64 The American Geologist, January, isov 
Tlu> Eocene De))()sifn of the Middle Athintie Slop? in DelatV(n-e, Mary- 
land and Virginia. By William Bullock Clark. (U. S. Geol. Sur- 
vey, Bull. Ul, 1G7 pp., 40 pis., 4836.) The Eocene strata (Pamunkey 
formation of Darton) of the Middle Atlantic slope form a distinct unit, 
being s?parated from the Cretaceou.s below and from the Miocene above 
by erosion intervals. In lichologic character these deposits are essen- 
tially glauconitic, and they contain a considerable fauna, although the 
state of preservation of the fossils has heretofore caused a large number 
of the Eocene forms to ha overlooked. The strata strike north and 
south, or northeast and southwest in the northern part of the area, and 
the dip is toward the east or southeast, averaging twelve and one-half 
feet per mile. The average thickness is about 200 feet, although in 
places the beds attain a thickness of 300 feet. From the Potomac River 
section, which is the best and most characteristic section exposed, the 
author has been able to establish two clearly delined paleontologic 
stages, — a lower or Aquia Creek stage, and an up^jer or Woodstock 
stage, — but it is not po.ssible to recognize over the whole area minute 
paleontologic or lithologic divisions. 
In discussing the correlation of the Middle Atlantic Slope Eocene 
with the Gulf Eocene Prof. Clark calls attention to the diverse views on 
this subject and also to the different conditions under which the depos- 
its were laid down. In the former region the strata were accumulated 
slowly at some distance from the shore and along a coast which received 
no large rivers, while in the latter region the accumulation was rapid 
and more extensive and was largely influenced by the debris brought 
down by large rivers. The author concludes that the Middle Atlantic 
Slope Eocene is the equivalent in a broad way of most of the Gulf series, 
except that the upper part of this series is probably lacking in the re- 
gion he is discussing. The Aquia Cx-eek stage is broadly the equivalent 
of the Lignitic, and the Woodstock of the Claiborne. 
The work contains a bibliography of the subject, a historical review 
of investigations, a brief outline of Coastal Plain history, a discussion 
of criteria of correlation, and descriptions of the fauna, which is illus- 
trated by thirty-six plates. u. s. g. 
Tlie Cambrian Rocks of Pennsylvania. By Charles D. Walcott. 
Bulletin 434, U. S. Geol. Survey ; 43 pages, with 45 plates; 4896. This 
paper gives the results of field work in 4892 and 4893. The discovery of 
the Olenellus or Lower Cambrian fauna in the Reading sandstone sup- 
plies the completing link in the correlation of the basal quartzites of the 
Cambrian series along their entire extent from Vermont to Tennessee. 
Much further work is needed for determination of the division between 
the Cambrian and Ordovician series in this region. Intraformational 
conglomerates, in thin bands, are described as observed in many locali- 
ties. Their origin is ascribeti to tidal action on gently sloping shores or 
on the flats of estuaries, hardened layers due to drying when exposed 
by the ebb of the tide having been broken up by the incoming tide. 
w. u. 
