1492 Cincinnati Society of Natural History. 
Cretaceous, and to bind the Eocene, the Miocene and Pliocene with 
the present as one connected age. ‘The lower Eocene lake deposits are 
found superimposed conformably upon the brackish deposits of the 
Fort Union Group. The Eocene is divided in ascending order, into 
the Wasatch, Green river and Bridger Groups, though these are found 
conformable with each other in some places and mark a continuing age. 
The Wasatch is again divided by having the lower marls called the 
Puerco Group, and the Green River Group is divided, for convenience, 
in some places, into an upper and lower Green River Group. It would 
seem that all other names proposed for the fresh-water Eocene deposits 
are synonyms, though the equivalency of strata has not, probably, in 
all cases; been determined. ‘The Miocene is known in the lower part 
as the Wind River Group, and higher as the White River Group, and 
sometimes the latter name is used to the exclusion of the former. In 
some places the upper Miocene is called the Truckee Group. The 
Brown’s Park Group, Sweetwater Group and Monument Creek Group 
are Miocene, but their exact position is not so fully determined, The 
two latter are supposed to be equivalent to part of the White River 
Group, and the former may be so too. The Pliocene is very properly 
called the Loup Fork Group. It has also, in part, received the name 
of the Salt Lake Group, and a conglomerate of the age of the upper 
part of the Pliocene is called the Wyoming Conglomerate. The dis- 
tribution of these Groups and questions of synonymy, have been con- 
sidered at some length, in preceding pages, and in the near future 
the nomenclature will no doubt be more definitely established. 
The northern drift does not occur in California, nor on the Pacific 
coast as far north as British Columbia and Alaska. There are no in- 
dications throughout the Rocky mountain region of any general ice 
action. ‘There are no such exhibitions of scratched and grooved rocks 
succeeded by fossiliferous marine clays and sands with bowlders, as 
occur in the New England States and St. Lawrence region, nor of 
scratched rocks and ancient soils succeeded by clay, sand and gravel 
with bowlders, as occur in the central part of the continent; but, on the 
contrary, the whole region may be regarded as an absolutely driftless 
area, except as to local drift produced upon the shores of the Tertiary 
lakes, and more or less distributed by the rivers, that in the course of 
time cut out the canons which drained them. On the borders of the ancient 
lakes, on the borders of the ancient lake-like expansions of the rivers, 
and on the borders of the ancient rivers, there are terraces which mark 
old shore lines at various places from Mexico to Alaska, and especially 
