Review of Recent Geological Literature. 399 
up as dunes and spread as surface sheets, after a few years, a 
stratum as thick as, and constituted like, that of the Missouri- 
Mississippi valley. Given such a wind over the same region, 
periodically, under the same parched condition of the surface, 
it would only require an expanse of water in which this dust 
could settle, to form a loess clay, or loam. With the accom¬ 
panying and following rains other particles would be washed 
down from the lands, mingling with some strata of sand, or of 
gravel, and a transition from loess to drift sand would be 
built up such as has been described in several places. 
REVIEW OF RECENT GEOLOGICAL LITERATURE. 
Marine shells and fragments of shells in the till near Boston. By War + 
ren Upham. (From the proceedings of the Boston Society of Natural 
History, yol. xxiv; also in Am. Jour. Sci., May, 1889.) The remark¬ 
able oval accumulations of till called lenticular hills or drumlins are 
found to contain in Winthrop, the islands of Boston harbor, and on 
the peninsula of Nantasket, many fragments of marine shells, of which 
about twenty species are identified, all of which are now living in 
Massachusetts bay. These shell fragments occur in the unstratified 
glacial drift or till, in the same manner as its boulders and rock frag¬ 
ments; and Mr. Upham concludes that they were derived from the 
glacial erosion of marine deposits of interglacial age within a few miles 
northwest, from which direction the drift has been brought. None 
have been found fartherjnland, and it is thence inferred that the rela¬ 
tive heights of land and sea there during the principal interglacial 
epoch were nearly the same as now. Venus mercenaries L., the round 
clam or quohog, is the most abundant species; and it is regarded as 
evidence that the sea on that part of the coast became warmer in the 
interglacial epoch than at the present time, for this species is now 
scarce in Massachusetts bay, but it is plentiful south of Cape Cod, 
with southward range to Florida. 
Seventh Annual Report of the United States Geological Survey to the 
Secretary of the Interior, 1885-’86. By J. W. Powell, Director. Wash¬ 
ington, Government Printing Office, 1888. pp. xx and 656; plates 
lxxi: figures 114. 
This valuable report, bearing date Oct. 1, 1886, has only been re¬ 
cently issued from the press and bindery, and was distributed to the 
working geologists of the county about a month ago. 
The progress of the topographic surveys and engraving for a con - 
tour map of the United States, in charge of Mr. Henry Gannett, is very 
encouraging; though so vast a work must of course occupy many 
years. The scale for the greater part of the maps is 1:125,000, or very 
nearly two miles to an inch, with contour lines for each 100 feet; but 
considerable areas of the territories are mapped on the scale of 1: 250,- 
000, about four miles to an inch, with contours for each 200 or 250 feet. 
