REVIEWS 379 
Geology and Mineral Resources of the Sit. Louis Quadrangle, Missouri- 
Illinois. By N. M. FENNEMAN. U.S. Geol. Survey Bull. 438. 
LOE eps 7326 10. Tels. 0. 
This region is one of Mississippian and Pennsylvanian formations, 
overlain by Lafayette gravels, Pleistocene glacial tills and loess, and 
recent alluvium. In the drilling of deep wells, the logs of which are 
given, Ordovician and Cambrian formations are shown to be present 
beneath the Mississippian strata. The Paleozoic formations have a 
slight dip toward the northeast. 
Of economic importance are the Cheltenham fire clays, shales, and 
brick clays. One large Portland cement plant is in operation. The 
No. 6 coal of the Illinois reports has its western limit on the Illinois side 
of this quadrangle and is there mined. 
EX 1B 18 
‘“A Revision of Several Genera of Gymnospermous Plants from the 
Potomac Group in Maryland and Virginia.” By Epwarp W. 
Berry. Proc. U.S. Nat. Mus., XL (1911), 289-318. 
This revision is a simplification, combining many previously segre- 
gated forms. The genera considered are: Sphenolepis, Arthrotaxopsis, 
Cephalotaxopsis, Widdringtonites, Brachyphyllum, Sequoia, Abietites, 
and Pinus. 
Ne Bie 1B 
Glacial Erosion in the San Juan Mountains, Colorado. By ‘THOMAS 
CRAMER Hopkins. Proc. Wyo. Hist. and Geol. Soc., XI, 
pp. 14; pls. 8. 
In this well-illustrated paper evidence is cited against the idea, held 
by some geologists, that the theory of ice erosion is a fallacy. 
AN 18a e) ae 
