104 Review of Hall and Whitney’s Geology of Iowa. 
Crinoids for description and illustration. Even the Permian has 
some representative beds, though discovered too recently—the 
Introduction states, after the Permian fossils of Kansas had 
known—to be described in detail in this volume, — 
Prof. J. D. Whitne contributes chapters on the Physical 
Economical Geology, and the eighth to the Palsontology, the 
whole work being comprised in 724 pages, with 29 steel - 
In Chapter I, we have a concise view of the topography of lows. 
The State is a vast plain, gradually rising as we proceed from 
the east towards the west, and from the south, sonh : 
absolute elevations are given from the railroad surveys, when 
such could be obtained. In this plain the streams have cut deep 
and narrow valleys, which are bordered by precipitous “ lulls, 
as they are termed, the river-bottom, bluff and prairie being the 
three ga eres features of the topography of the State. + 
height and steepness of the bluffs decrease gradually from the 
north towards the south. The course of the tributaries of the 
two great rivers forming the eastern and western boundaries of . 
State, the Mississippi and Missouri, is adduced as evidence 
the direction of the drainage having been determined by yee 
sets of low and narrow flexures of the strata, one set running 4 
a northwest and southeast direction and the other nearly ab ba 
250 miles and draining a valley which is only from eight 
twelve miles in width. The “mounds” which break the 
ony of the landscape in the lead region, are described as outhies ‘ 
of Niagara limestone, overlying strata of the Hudson river gt0"Fr 
and rising in isolated, flat-topped hills, presenting evident 
extensive denundation. These mounds are from 400 to OW ™ 
above the Mississippi river, and about 200 above the genet 
evel of the prairie at their bases. 
