Review of Recent Geological. Literature. 399 
teen of the principal published Cretacous sections of this continent 
and afford at the same time a view of the author's correlations. In 
each table or section the twenty-six letters of the alphabet, equally 
spaced, stand for the whole duration of Lower Cretaceous and again in 
like manner of Upper Cretaceous time. Thus the supposed relative 
lengths and equivalency of the local formations of each region are very 
definitely stated. On the map of known Cretaceous areas the North 
Interior region should be extended eastward from North and South 
Dakota to cover likewise continuously, although less deeply, consider- 
able tracts of western Minnesota and northwestern Iowa. Biblio- 
graphic references, with brief annotations, occupy 35 pages, followed 
by a concise historical sketch of the progress of discovery and explora- 
tion of our Cretaceous areas. 
Correlation Papas. Eocene. By William Bullock Clark, pp. 
173, with two maps. (Bulletin No. 83, U. S. Geol. Survey, 1891. Price 
15 cents.) In the Atlantic and Gulf coast region the separation be- 
tween the Cretaceous and Eocene is determined with a general concur- 
rence of opinion among geologists, as shown in this report; and the later 
Tertiary or Neocene is found unconformably overlying the Eocene, with 
fossils that readily distinguish the two horizons. The Eocene there is 
wholly marine and is more or less clearly assigned to three horizons, 
lower, middle, and upper. On the Pacific coast two very distinct divis- 
ions are recognized, namely, the Tejon group, of marine origin, repre- 
sented in California, Oregon, and Washington; and the brackish Puget 
group, found in Washington alone. Lacustrine Eocene beds cover 
broad continuous tracts on the eastern and western flanks of the Rocky 
mountains, and are scattered in smaller basins from Colorado to Nevada 
and from Montana to Texas. Here the system comprises the follow- 
ing members in ascending order, as correlated by Dr. Clark: the upper 
portion of the Laramie group, the Arapaho, Denver and Puerco beds, 
and the Wasatch group, belonging to the Lower Eocene; the Manti 
and Amyzon beds, and the Wind River and Green River groups, all re- 
garded as co-extensive, or nearly so, with the middle epoch of this 
period; and the Huerfano beds, and the Bridge r and Uinta groups, 
forming the third and upper part of the series. For each of the three 
chief regions of our Eocene formations, near the eastern and western 
coasts, and in the Cordilleran mountain belt and adjacent plains, a de- 
tailed historical sketch is given, with plentiful citations of the publica- 
tions relating to them; and the same and other works are also noted in 
a final bibliography of 12 pages. Like each of the preceding and fol- 
lowing correlation papers, this essay has a good index, permitting '|iiick 
reference to its contents and making it a most convenient and valuable 
handbook in field work and research. 
Correlation I'lipern, Neocene. By William Hkai.kv Dai. Land GIL- 
BERT Dennison Harris, pp. 349, with three maps and 4:'. tigures of 
sections and profiles in the text. (Bulletin No. s l. V. S. Geol. Survey, 
1892. Price 25 cents.) The junior author, Mr. Harris.examined the lit 
