216 QO. A. White—Jura-Trias of North America. 
of these works the contained fossils are fully illustrated and de- 
scribed, and the strata are, by those fossils, referred to the 
8 
fully explored by the survey in the latitude of 40°, and over a 
width east and west of nearly four degrees of longitude (117° 
to 121°) . . . . But sufficient paleontological evidence 
has been obtained to enable us to state that this formation ex- 
tends from Mexico to British Columbia, and that it occupies a 
vast area, although much broken up, interrupted by eruptive 
rocks, and covered in many places by heavy accumulations of 
volcanic materials.” 
o fossils, however, as already stated, or at least no inver- 
tebrates, were known to exist in any North American strata 
east of that region which could be confidently referred to the 
Triassic period, until the autumn of 1877, when a collection 
was brought in by one of the parties of the United States Geo- 
logical Survey of the Territories, in charge of Dr. F. V. Hayden, 
which was found to contain molluscan types that are p. ainly 
Triassic. The collection referred to was made by Dr. A. 0. 
Peale, field geologist, from two or three localities in southeastern 
Idaho, and i 
little or no question to the Jurassic period are well known; 
such, for example, as Pentacrinus asteriscus Meek and Hayden, 
Belemnites densus M. & H., Camptonectes bellistriatus M. & HL, 
Eumicrotis curta Hall, Ostrea strigilecula White, &e. Wherever 
in that region a collection of Jurassic (or as they have come to 
be commonly designated, Jura-Trias) fossils has been made, 
some one or more of these species has generally been found 
among them; and the new forms, whenever they have beet 
discovered, have not generally been in excess of those which 
were previously known, thus suggesting the discovery of n0 
separate horizons. Almost the contrary, however, is the case 
with the collection from the localities here referred to in south- 
eastern Idaho, because, out of the list of the species obtained 
there and presently to be mentioned, only three were prev! 
ously known, and only one (Eumicrotis curta) has ever been 
found associated with well-known Jurassic fossils. : 
At the principal one of these localities, which is about sixty- 
five miles north of the southern, and eighteen miles west of the 
eastern, boundary of Idaho, Dr. Peale found the Jura-T'as 
