the boulders being 8 to 10 feet in diameter. The
work was carried on under the stimulus of the high prices occasioned
by World War I and was abandoned after the war.

86 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

A manganese deposit of the blanket type occurs near Bahia Honda
on the southwest coast of the Sona Peninsula in Veraguas, in a region
of pre-upper Eocene igneous rocks. No reports on it are known. Man-
ganese ore also occurs in some quantity near Las Minas in the Azuero
Peninsula and in other places.

Copper has never been mined in Panama, but occurs as low-grade
sulphide deposits in the province of Veraguas south of the continental
divide on the Vigui, Cobre, and Tabasara rivers, and near the head of
Rio San Felix. Gold occurs with these copper sulphides and the oc-
currence of a gold-copper natural alloy has been reported from the
region of Remanse, but no reference to it has been found in the
literature.

Riddell (1927) reported the existence of a hematite deposit near
La Mesa, and unsuceessful attempts have been made at commercial
exploitation of magnetite sands on the Caribbean coast near Old Har-
bor, Costa Riea.

Coal and lignite beds oceur at many places in Panama and Costa
Rica. They appear in beds of middle Miocene age in the islands and
shores of the Chiriqui Lagoon in Boeas del Toro Province and on the
upper Changuinola River in the same province, and continue north-
ward in Costa Rica as far as the Reventazon River where their pres-
ence is noted by Branson (1928). In central Panama, coal occurs in
beds of late Oligocene or early Miocene age in the vicinity of La Mesa,
Santiago, Parita, and Macaracas in the provinces of Veraguas, Her-
rera, and Los Santos; in Panama Province south of Capira, and on
the Rio Indio in Colon Province just west of the Canal Zone. Not one
of these occurrences has been successfully exploited, although some of
them have been prospected.

Oil seepages from the early Miocene occur near Garachiné in
Darien Province, Panama, and on Useari Creek and at Uruchico in
the Talamanea valley of Costa Rica. At numerous other places oil
ean be extracted from these shales with chloroform or other solvents.
The presence of these seepages long ago became known to Europeans
and several European and American companies have made geological
investigations, and four companies (Sinclair, Cities Service, Gulf, and
Texas) have engaged in drilling operations, with a total of ten wells
in Panama, and three in Costa Rica. No production has resulted,
although five wells have had shows of oil or gas in the early Miocene,
and one found asphaltic residues in beds of middle or late Miocene
age. The lack of accumulation in commercial quantity is accounted
for by the lack of porous beds in the shale.

No. 23] TERRY: GEOLOGY OF PANAMA 87

BIBLIOGRAPHY

BENIOFF, H.

1949. Seismic evidence for the fault origin of oceanic deeps. Bulletin of
the Geological Society of America, vol. 60, pt. 2, pp. 1837-1856.

BRANSON, E. B.

1928. Some observations on the geography and geology of middle-eastern
Costa Rica. University of Missouri Studies, vol. 3, no. 1, pp. 29-72.

Brown, A. P., and H. A. PILsBRy
1911-1913. Fauna of the Gatun formation, Isthmus of Panama. Proceed-

ings of the Academy of Natural Sciences of Philadelphia, vol. 638,
pp. 336—420, and vol. 64, pp. 500-519.

Carson, J. P.

1874. Geological report on the Darien route and Nercalagua River, Bay
of San Blas. In T. O. Selfridge—Reports of explorations and
surveys to ascertain the practicability of a ship canal between
the Atlantic and Pacific oceans by way of the Isthmus of Panama.
Washington.

CoryELL, H. N., and J. R. EmMsBicu

1937. The Tranquilla shale (upper Eocene) and its foraminiferal fauna.
Journal of Paleontology, vol. 7, no. 4, pp. 285-309.

CorYELL, H. N., and R. W. MossMan

1942. Foraminifera from the Charco Azul formation. Journal of Paleon-
tology, vol. 16, no. 2, pp. 233-246.

Crospsy, I. B.
1942. Geology of the Virilla canyon, Meseta Central Occidental, Costa
Rica. Proceedings of the Highth American Scientific Congress,
Washington, 1940, vol. 4, pp. 483-494.

DALE. We EL:

1912. New species of fossil shells from Panama and Costa Rica. Smith-
sonian Miscellaneous Collections, vol. 59, no. 2, pp. 1-10.

DovuviLLe, H.

1915. Les couches & orbitoides de l’isthme de Panama. Comptes Rendus
Sommaires de la Societe Geologique de France, No. 16, pp. 129-131.

GABB, W. M.

1875. Note on the geology of Costa Rica. American Journal of Science,
third series, vol. 9, no. 51, 198-204, and p. 320.

1881. Descriptions of new species of fossils from the Pliocene clay beds
between Limon and Moen, Costa Rica, together with notes on
previously known species from there and elsewhere in the
Caribbean area. Journal of the Academy of Natural Sciences of
Philadelphia, series 2, vol. 8, pp. 349-380.

88 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

GABB, W. M.—(Cont.)

1895. Informe sobre la exploracién de Talamanca verificada durante los
anios 1873-1874. Anales del Instituto Fisico-geografico Nacional
de Costa Rica, vol. 5, pp. 67-90.

GouDKOoFF, P. P., and W. W. Porter, II

1942. Amoura shale, Costa Rica. Bulletin of the American Association
of Petroleum Geologists, vol. 26, pp. 1652-1655.

GUTENBERG, B., and C. F. RIcHTER

1949. Seismicity of the earth and associated phenomena. Princeton Uni-
versity Press.

HERSHEY, O. H.

1901. The geology of the central portion of the Isthmus of Panama. Bul-
letin of the Department of Geology, University of California, vol.
2, no. 8, pp. 231-267.

HILDEBRAND, S. F.

1938. A new catalogue of the fresh-water fishes of Panama. Zoological
series, Field Museum of Natural History, vol. 22, no. 4, publica-
tion 425.

VsGocj, 1Rh, MEE

1898. The geological history of the Isthmus of Panama and portions of
Costa Rica. Bulletin of the Museum of Comparative Zoology, vol.
28, pp. 154-281.

Howe, E.
1907. Geology and the Panama Canal. Hconomic Geology, vol. 2, no. 7,
pp. 639-658.
JONES, S. M.

1950. Geology of Gatun Lake and vicinity. Bulletin of the Geological
Society of America, vol. 61, no. 9, pp. 893-920.

JOUKOWSKY, E., and M. CLERC
1906. Sur quelques affleurements nouveaux de roches tertiaires dans
Visthme de Panama. Memoire de la Societe de Physique et de
Histoire Naturale de Genéve, vol. 35, pt. 2, pp. 155-178.
KIRKPATRICK, R. Z.

1939. Trigger forces—Canal Zone earthquakes. Bulletin of the Seismo-
logical Society of America, vol. 28, pp. 15-22.

Keren, A. M., and T. F. THompson

1946. Notes on the Gatun formation (Miocene), Panama. Bulletin of the
Geological Society of America, vol. 57, pt. 2, no. 12, p. 1260.

LEMOINE, P., and R. DOUVILLE

1904. Sur le genre Lepidocyclina Gimbel. Memoire de la Societe Geo-
logique de France, Paleontologie, no. 32.

No. 23] TERRY: GEOLOGY OF PANAMA 89

LOHMAN, W.

1934. Stratigraphie des hochlandes von Costa Rica. Geologische Rund-
schau, bd. 25, hft. 1, pp. 10-26.

Maack, G. A.

1874. Report on the geology and natural history of the Isthmus of Choco,
of Darien, and of Panama. In T. O. Selfridge—Reports of ex-
plorations and surveys to ascertain the practicability of a ship
canal between the Atlantic and Pacific oceans by way of the
Isthmus of Darien. Washington.

MacDonatp, D. F.
1913. Isthmian earthquakes. Canal Record, Dec. 10, 1913, pp. 144-149.

1915. Some engineering problems of the Panama Canal... . Bulletin of
the United States Bureau of Mines, no. 86, pp. 88.

1919. Sedimentary formations of the Panama Canal Zone with specific
reference to the stratigraphic relations of the fossiliferous beds.
Bulletin of the United States National Museum, no. 103.

1937. Contributions to Panama geology. Journal of Geology, vol. 45, no.
6, pp. 655-662.

Manross, N. M.

1860. In relation to contract made by the Secretary of the Navy for coal
and other privileges on the Isthmus of Chiriqui. In H. R. 1,
Committee on Naval Affairs, House of Representatives, Wash-
ington, D. C.

McKim, F.
1947. San Blas, an account of the Cuna Indians of Panama; and the
forbidden land, a reconnaissance of the upper Bayano River,
R. P., in 1936. Etnologiska Studier, Etnografiska Museet, no.
15, pp. 185, Goteborg.

OLLER, JOSE
1933. La industria minera en Panama—Segunda Epoca, no. 19, Biblio-
teca Cultura Nacional, Panama.

Ousson, A. A.

1922. The Miocene of northern Costa Rica with notes on its general
stratigraphic relations. Bulletins of American Paleontology, vol.
Senos 39:

1942. Tertiary deposits of northwestern South America and Panama.
Proceedings of the Eighth American Scientific Congress, Geolog-
ical Sciences, Washington, 1940, vol. 4, pp. 231-287.

1942. Tertiary and quaternary fossils from the Burica peninsula of
Panama. Bulletins of American Paleontology, vol. 16, no. 106.

1942. Some tectonic interpretations of the geology of northwestern South
America. Proceedings of the Eighth American Scientific Con-
gress, Geological Sciences, Washington, 1940, vol. 4, pp. 401-416.

90 CALIFORNIA ACADEMY OF SCIENCES [Oc. PAPERS

PALMER, K. V. W.

1923. Foraminifera and a small molluscan fauna from Costa Rica. Bul-
letins of American Paleontology, vol. 10, no. 40.

REEVES, F., and C. P. Ross
1930. A geologic study of the Madden dam project, Alhajuela, Canal
Zone. Bulletin of the United States Geological Survey, no. 821B,
pp. 11-49.
Reip, H. F.
1917. Notes on the Almirante earthquake. Bulletin of the Seismological
Society of America, vol. 7, pp. 27-30.
RIDDELL, G. C.
1927. Is mining to thrive again in Panama? Engineering and Mining
Journal, vol. 124, no. 16, pp. 605-810, and no. 17, pp. 649-653.
ROMANES, J.
1912. Geology of a part of Costa Rica. Quarterly Journal of the Geo-
logical Society of London, vol. 68, pp. 103-159.
SAPPER, K.

1905. Ueber gebirgsbau und boden des siidlichen mittelamerika. Peter-
mann’s Geographische Mittheilungen, erg. 32, hft. 151.

SAPPER, K., and W. STAUB

1937. Mittelamerika, handbuch der regionalen geologie. Carl Winter,
Heidelberg.

SCHUCHERT, C.

1935. Historical geology of the Antillean—Caribbean region, or the lands
bordering the Gulf of Mexico and the Caribbean Sea. pp. 811.
John Wiley and Sons, New York.

SEARS, J. D.

1919. Deposits of manganese ore near the Boqueron River, Panama.
Bulletin of the United States Geological Survey, no. 710C, pp.
85-91.

TAYEOR WE. C.

1852. Substance .of notes made during a geological reconnaissance in
the auriferous porphyry region next to the Caribbean, Sea, in the
province of Veraguas and Isthmus of Panama. Journal of the
Academy of Natural Sciences of Philadelphia, series 2, vol. 2,
pp. 81-88.

TERRY, R. A:
1941. Notes on submarine valleys off the Panama coast. Geographical
Review, vol. 31, no. 5, pp. 377-384.
Touta, F.

1909-1911. Eine jungtertidre fauna von Gatun am Panama-Kanal. Kai-
serlich-kéniglichen Geologischen Reichsanstalt, Jahrbuch, vol. 58,
pp. 673-760, and vol. 59, pp. 487-530.

No. 23] TERRY: GEOLOGY OF PANAMA 91

VAUGHAN, T. W.

1918. Geologie history of the West Indies and Central America during
Cenozoic time. Bulletin of the Geological Society of America, vol.
29, pp. 615-630.

1919. The stratigraphic horizon of the beds containing Lepidocyclina
chaperi on Haut Chagres, Panama. Proceedings of the National
Academy of Sciences, vol. 12, pp. 519-522.

1919. Contributions to the geology and paleontology of the Canal Zone,
Panama, and geologically related areas in Central America and
the West Indies. Bulletin of the United States National Museum,
no. 103, pp. 547-612.

WAGNER, M.

1861. Beitrage zu einer physisch-geographischen skizze des isthmus von
Panama. Petermann’s Geographische Mittheilungen, Ergadnzungs-

heft, pp. 1-25.
1862. Eine reise in das innere der landenge von San Blas und der cor-
dillere von Chepo in der Provinz Panama, ... Petermann’s Geo-

graphische Mittheilungen, pp. 128-141.

WOAKES, E. R.

1899. Modern gold mining in the Darien. Transactions of the American
Institute of Mining Engineers, vol. 29, pp. 249-280.

1923. Darien gold mines. Mining Magazine, London, Nov. 1923.

Wooprine, W. P.

1949. The Panama landbridge. Science, vol. 109, p. 437.

1954. Caribbean land and sea through the ages. Bulletin of the Geo-
logical Society of America, vol. 65, no. 8, pp. 719-732.

1955. Geologic map of Canal Zone and adjoining parts of Panama. United
States Geological Survey, Miscellaneous Geologic Investigations,
Map 1-1. [This map was issued after the present paper was
submitted for publication. |

Wooprine, W. P., and T. F. THompson
1949. Tertiary formations of the Panama Canal Zone and adjoining parts
of Panama. Bulletin of the American Association of Petroleum
Geologists, vol. 33, pt. 1, pp. 223-247.

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