146 Scientific Intelligence 
The Introduction to the volume, after presenting sketches of the 
earlier explorations in the Upper Missouri region, describes the 
formations from which the fossils were collected, giving sections 
showing the thickness and order of superposition of the various 
subdivisions. The geographical extension of the same west of the 
Mississippi is also shown; and their relation to the subdivisions 
retaceous in Mississippi, Alabama, New Jersey, and in the 
Old World are fully discussed. The author also makes some re- 
marks on the mooted question in regard to the relation of the 
Lignites of the far-west to the Cretaceous and Tertiary systems, 
maintaining, as he had previously done, that these deposits belong 
in part to the Cretaceous and in part to the Tertiary: that is, that 
the beds at Coalville, Utah, and Bear River, Wyoming, are clearly 
Cretaceous, like those of Western Colorado; that those of Bitter 
reek, Wyoming, especially those below the horizon of the Hall- 
ville coal, are almost certainly Cretaceous; that those above, to 
the horizon of the Saurian bed at Black Butte Station inclusive, 
probably belong also to the Cretaceous, but may be Eocene; and 
t the Evanston and Carbon Station coal-bearing strata of 
ary. 
The Judith river fresh- and brackish-water beds of Montana, 
iti ica, i of Saurians 
: Eocene types 0 
and new species of shells that would be called Tertiary forms by 
almost any paleontologist (judging from their affinities), he 
thinks, may be Cretaceous, but he does not regard this conclusion 
e affinities and geological range, so far as known, of. each 
genus, are also fully discussed; and when represented by existing 
species, its habits and geographical distribution are generally 
stated, Most of the species, and some of the genera in the work, 
are here for the first time illustrated. 
y a few of the species are known to occur in the old world, 
and at localities in this country east of the Mississippi; and thesé 
are all from the Cretaceous, and show that the Niobrara and Fort 
Benton Groups, as well as perhaps the Dakota Group, represent the 
Lower or Gray Chalk, with possibly also the Upper Green Sanh 
