1893.] Recent Literature. 985 
RECENT LITERATURE. 
Iowa Geological Survey.'— The first annual report of the Iowa 
Geological Survey just issued is unusually attractive in appearance, 
and presents an interesting array of papers. That by Professor Calvin 
deals with some phases, of the, as yet, imperfectly known Cretaceous 
deposits occurring in Woodbury and Plymouth counties, and contributes 
important information concerning them. These deposits in the area 
studied consist of soft sandstone interstratified with bands of ferruginous 
nodules and variegated, often parti-colored, clays, overlaid by white, or 
yellowish chalk, in part indurated into beds of soft fissile limestone. 
White, in his report of 1870, termed this chalk the Inoceramus bed, 
from the great numbers of Inoceramus problematicus found in it, while 
the lower beds were called the Woodbury sandstone and shales. Pro- 
fessor Calvin, mainly on paleontological evidence, separates the latter 
into two divisions, the lower of which, chiefly sandstones containing 
impressions of leaves belonging to species of plants resembling our 
modern forest trees and with animal remains exceedingly scarce, he 
correlates with the Dakota group of Meek and Hayden. The second 
division, principally shales containing impressions of valves of marine 
molluscs associated with the vertebrse of bony fishes and the skeletons 
of marine saurians, is the Fort Benton group of the same authors, 
while the chalk represents their Niobrara group. The few molluscan 
remains found in the beds of the Dakota {group are related to brackish 
water species and imply that the beds were laid down in an estuary, or 
at least in a region where the sea was shallow and large volumes of 
fresh water were poured into it. 
The beds of the second division show a gradual duns in the con- 
ditions of deposition owing to the deepening of the sea and the shift- 
ing of shore line farther east. True marine molluscs, and fishes and 
reptiles occupied the region, and left their skeletons to be buried in the 
finer mud that characterized the deposits then slowly accumulating in 
the open sea. 
During the succeeding epoch where the chalk and shell-bearing lime- 
stones were forming, the water, by subsidence of the ocean bed, had 
become deeper, and the shore-line of the Cretaceous sea attained its 
farthest extension eastward probably reaching as far as the Mississippi 
! First Annual Report for 1892, with Accompanying Papers. 8vo. 472 pp. with 
ten plates and twenty-six figures. Samuel Calvin, State Geologist, Des Moines, 1893. 
