628 IDAHO MINING DISTRICTS. 



evidence clearly indicates a Pliocene age. From the same beds 

 were obtained three species of crawfishes specifically distinct from 

 all others described from the West. Mammalian remains were also 

 collected by King from similar beds on Sinker Creek, which were 

 determined by Leidy to be Mastodon mirificus and Equus excelsus, 

 both of which belong to the Niobrara Pliocene fauna. A few mol- 

 lusks have also been found in the same deposits on Sinker Creek. 

 Thus Meek 1 described Sphaerium (?) idahoense Meek from Castle 

 Creek, collected by King. Gabb 2 described two species, Melania 

 taylori Gabb and LHhasia antiqua from a "Deposit on Snake River 

 on the road from Boise to the Owyhee mining country;" thus probably 

 from Walters Ferry. The same forms have been found, according 

 to Mr. George II. Eldridge, at Glenns Ferry, 120 miles above Walk- 

 ers Ferry. Dr. White describes the same two species and another, 

 Latia dallii, from a point 50 miles below Salmon Falls, Snake River, 

 which probably refers to Glenns Ferry, and states that these forms 

 differ considerably from any known fresh-water fauna of America 

 either fossil or living. 3 Both Meek and White are in favor of corre- 

 lating these Tertiary beds with King's Truckee Miocene. To this the 

 utterances of King are directly opposed, and it is, indeed, from 

 stratigraphic grounds, improbable that these beds are of Miocene 

 age. Near Glenns Ferry beds of sand and clay occur intercalated 

 between the basalt flows, and it is probable that the fossils came from 

 this locality and that all of them were collected in beds very closely 

 associated with the late basaltic eruptions, from which it would 

 follow that they should be placed in the latest Pliocene. 



Prof. O. C. Marsh states (oral communication, January, 1897) that 

 a large amount of Pliocene mammalian remains was found in a bluff 

 about 100 feet above the Snake River, some distance below Weiser, at 

 the old crossing of the stage road to Oregon, on the Oregon side of the 

 river. 



None of these localities were visited during the field season of 1896 

 on account of pressing economical and areal work in other sections ; 

 but from the area studied it was possible to read in its chief features 

 the later geologic history of the lower part of the Snake River basin. 

 The correlation of these results with the older work remains for the 

 future. 



TOPOGRAPHY. 



The chief topographic features of the region, of which the geology 

 is shown on PI. LXXX VII, are as follows : 



Broad flat mesas of basalt and Pliocene lake beds spread on both 

 sides of Snake River, though chiefly on the northern side. Through 

 these mesas the river has cut an abrupt canyon, bordered by basaltic 



1 Proc. Phila. Acad. Nat. Sci. 1870, p. 57. 



3 Paleontology of Gal., Vol. II, p. 13. 



' Proc. U. S. Nat. Mus. 1882, Vol. V, p. 99. 



