CONTINENTAL DEPOSITS OF ROCKY MOUNTAIN REGION 597 



The marvel is not in the fact that here and there we find the vestiges of a great 

 lake, but that we find those vestiges everywhere. The whole region, with the ex- 

 ception of the mountain platforms and the preexistent mainlands, has passed 

 through this lacustrine stage."* 



The occurrence of numerous lakes is made by the same author the basis of in- 

 ferences concerning Tertiary climate : " We know that the Miocene climate of the 

 West was moist and subtropical. This is indicated by the great extent of fresh- 

 water lakes in some portions of the West, their abundant vegetable remains, and 

 the exuberance of land life." t Another author of great experience in the Rocky 

 Mountain region wrote that the preservation of numerous vertebrate fossils was 

 "probably, without exception, due to their entombment beneath the waters of 

 the great fresh- water lakes which existed in this [Colorado] region during Mesozoic 

 and Cenozoic time." J 



From the first recognition of the Pliocene of the Great plains and its interpreta- 

 tion as a lacustrine formation, it has been taken to date one of the broad uplifts 

 by which the Rocky Mountain region has gained its present height, for " the in- 

 clined plane of the whole system of the Great plains received its slope by me- 

 chanical tilting subsequent to the deposition of the Pliocene strata." $ 



Again, "movements of elevation are indicated by both Tertiary and Pleistocene 

 deposits that have a lacustrine origin, since the present elevation of the plains 

 region, which shows an average descent in round numbers of 10 feet to the mile 

 from the foothill region to the valleys of the Missouri and Mississippi, would not 

 admit of the holding of lake waters on its surface." || 



The Tertiary lakes of the Rocky Mountain district have become stock subjects 

 of geological teaching, if one may judge by the unqualified statements concerning 

 them in the text-books generally in use. Dana, Le Conte, Scott, and Tarr all assert 

 the existence of these lakes without demur. Similar statements are naturally made 

 by the standard European text-books, such as those by Geikie, de Lapparent, and 

 Oredner. 



It is interesting to review the literature of this subject with the object of dis- 

 covering how the theory of the lacustrine origin of the western Tertiaries was in- 

 troduced, on what evidence it was based, and how thoroughly this evidence was 

 discussed. 



Introduction op the Lake Theory 



The early volumes of Hayden's surveys afford such sentences as the following: 

 " With the commencement of the Tertiary was ushered in the dawn of the great 

 lake period of the West. The evidence seems to point to the conclusion that from 

 the dawn of the Tertiary period, even up to the commencement of the present, 

 there was a continuous series of fresh-water lakes all over the continent west of 

 the Mississippi river. . . . The earliest of these great lakes marked the com- 

 mencement of the Tertiary period, and seems to have covered a very large portion 

 of the American continent west of the Mississippi, from the Arctic sea to the isthmus 

 of Darien. . . . Every year, as the limits of my explorations are extended in 



* Tertiary History of the Gi-and Canon District, p. 216. 



-f-Ibid., p. 223. 



X U. S. Geol. Survey Monograph, vol. xxvii, p. 525. 



§ Fortieth Parallel Survey, vol. i, p. 489. 



|| U. S. Geol. Survey Monograph, vol. xxvii, p. 40. 



