470 Revieivs — Clarence King — Surrey of Fortieth Parallel. 



others (based on the plant-remains) to the Tertiary, or considered as 

 a transition member between the Cretaceous and Tertiary. Although 

 containing the facies of a Tertiary flora, this is associated with 

 Dinosaurian reptiles characteristic of Mesozoic age, which, together 

 with a period of immense disturbance at the close of the Laramie 

 beds and complete nonconformity of the overlying series of purely 

 freshwater shale, should constitute a division between the Mesozoic 

 and Tertiary. " It will be seen," says the author, " that the strati- 

 graphical break, with its unmistakable Eocene facies at the base of 

 the one group, and the Dinosaurian reptiles at the close of the other, 

 marks the period of nonconformity as distinctly at the close of the 

 Cretaceous." 



The fauna up to the base of the Laramie is strictty marine. The 

 Laramie itself carries the remains of an estuarine or brackish water 

 life, associated with strictly Mesozoic saurians. 



With the close of the Cretaceous the conformable series of marine 

 and estuarine deposits came to an end, and was immediately followed 

 by one of the most important orographical movements of the whole 

 Cordilleran history. The most important result of this post-Cre- 

 taceous movement was the elevation of the whole interior of the 

 continent and the complete extinction of the inter- American Medi- 

 terranean Ocean. 



From the date of this movement no marine waters have ever 

 invaded the middle Cordilleras, and the subsequent strata are all of 

 lacustrine origin. The Eocene of the Fortieth Parallel region was a 

 period of four lakes, whose deposits — unconformable among them- 

 selves — amount to 10,000 feet, and are characterized by an abundant 

 series of vertebrate life. At the close of the Eocene an important 

 orographical movement took place by which the province of the 

 northern Great Plains, and a long narrow tract lying on the eastern 

 base of the Sierra Nevada and the present Cascade Kange became 

 depressed and received the drainage of the surrounding countries, 

 forming two extended Miocene lakes. The deposits of the western- 

 most lake are chiefly the tuffs and re-arranged ejecta of volcanic 

 eruption ; the deposits of the plains are the simple detritus from the 

 sui'rounding lands. 



Another orographical movement followed the close of the Miocene, 

 affecting differently the areas of the western and eastern lakes, so 

 that the Pliocene opened with two enormous lakes, one covering the 

 basin country of Utah, Nevada, Idaho, and eastern Oregon, the other 

 occupying the province of the plains. Both of these Pliocene lakes, 

 as do the Miocene, contain the remains of rich faunas. The extent 

 of the Tertiary exposures are seen in Map IV., and the sequence of 

 the Tertiary lakes at p. 458. The close of the Pliocene period was 

 signalized by another considerable movement, which affected 

 differently the area occupied by its sediments, and was followed by 

 the varied series of deposits of the Quaternary age, described in 

 Section V. (pp. 459 — 529), which is full of interesting matter, not 

 only as relating to glacial phenomena and the lake deposits of the 

 period, but also as to the structure and origin of the remarkable 

 gorges or canons, which are wholly within this period. 



