FOSSIL FISHES. 239 



The remains of fishes were found at a few localities in the upper lacus 

 tral clays exposed in the Truckee Canon. No determination of these fossils 

 has been made, farther than the fact that they belonged to Teleost fishes of 

 considerable size. They probably indicate that the ancient lake was not 

 strongly alkaline or saline, but, on the other hand, they are not proof that 

 it was fresh ; as a number of the brackish lakes of the Great Bxisin at 

 the present time are abundantly stocked with fish. Little weight can be 

 attached to these fossils, however, in determining the character of the former 

 lake, for the reason that they might have been contributed by inflowing 

 streams even though the water of the lake was a strong brine. Dead fish 

 are sometimes found floating in Great Salt Lake, Utah, which must have 

 come from the inflowing streams. These are preserved for a long time by 

 the brine of the lake but must eventually become buried in the sediments 

 now forming at the bottom of the basin, and, when fossilized, will, in a cer- 

 tain sense, form a false entry in the geological records. 



During our examination of the Lahontan basin, fossil shells were ob- 

 tained at a large number of localities, and in many instances were found in 

 great abundance. Both the fossil and recent mollusks collected, together 

 with the similar material previously obtained by Mr. Gilbert from the Bon- 

 neville basin, were studied by Mr. R. Ellsworth Call, who also paid a brief 

 visit to each of the ancient lake basins during the summer of 1883, for the 

 purpose of increasing the collections and making himself personally familiar 

 with the peculiarities of the region. The results of Mr. Call's investiga- 

 tions have been published as Bulletin No. 11 of the Reports of this Survey, 

 to which the reader is referred for detailed information in reference to the 

 fossil shells mentioned in the present volume. Besides the shells inclosed 

 in tufas and lacustral sediments there are others, termed semi-fossil, which 



certainly followed the disappearance of the Quaternary lakes of the Far West, and, so far as that re- 

 gion is concernedj this would furnish a sufficient cause for the extinction of the large mammals 

 which were formerly ahundant. This hypothesis is open to ohjections, however. Evidence that an 

 arid climate succeeded the Glacial epoch in the eastern portion of this continent has not been recognized. 

 Even if it could be shown that a period of extreme aridity preceded the present climate, it is difficult 

 to understand why certain mammals, as the elephant, mastodon, horse, camel, megalonyx, etc., 

 should have become extinct, while others no more capable of withstandiug great changes of environ- 

 ment should have survived. The recent extinction of a number of mammals is an enigma the solu- 

 tion of which would reflect much light on the mutatious of faunas during the older and still more 

 obscure portions of geological history. 



