The Geological History of PlantsDawson, John William, Sir
Science
The Geological History of Plants
Dawson, John William, Sir
Paleobotany
The above presents some interesting new types not heretofore found in the
Middle Cretaceous. More especially the occurrence of large flowers of the
composite type presents a startling illustration of the early appearance
of a very elevated and complex form. Great interest also attaches to
these Amboy beds, as serving, with those of Aix and Greenland, to show
that the margins of the Atlantic were occupied with a flora similar to
that occurring at the same time in the interior plateau of North America
and on the Pacific slope.
The beds at Aix-la-Chapelle are, however, probably somewhat newer than
the Dakota or Amboy beds, and correspond more nearly in age with those
of the Cretaceous coal-field of Vancouver Island, where there is a
very rich Upper Cretaceous flora, which I have noticed in detail in
the "Transactions of the Royal Society of Canada."[DP] In these Upper
Cretaceous beds there are fan-palms as far north at least as the latitude
of 49°, indicating a very mild climate at this period. This inference
is corroborated by the Upper Cretaceous flora of Atané and Patoot in
Greenland, as described by Heer.
[DP] Vol. ii., 1884.
The dicotyledonous plants above referred to are trees and shrubs. Of the
herbaceous exogens of the period we know less. Obviously their leaves
are less likely to find their way into aqueous deposits than the leaves
of trees. They are, besides, more perishable, and in densely wooded
countries there are comparatively few herbaceous plants. I have examined
the beds of mud deposited at the mouth of a woodland streamlet, and have
found them stored with the fallen leaves of trees, but it was in vain to
search for the leaves of herbaceous plants.
[Illustration: Fig. 76.--_Brasenia antiqua_. Upper Cretaceous, South
Saskatchewan River. Natural size, _a_, _b_, Diagrams of venation,
slightly enlarged.]
The climate of North America and Europe, represented by the Cenomanian
vegetation, is not tropical but warm temperate; but the flora was more
uniform than at present, indicating a very equable climate and the
possibility of temperate genera existing within the Arctic circle, and it
would seem to have become warmer toward the close of the period.
The flora of the Cenomanian is separated in most countries from that of
the Senonian, or uppermost Cretaceous, by a marine formation holding few
plants. This depends on great movements of elevation and depression, to
which we must refer in the sequel. In a few regions, however, as in the
vicinity of the Peace River in Canada, there are plant-bearing beds which
serve to bridge over the interval between the Early Cenomanian and the
later Cretaceous.[DQ]
[DQ] See paper by the author in the "Transactions of the Royal Society of
Canada," 1882.
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