File:Elements of geology - a text-book for colleges and for the general reader (1892) (21069111440).jpg

Title: Elements of geology : a text-book for colleges and for the general reader
Identifier: elementsofgeolog00leco (find matches)
Year: 1892 (1890s)
Authors: LeConte, Joseph, 1823-1901
Subjects: Geology
Publisher: New York : D. Appleton and Co.
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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460 MESOZOIC ERA—AGE OF REPTILES.
Text Appearing After Image:
Fig. 740, Fig. 742. Figs. 740-742.—California Jura-Trias Shells: 740. Grypheea spe- ciosa (after Gabb). 741. Trigonia pandicosta (after Gabb). 742, Ceratites Whitneyi (after Gabb). North Carolina and Virginia—i. e., Upper Triassic. Some of these are given (Figs. 732-739). On the Pacific coast marine life no doubt abounded, as this was the margin of an open sea; but the rocks here are very highly metamorphic, and the fossils, there- fore, mostly de- stroyed. Wherever this is not the case, the rocks abound in fossils. In Hum- boldt County, Ne- vada, for example, the strata in some places seem almost wholly made up of Ceratites Whitneyi (Fig. 742). In the same locality the remains of an Enaliosaur (sea-saurian) have been found. On account of the marine conditions prevalent, the two peri- ods are easily separable on the Pacific coast. Recent Discoveries.—Very recently in Colorado and Wyoming, in beds which are referred to the Uppermost Jurassic, a large number of most extraordinary reptiles have been found and described by Marsh and Cope. Also, in the Wyoming beds, Marsh has discovered some twenty-five species of Marsupial mammals and a reptilian bird (Lao- pteryx). The beds from which all these have been taken are called, from their most abundant and characteristic form, the Atlantosaur beds. These discoveries are treated sepa- rately, not only on account of their great importance, but also and especially because they belong to an en- tirely different horizon, viz., the uppermost Jurassic, passing into the Cretaceous.* Dinosaurs.—The most abundant and the largest reptiles found here are Dinosaurs. Some ten or twelve species of this order have been described by Cope, and fifteen or twenty species by Marsh. Some of these are Fig. 743.—Dorsal ver- J x J tebra of Ccelurus from the east slope of the Colorado Mountains, but fraguts, trans- , verse section (af- the most important have been found on the west slope. ter Marsh).

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