DAVIS. — ROCKY MOUNTAIN TERTIARIES. 363 



mus, ox, horse, antelope, crocodile, and various fish. The borings yield 

 pebbles, sands, and clays, with peat and wood, and remains of terrestrial 

 mammals, fluviatile reptiles, and fresh-water molluscs. 



Still more pertinent to the present discussion is the account given of 

 the inclined strata of the Siwalik (Tertiary) formation in the Himalayan 

 foot-hills (Ibid., 356-368). "The lower portion of the system is char- 

 acterized by a great thickness of fine grained grey, micaceous, pepper and 

 salt sandstone, iuterbedded with clay bands near its lower portion, while 

 the upper part of the system is composed of soft earthy clays, undistiu- 

 guishable from the alluvium of the plains, . . . and coarse conglomerates 

 of well rounded pebbles and boulders " (356). These strata are much 

 tilted; their thickness is estimated at 14,000 or 15,000 feet. The ver- 

 tebrate fauna of the Siwalik formation is well known to paleontologists. 

 " The earlier observers regarded this great series of beds as having been 

 deposited in a sea, a supposition which is sufficiently disproved by the 

 complete absence of any marine organisms, and by the occurrence of the 

 remains of fresh water molluscs, fishes, and tortoises. It is hardly possi- 

 ble that they could have been deposited in a fresh water lake, for it is 

 not conceivable that a fresh water lake extending the whole lengih of the 

 Himalayas could have existed. Moreover, the fresh water organisms 

 whose remains have been found are all such as inhabit streams, and not 

 lakes. The very close resemblance between the upper Siwalik beds and 

 the recent deposits of the Gangetic plain leaves little room for doubt that 

 thfe Siwalik beds were deposited subaerially by streams and rivers " (358). 

 While it does not seem necessary to deny the possibility of conceiving 

 the existence of a lake all along the base of the Himalayas, the necessity 

 for believing in such a lake seems to be removed by the striking re- 

 semblance between the upturned Siwalik strata and those of the Indo- 

 Gangetic plain. 



11. Fluviatile Deposits of the Great Plains. — In view of these various 

 considerations and examples bearing on the competence of rivers to form 

 extensive stratified deposits of fine as well as of coarse texture, there 

 seems little room for doubt that some part of the fresh-water Tertiary 

 formations that stretch forward from the Rocky mountains across the 

 open slope of the Great Plains may be of fluviatile and not lacustrine 

 origin. The first observer to reach this conclusion was Gilbert, whose 

 views are to be found in a report on underground water in eastern Colo- 

 rado (17th Ann. Rep., U. S. G. S., 553-601). He ascribes the Tertiary 

 strata that unconformably overlie the Cretaceous of the Plains chiefly to 

 river action, but partly to transportation by wind and to deposition in 



