62 Scientific Intelligence. 
to supplement and extend the account by Prof. Whitney, adding 
the results afforded by the more recent mining operations and a 
further study of the regions. 
e Atlas consists of a series of colored plates, illustrating in 
sections the geology of the State; and others for eastern Wi 
think, for the small amount of detail in the geology. 
e cite from the volume the following facts and conclusions 
relating to the Wisconsin drift. 
In the first place the facts with regard to the driftless region, 
which covers Southwestern Wisconsin and the borders of Minne- 
st ‘ 
and Iowa adjoining, described a d rof. J. D. 
Whitney, are brought out with additional observations; and th 
view of Dr, Percival, its first describer, an f. itney is sus- 
southeast town of Minnesota—that of Houston. The former 
absence of the ice is proved by the absence of gravel and stones, 
which suddenly cease on entering the region, and, as Prof. Irvin 
states, by the character of the hills and ravines and the existence 
over it of numerous fragile sandstone peaks. The origin of this 
2 
? . 
latter brings out, in his report, a new theory in explanation of it. 
According to the observations of Prof. Irving, in connection 
h 
h 
west (3) along a Keweenaw Bay depression, west of southwest 
: depression, as a ; 
reached to Illinois. While those of the Keweenaw Bay depres 
sion and Western Lake Superior continued westward and south- 
