A. P. (Arthur Philemon) Coleman.

Elementary geology with special reference to Canada online

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Cretaceous formations are distinctly marine and point to a
very extensive flooding of the continent.

In North America, the break between the Lower and Upper
Cretaceous is still more profound ; indeed, it is so marked that
American geologists separate the strata into two distinct
u 305



306 ELEMENTARY GEOLOGY

systems Comanchian and Cretaceous believing that the
break is comparable in magnitude with those that separate
the other great systems. While this subdivision is doubtless
better in accord with the facts as revealed in North America,
it seems inappropriate, nevertheless, to introduce a new
systemic name for strata that are admittedly to be correlated
with the Lower Cretaceous rocks of Europe. In this work we
shall regard the lower series as "Lower Cretaceous," but in
deference to the opinion of many eminent American geologists,
the term "Comanchian" will also be employed.

This general discussion of the Cretaceous period cannot be
concluded without reference to the English chalk. The "White
Cliffs of Albion," famous in history and song, are composed of
chalk of Upper Cretaceous age. This formation is the most
conspicuous member of the Mesozoic strata of Europe, and is
referred o as The Chalk. Nearly the whole of the Upper
Cretaceous rocks of England belong to this series, which is
divided into three subdivisions the Lower, Middle, and Upper
Chalk. The stone is composed of enormous numbers of the
minute calcareous shells of Protozoa (foraminifers) mingled
with fragments of the shells of other organisms. Nodules
of flint are common, more particularly in the Upper Chalk.
Such a formation could have been made only under typical
marine conditions in a sea into which no sediments were
being discharged.



PHYSICAL EVENTS OF THE CRETACEOUS IN
NORTH AMERICA

We have seen that the whole of eastern North America
remained land throughout the Jurassic period, and we may
conclude that it suffered a large amount of dissection and
erosion. The products of this erosion were carried out to sea
and are still beneath the waters of the Atlantic. Even in
Lower Cretaceous time the sea did not invade the present
land area, but changes in the coast-line made possible the
accumulation of continental deposits along the coastal region.
Lower Cretaceous continental deposits are found more par-
ticularly in Maryland, Virginia, and Georgia.



THE CRETACEOUS PERIOD 307

At the same time continental deposits were formed in
limited areas in the western states, more particularly in
Colorado and Wyoming. These beds (Morrison formation)
are of particular interest as they have revealed some of the
most remarkable dinosaurs yet discovered.

Depression of the continent in Lower Cretaceous time,
which permitted the advance of the sea and the deposition
of marine deposits, occurred over a wide area in the south-
western states, Mexico, and Central America. This series of
deposits is the Comanchian proper. Marine invasions also
occurred on the Pacific border, in British Columbia, Oregon,
Washington, and California.

Owing to the great importance and significance of the
deposits of the Gulf region and Mexico, the local name,
Comanchian, has been elevated to the dignity of a time- term
of systemic rank, and is applied by American geologists to
all Lower Cretaceous formations.

Throughout the world, the Upper Cretaceous is marked by
one of the most extensive floodings of the continental areas
known in geological history. In North America, the eastern
border of the United States, the region surrounding the Gulf
of Mexico, and a wide strip of the Pacific coastal region were
submerged. In addition, and of still greater importance, was
a depression of the interior continental region whereby the
sea covered a wide belt of west-central North America from
the Arctic ocean to the Gulf of Mexico.

In the extreme west of the continent, terrestrial disturbances
were marked throughout the Cretaceous. The most important
movement in the Lower Cretaceous was the elevation of a
long strip of country extending from Alaska to Central
America. The axis of elevation lay some distance east of
the coast and passed through the central region of British
Columbia. The elevation of this strip probably occasioned a
downwarping on either side, and prepared the way for the
advance of the Upper Cretaceous sea into the interior of
the continent and over the region immediately bordering
the Pacific.

Upper Cretaceous time continued to be a period of uplift
and of volcanic activity in the Cordilleran region. Towards
the close of the period the uplifting forces reached a climax



308 ELEMENTARY GEOLOGY

of intensity deserving the name revolution, which is applied
only to terrestrial disturbances on the grandest scale.

In order to better understand the results of this revolution,
it is advisable to review the history of the area affected. We
have seen that in the early Cambrian a trough was formed to
the east of the old Pre-cambrian lands which constituted the
Pacific border of the continent. In this trough sedimentation




FIG. l6o. SKETCH MAP OF NORTH AMERICA IN CRETACEOUS TIME

continued through nearly all the Palaeozoic era. The sea
partially withdrew in the Triassic, but returned in the Jurassic
and Lower Cretaceous periods, adding to the great thickness
of strata already formed in the Rocky Mountain geosyncline.
The mid-continental sea of the Upper Cretaceous overlapped
this region and still further increased the thickness of the
sediments, which are not less than 50,000 feet and probably
much more in total thickness.

It was this region, so long an area of sedimentation, that



THE CRETACEOUS PERIOD 309

was chiefly affected by the revolution at the close of the
Cretaceous. A great thrust acting from the direction of the
Pacific ocean threw the region into immense folds with a
general north-west and south-east trend. These folded masses
of rock were elevated to great heights, crumpled and broken ;
great faults developed in places; and immense masses were
pushed, in some cases for miles, out of their original position.
This great event is known as the Laramide revolution; it
marks the birth of the Rocky mountains and the close of
Mesozoic time.

In other parts of the world mountain-making forces were
at work at the same time. The Appalachians of eastern North
America were re-elevated, the Andes of South America were
formed, and general elevation and mountain-building occurred
in the Old World.



THE CRETACEOUS SYSTEM IN CANADA

In eastern Canada no Cretaceous strata, either continental
or marine, are known. The Upper Cretaceous transgression
which affected the eastern border region of the United States
did not advance as far north as Canada.

In western Canada rocks of this age are of great importance:
their description can be best given under the following four
areas of distribution:

i. THE GREAT PLAINS AREA. The region occupied by the
Cretaceous rocks in the prairie region of western Canada may
be roughly defined as a great triangle, stretching along the
international boundary for 750 miles from the centre of
Manitoba to the foothills of the Rocky mountains and reach-
ing an apex 1000 miles to the north-west in the south-east
corner of Yukon territory. While Cretaceous strata were
undoubtedly formed over the whole of this area, they do not
form the surface rock throughout, as they have been covered
by later formations to a limited extent. The chief of these
areas of later rocks are in southern Saskatchewan and in
western Alberta.

The greater part of the region is covered with a thick
accumulation of glacial and post-glacial deposits which hides



310 ELEMENTARY GEOLOGY

the rocks except where deep river valleys have been cut
through the soils or where the flanks of minor elevations
have been eroded.

The rocks of this area were formed in the great shallow sea
of Upper Cretaceous age which covered the heart of the
continent. This sea was doubtless subject to many minor
fluctuations which resulted in local deposits, and in its later
stages, particularly in the western part, it passed into the
condition of brackish and even freshwater lakes. Owing to
the above facts and the scattered nature of the accessible
exposures, it has not yet been possible to accurately correlate
all the formations of this great region.

The Upper Cretaceous rocks of this area may be arranged
in three divisions, erroneously but usually called "groups,"
above which lies a fourth division of less magnitude, as
follows :

Edmonton formation.

Montana group.

Colorado group.

Dakota group.

The Dakota group in Canada is composed essentially of
sandstone which is largely of freshwater origin. Exposures
of the rock are of rather rare occurrence: the most typical
are to be seen in the valleys of the rivers entering Lake
Winnipegosis from the west. The stone is soft, incoherent,
and of no particular value.

The Dakota, if it occurs, is so deeply buried under the later
rocks all the way across the prairies that it is not seen again
until brought to the surface by the folding which produced
the foothills of the Rocky mountains. Exposures may be
seen in the coal-mining districts of the foothills and in the
lengthwise valley west of the first great range of mountains.
At the Sweetgrass hills in Montana, just south of the inter-
national boundary, the Dakota group is much better exposed
than at any point in Alberta. The section shows more than
500 feet of shale, sandy shale, and sandstone. The stone of the
mountains differs greatly from that of Manitoba, as it is very
hard and of green or bluish-green colour. At so great a
distance from the Manitoba outcrops it is questionable



THE CRETACEOUS PERIOD 311

whether this formation is to be strictly correlated with the
eastern sandstone.

The Colorado group is divisible into two formations a
lower (Benton) and an upper (Niobrara). Exposures occur in
Manitoba and in the foothills, but across the Great Plains the
formations are covered by the rocks of the Montana group.
As revealed by bore-holes in southern Alberta the group is
nearly 2000 feet thick, but the average is probably much less.




FIG. l6l. SKETCH MAP SHOWING THE CRETACEOUS AND TERTIARY ROCKS
OF THE GREAT PLAINS

Cretaceous, black; Mixed Cretaceous and Tertiary, dotted; Tertiary, the white areas
within the black. The Cretaceous and Tertiary of British Columbia not shown.

The Benton formation consists essentially of shale and there
is much soft clay carrying a large amount of colloidal silica.
This material (bentonite) has a remarkable property of re-
taining water, which makes it a very valuable constituent of
the soils derived from the decay of the Benton shales and
other formations.

The Niobrara formation also is largely composed of clay
or shale, but it is much more calcareous than the Benton shale
and even contains thin layers of limestone in places. The form-
ation is recognised with certainty only in the eastern exposures.



312 ELEMENTARY GEOLOGY

The areal extent of the Dakota and Colorado groups is
insignificant when compared with that of the Montana group,
which forms the surface rock over nearly the whole of the
Cretaceous region of the Great Plains. There are two facies
of Montana deposits : marine, and brackish to freshwater. In
the eastern part of the region, the marine facies, Pierre forma-
tion, is alone developed, but in the west the brackish water
deposits, Belly River formation, occur between an upper and
a lower series of marine strata. The Pierre formation is mostly
shale, and much of it presents the same colloidal properties as
the Benton shale. The Belly River beds are composed of soft
sandstones and shales.

The Edmonton formation is very similar to the Belly River
in the character of its rocks, consisting of soft, incoherent
sandstones, sandy shales, and shales. The formation overlies
the upper marine beds of the Pierre over a considerable area
in central Alberta.

The conditions of shallow and brackish water under which
the Belly River and Edmonton beds were deposited favoured
the formation of layers of coal. Owing to the relatively short
lapse of time and the lack of severe terrestrial disturbances
since the beds were formed, coal-forming has not proceeded
beyond the earlier stages; in consequence, nearly all the
coal is lignitic or sub-bituminous. At Lethbridge, however,
the coal is of bituminous grade.

In the Belly River formation Bowling estimates that 33,192
square miles are underlaid by coal beds which contain a
reserve of 223,358,000,000 metric tons. The principal mines
are situated in the vicinity of Lethbridge, Alberta. The same
authority estimates a maximum reserve of 800,958,000,000
metric tons and a more certain reserve of 383,697,000,000
metric tons in the Edmonton formation. The chief collieries
are near Drumheller on the Red Deer river, near Edmonton,
and in the foothills.

The importance of the colloidal clays has already been
referred to. The water-holding clay soils (gumbo) owe their
valuable property of retaining moisture to the hydrated silica
derived from the decay of Benton and Pierre shales.
These colloidal clays are not suitable for brick-making,
but some of the upper non-colloidal clays of the Pierre



THE CRETACEOUS PERIOD 313

(Odanah) as well as the brackish water clays are used for
this purpose.

Natural gas is another important product from the Creta-
ceous formations, more particularly of Alberta. The gas
reservoirs are in the Dakota sandstone; they are tapped by
deep holes through the overlying strata, more particularly
at Medicine Hat and Bow island. Far to the north, on the
Athabasca river, are the so-called tar-sands sandstones of
Dakota age highly impregnated with bitumen : they are thought
to represent a future source of important industrial products.

2. THE ROCKY MOUNTAIN AREA. We have seen that the
Rocky Mountain geosyncline was an area of sedimentation in
the Lower Cretaceous. The strata consist of an upper and a
lower sandstone with coal-bearing measures between. The
presence of beds of coal and fossil plants indicates that this
series, the Kootenay, is of freshwater origin. The greatest
thickness, nearly 4000 feet, is along the main axis of the
Rocky mountains; eastward, the strata thin out rapidly and
are overlapped by Upper Cretaceous rocks. The upraising of
the mountains at the close of the Cretaceous affected all these
rocks, but subsequent erosion has removed them from the
summits of the ranges. Kootenay strata, therefore, are found
to a limited extent in the foothills, but on a larger scale in
the valleys between the more easterly ranges of the mountains.

The coal of the Kootenay formation is a high-grade bitu-
minous, ranging to anthracite in places. Numerous fields
occur in the long narrow valleys between the ranges; the
most important is the Crowsnest field in British Columbia, in
which the reserve is estimated at more than 56,000,000,000
metric tons, with a workable reserve of 23,000,000,000 metric
tons. The centre of this field is Fernie, British Columbia.
The more important coal-mining centres on the Alberta side
of the boundary are at Coleman on the Crowsnest line, and
at Bankhead on the main line of the Canadian Pacific Railway.

3. INTERIOR PLATEAU AREA OF BRITISH COLUMBIA. In
the interior of British Columbia, between the Coast Range and
the Columbia mountains, are many disconnected areas of
coarse sediments of Cretaceous age ; these are generally mixed
with contemporaneous volcanic matter. In northern British
Columbia coal fields occur in these areas. .



314 ELEMENTARY GEOLOGY

4. PACIFIC COAST AND ISLANDS AREA. Fossiliferous sand-
stones, shales, and conglomerates of Upper Cretaceous age
constitute the Queen Charlotte series, which carries workable
beds of coal on the islands and is known to occur elsewhere.

On the north-east side of Vancouver island and on the
adjacent small islands of the Strait of Georgia, Upper
Cretaceous sandstones and shales, the Cowichan group, are
well exposed. Coal mines of considerable importance are
worked in these rocks at Nanaimo, Comox, and other places
in the vicinity. Excellent sandstone for building purposes
is quarried on Gabriola, Saturna, and other islands of the
Strait of Georgia.



LIFE OF THE CRETACEOUS
CRETACEOUS PLANTS

In Lower Cretaceous time the vegetation shows the same
predominance of cycads that characterised the Jurassic
period; in the upper division, however, the angiosperms, or
higher flowering plants, begin to assert the supremacy they
still enjoy. In late Lower Cretaceous time cycads and conifers
began to wane and trees like the sassafras and poplar appeared.
Before the close of the Upper Cretaceous the flora was dis-
tinctly of modern aspect, with species of birch, maple, oak,
walnut, and many other familiar trees. With these plants
were mingled species of magnolia, fig, and cinnamon, indi-
cating a warmer climate.

The brackish water beds of western Canada have furnished
the remains of a long list of plants : probably the most striking
fossils are the large silicified trunks of a species of cypress
which are common in the Edmonton formation of Alberta.

CRETACEOUS INVERTEBRATES

PROTOZOA reach a high degree of development, as the
remains of these minute organisms form a large part of the
Chalk of Europe. The more calcareous parts of the Niobrara
formation of Manitoba contain numerous protozoans.

SPONGES, both siliceous and calcareous, are common in the



THE CRETACEOUS PERIOD



315



Cretaceous of Europe, but in North America they are of less
frequent occurrence. The flints of the English Chalk are
formed by the accretion of dissolved silica derived from the
spicules of siliceous sponges.

CORALS are abundant in the Cretaceous rocks of some
regions, but they are rare in Canada. The conditions under
which the prevailing shales were deposited did not favour the
life of corals.

ECHINODERMS are represented chiefly by sea urchins which
show an advancing tendency to irregular form. The peculiar
stemless Uintacrinus
with remarkably long
arms is a characteristic
fossil of the Cretaceous
of Kansas. Hemiaster
Humphrey 'sianus is the
only sea urchin from the
Upper Cretaceous rocks
of the Great Plains, and
is of rare occurrence.

PELECYPODS are very
numerous, and some
peculiar forms are par-
ticularly characteristic
of Cretaceous time: of
these, Hippurites and FIG ' l62 ' CRETACEOUS CRINOID

* Uintacnnus sociahs. Much reduced.

related forms, with one

valve extremely small and placed like a cover on the
larger valve, are eminently Cretaceous. The commonest
genera in the marine Cretaceous rocks of western Canada
are Arctica, Inoceramus, Gervillia, Pteria, Ostrea, and
Liopistha. The brackish water beds of the Belly River series
are in places crowded with oysters : Corbula and Corbicula are
also very abundant.

GASTROPODS are numerous and show a normal advance on
the Jurassic type, but they present no especial features for
general comment. Anisomyon, Lunatia, and Anchura are
perhaps the commonest Canadian genera.

CEPHALOPODS are represented by many belemnites and
ammonites. The former require no particular mention, but





FIG. 163. CRETACEOUS PELECYPODS

Arctica ovata alia ; 2. 'Arctica ovata; 3. Ostrea subtrigonalis ; 4. Ostrea glabra ; 5.
Inoceramus barabini ; 6. Pteria linguifera ; 7. Liopistha undata ; 8. Corbula per-
angulata ; 9. Pteria nebrascana ; 10. Corbicula occidentalis ; n. Protocardia borealis ;
12. Volsella meeki ; 13. Modiola attenuata. All figures six-sevenths natural size. After
Whiteaves, Meek and Hayden, and from original photographs.




FIG. 164. CRETACEOUS PELECYPOD

Slab of red Cretaceous sandstone from the Red Deer river, Alberta, with Inoceramus vanuxemi.
One-fourth natural size.




FIG. 165. CRETACEOUS GASTROPODS

i. Campeloma producta ; 2. Melania insculpta ; 3. Anisomyon centrals ; 4. Viviparus leai;
5. Anchura americana ; 6. V anikoropsi<> tuomeyanu ; 8. Lunatia concinna. All figures
about natural size. From Meek and Hayden and from photographs of species from western
Canada.



3i8 ELEMENTARY GEOLOGY

the latter show evidence of decadence. While many typical
ammonites with closely coiled shell still survive, the senile
condition of the race is indicated by the assumption of peculiar
form. Instead of the typical coiled shell, we find straight
(Baculites), hook-shaped (Hamites), open-coiled (Crioceras),
turreted (Turrilites), and many other erratic forms. This
tendency to strange shape seems to be the precursor of
extinction, for no ammonites are known after the Cretaceous.

One of the commonest fossils of our western Cretaceous is
the straight-shelled Baculites, of which several species are
known. The fragments of this fossil are commonly mistaken
for fish. A very large ammonite, Placenticeras whitfieldi, is
also a common fossil in the Cretaceous of the plains. The
Upper Cretaceous strata of Vancouver and Queen Charlotte
islands have yielded a rich and varied ammonite fauna.

ARTHROPODS are well represented and show a great increase
in the broad-shelled decapods or crabs. These fossils are rare
in the Montana group of the plains, but ten species are known
from the Cowichan rocks of Vancouver island.



CRETACEOUS VERTEBRATES

FISH show a pronounced change in Cretaceous time, as the
old type with skeleton of cartilage gradually gives place to
the teleosts with true bony skeleton and thin, flexible, over-
lapping scales. In other words, the modern type of fish gains
an ascendancy over the typical Mesozoic type, and is repre-
sented, before the close of the period, by such familiar fish
as salmon, herring, and other common forms. Some of the
Cretaceous fish were of great size and predaceous habits:
Portheus was twelve to fifteen feet in length and the mouth
was armed with a truly formidable series of teeth. Sharks
were still numerous and were closely related to modern types.

REPTILES. The Cretaceous system equals and probably
exceeds the Jurassic in the number and variety of the
reptilian remains. The inclusion of the famous Morrison
beds of Wyoming and Colorado in the Cretaceous transfers
to this system many of the largest and best known dinosaurs
which were formerly believed to be of Jurassic age.

Ichthyosaurs resembling those of the Jurassic occur, but



THE CRETACEOUS PERIOD 319

less frequently, in the Lower Cretaceous: they do not survive
the middle of the Upper Cretaceous.




FIG. 166. CRETACEOUS ECHINIDS AND CEPHALOPODS

Baculttes ovatus, specimen from Peace river with the outer shell; 2. Baculites sp. with the
outer shell removed showing the sutures; 3. Hemiaster humphreysianus ; 4. Scaphites
subglobosus; 5. Placenticeras whitfieldi. Reduced. After Whiteaves and Meek.

Plesiosaurs are more abundant in Cretaceous than in
Jurassic time : they reach their maximum development in the
later part of the period and survive until its close. Some of



ELEMENTARY GEOLOGY

these creatures were of great size: the head of the largest
form known was about five feet long, and the smallest species
was fully ten feet in length. Elasmosaurus platyurus, the




FIG. 167. UPPER CRETACEOUS PLESIOSAUR

Elasmosaurus platyurus with an ichthyosaur, flying reptiles, and the diving bird Hesperornis.
From Williston, " Water Reptiles, Past and Present."

longest-necked plesiosaur, shows the following proportions:
head, two feet; neck, twenty- three feet; body, nine feet;
tail, seven feet.




FIG. 168. CRETACEOUS MOSASAUR

Thylosaurus dyspelor, one-nineteenth natural size. From " Memoirs of the American
Museum of Natural History."

While the remains of plesiosaurs are not particularly
numerous they have, nevertheless, been recorded from all
parts of the world where marine Cretaceous strata occur.
Cimoliosaurus magnus from the Belly River formation of
Alberta is the only Canadian example.



THE CRETACEOUS PERIOD



321



A new type of aquatic reptile appeared in the Upper
Cretaceous and existed in large numbers in many parts of
the world. Thousands of specimens have been obtained from
the chalk beds of ....
Kansas alone. These
creatures, known




THE GREAT AMPHIBIOUS DINOSAUR
Brontosaurus excelsus.



as mosasaurs, were

very long - bodied,

almost snake-like,

and were provided FIG. 169.

with four " paddles ' '

or modified limbs differing greatly from those of ichthyosaurs

and plesiosaurs. The structure of the skeleton is very peculiar,

and indicates a totally different ancestry from that of the

other aquatic reptiles. They were not unlike the mythical

sea-serpent. In size the known forms range from eight to


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Online LibraryA. P. (Arthur Philemon) ColemanElementary geology with special reference to Canada → online text (page 23 of 26)