200 REVIEWS 
III. CAMBRIAN 
The eruptives of the Manitou series gradually cease and give place 
to whiter and more siliceous sandstones, which in turn give way with- 
out any general break to the magnesian and argillaceous limestones of 
the Upper Cambrian. These Upper Cambrian rocks are of compara- 
tively slight extent and importance in the area covered by the report. 
Igneous rocks—The igneous rocks, both acid and basic, of the 
Archean and Taconic are regarded as originating from the hydrother- 
mal fusion of the older rocks, mostly from the clastics. The interme- 
diate stages may often be seen. 
The igneous rocks are of three classes— granites, diabases, and 
quartz-porphyries. The granites are of three relative ages, two being 
Archean and the third Taconic. ‘They are referred to the fused por- 
tions of a still earlier acid clastic. The diabases are also of three 
relative dates, in this case one being in the Archean and two in the 
Taconic. They are believed to have been derived from the lowest green- 
stones, or to occur as apophyses of the gabbro, itself a secondary condi- 
tion of the greenstone. The quartz-porphyry dikes are again of three 
periods, one each in the Lower and Upper Kewatin, and one cutting 
portions of the Taconic. They are supposed to have been derived 
from the great quartz-porphyry mass of the Lower Kewatin, or from 
some later clastic. 
Glacial Geology.— Besides the mass of observations relating to the 
crystalline rocks, there are a considerable number relating to the 
glacial geology of the northern portion of the state, but these observa- 
tions are not systematically discussed with reference to the great 
problems of glacial geology. 
The thirty or more maps included in the report give, in addition 
to the geology and ordinary topographic features, approximate con- 
tours for every fifty feet, which adds greatly to their usefulness and value. 
The maps are pleasingly colored and neatly executed. The volume is 
profusely illustrated by photographic reproductions and line cuts. 
The former, especially, are numerous, and though not always what 
might be desired in the point of clearness and appropriateness, add 
materially to the attractiveness and value of the report. 
As one reads the report he cannot but be impressed by the great 
number of observations made and the mass of facts accumulated, but 
the disconnected and unsystematic manner of presentation, which 
necessarily follows from the geographical treatment adhered to 
