Geology and Mineralogy. 399 
t f 
described; first the determination of the specific gravity, then 
d 
Tg 
amount of useful information which will be hardly found else- 
where in so convenient a form. 
Il. Grotoagy AND MINERALOGY. 
WatTsr P. . 
U.S. Geogr. and Geol. Survey of the Rocky Mountain Region, J. 
W. Powell in charge. 566 pp. 4to, with an atlas folio, 18 plates, 
sum with some impure limestone referred provisionally to the 
Triassic, the Jurassic, Cretaceous,’ A large number of fossils 
ste 
135 pages of the volume, and their illustrations 16 of the plates. 
The results show that the horizon of the Primordial beds is about 
the same with that of .Wisconsin; that the Subcarboniferous and 
Permian groups could not be identified, while the Carboniferous 
is well represented by its mollusks and coais; that the Jurassic 
beds are full of fossils, as first made known by Hayden’s survey in 
