DEVONIAN FAUNA. 71 



posited being relatively small. Paleontology fails equally with geology to 

 point out any strong reasons for subdivisions ; moreover, it would be impos- 

 sible, from our present knowledge, to subdivide the epoch into horizons as 

 recognized in the Mississippi Valley and the Appalachians of the Atlantic 

 coast. The groupings of fossils at the base and those at the top show very 

 considerable difference in the fauna, but the mingling of species throughout 

 the beds has rendered it difficult to draw any line of separation. Many of 

 the species characteristic of a restricted horizon elsewhere have been identi- 

 fied in the Nevada limestone, but with a wide vertical range, and in some 

 instances have reversed their relative positions, as recognized in New York 

 state. At no distant day, when the epoch becomes still better known and 

 comparative studies have been made with other localities in the Great Basin, 

 it may be quite possible and even desirable that such divisions should be 

 drawn. At present, however, it will be quite sufficient to speak in general 

 terms of an upper and a lower horizon. 



The Nevada limestone has yielded an exceedingly rich and well preserved 

 fauna; certainly no epoch in the Great Basin can surpass it in general in- 

 terest, either in the variety of its organic forms, in the number of species 

 determined, or in the commingling of species found elsewhere in widely 

 separated localities. This terrane alone has yielded more species than the 

 Cambrian and Silurian periods together, and surpasses the entire Carbonif- 

 erous, with its great thickness and wide areas, by more than one hundred 

 specific forms. From Eureka and White Pine together it has furnished 

 over two hundred species, of which one-third have been described for the 

 first time in the report of Mr. C. D. Walcott; 1 while, a fact of great interest 

 as regards geographical distribution, one hundred and nineteen of them are 

 specifically identical with previously described forms from other well known 

 Devonian localities, and no less than seventy-nine of them have been identi- 

 fied with species occurring in New York. The Upper Helderberg, Hamil- 

 ton, and Chemung are all well represented so far as species are concerned, 

 although the vertical range of certain species by no means agrees with the 

 limits assigned to them in New York. In comparing the Nevada limestone 

 of the Great Basin with the Devonian of New York state, Mr. Walcott says: 



'Paleontology of the Eureka District, Monograph VIII. Washington, 1884. 



