REVIEWS 197 
warping of the surface. The streams again began to adjust themselves 
to their new conditions, a work in which they are still engaged. 
Hayes has made out the following changes which the streams have 
gone through in reaching their present courses. First, they moved 
westward to the interior sea as antecedent streams during the first cycle. 
Then they were diverted southward to consequent courses, and at last 
flowed westward as subsequent streams. 
The way in which peneplains are correlated forms an interesting 
section of the paper. ‘The types of stream basins as found in the region 
are vividly described. ‘The maps, of which there are five, repay care- 
ful study. 
lay els tale (Ce 
Geology of Minnesota, Final Report, Vol. IV. By N. H. WINcHELL, 
U.S. Grant, WARREN UpHam, and H. V. WINCHELL. Quarto, 
pp. i-xx, 1-630, with 31 geological maps, 48 photographic 
plates, and 114 figures. St. Paul, 1899. 
This volume, which completes the areal geology of the state, follows 
its predecessors in the geographic arrangement of the subject-matter. 
The area covered embraces the northern third of the state, and includes 
some thirty counties and districts. The bed rock of the region, with 
the exception of scattered patches of Cretaceous, is almost universally 
crystalline in character, and is referred to the Archean and Taconic. 
The thickness of the drift is very great throughout most of the region 
considered, several counties in the northwestern part of the state pre- 
senting no outcrops whatever of the bed rock. 
The crystalline rocks in this largely new field have naturally 
received much attention, resulting in the accumulation of a consider- 
able mass of new facts relating to the Archean and Taconic, especially the 
former. The interpretations based upon these facts differ considerably 
from the commonly accepted views as to the character and divisions of 
the ancient crystalline rocks, and especially as to the assumed repre- 
sentative of the original crust of the earth. 
It is to be regretted that the first presentation of a new classifica- 
tion should be somewhat lacking in clearness, but nowhere in the 
volume is there a satisfactory statement of the divisions into which 
the various clastic and igneous rocks of the state have been separated, 
nor of the equivalents in the ordinary classifications. As nearly as 
