Reviezv of Recent Geological Literature. 193 
The number of specimens of aquatic or semi-aquatic mollusca from 
the loess in this collection, shown in a table at the end of the paper, is 
771, of which 750 belong to the pulmonale genus Limnaea. The 
great majority are L. humilis Say, which at present, is "quite as fre- 
quently found out of the water as in it," being "abundantly developed 
in ponds and streams which are dry during the greater part of the 
summer." 
There are 4,8 [6 specimens of fossil terrestrial molluscs in Prof. Shim- 
ek's. collection, of which 1,714 belong to three species of Succinea,- S. 
avara, S. lineata, and S. obliqua, which are often found at the present 
time in high and very dry situations. The temperature and rainfall of 
the region during the deposition of the loess must have been nearly as 
now, permitting the growth of abundant plant-food for these herbivorous 
land molluscs. The author therefore writes: "Summing up the evidence 
of the fossils, we may assert that it points to conditions not unlike those 
which exist to-day, and that geologists, in seeking for the cause and 
manner of the deposition of the loess, must give up the assumption of 
widely submerged areas over which fossiliferous loess now occurs, and 
of a cold climate." 
Although direct consideration of the mode of formation of the loess 
is not taken up by the author, further than the statement that its 
materials originated largely or wholly in drift, he apparently holds the 
same view as Udden and Sardeson, that the loess is chiefly of land depo- 
sition by wind action. While this seems to the reviewer a good expla- 
nation of the derivation of the loess upon many tracts, including those 
high above the valleys and plains, a much greater part of the loess, 
spread continuously along the broad avenues of drainage from the melt- 
ing ice-sheet in its recession from its lowan readvance, seems to be re- 
ferable to fluvial or sometimes lacustrine deposition, as shown by Cham- 
berlin in his discussion of the partly aeolion origin of this formation. 
With the depression of the glaciated area from its former high alti- 
tude, to which the snowy climate producing the ice-sheet appears to 
have been due, there was doubtless restored on the land bordering the 
ice nearly as genial climatic conditions as are nf)w enjoved by the same 
areas. The reviewer thinks that great floods from the ice-melting then 
filled the valleys and spread over wide flood-plains during a few weeks 
of each summer, and that these plains, covered thinly each season with 
new loess of such aqueous deposition, were clothed through each autumn 
and spring with vegetation, affording favorable conditions for the land 
molluscs whose shells are the predominant fossils of the loess. w. l'. 
Maryland Geological Survey, Vol. II, i8q8. Wm. Bullock Clark, 
State Geologist. 
The second volume of the Maryland Geological Survey admirably 
meets the expectations aroused by the first report from that survey. 
There is the same standard of excellence in the typographical work, 
in the illustrations and in the general appearance of the volume, while 
the 500 pages of text contain additional information of manifest prac- 
tical value. More thorough and complete discussion of certain of 
