REVIEWS 189 
brown olivine, and colorless tourmaline could not be found under the 
proper divisions. These minerals, with the colors given, are, to be 
sure, more or less rare. The tables appear to be excellent for at least 
the more common varieties of minerals. 
The volume also has chapters on the physical and chemical properties 
of minerals, the polarizing microscope, the formation and occurrence of 
minerals, qualitative blowpipe methods, gems and precious stones, as 
well as a classification of minerals according to the elements they con- 
tain, giving their uses and statistics of their production. Six pages are 
devoted to a glossary. 
Perhaps one of the most noticeable defects of the book is its entire 
lack of references, whether in the form of a general bibliography or as 
footnotes. There are a number of typographical errors, though but few 
that might lead to confusion were noticed. There are some other errors, 
not so surely typographical, such as placing wulfenite under the wol- 
framite group, giving tourmaline the formula H..B.Si,O., and placing 
the origin of the minerals in igneous rocks under minerals formed from 
fusion (rather than from solution). The chemical distinction between 
the different plagioclase feldspars is poor. 
In spite of these minor defects the work is excellent, well arranged, 
and attractively presented. 
IDs Neda: 
Geology and Mineral Resources of the Hennepin and La Salle Quad- 
rangles. By GILBERT H. Capy. [Illinois Geological Survey, 
Bull. No. 37. Urbana, 1919. 
The area represents one of the richest agricultural, manufacturing, 
and mining communities in the Middle West, including parts of La Salle, 
Bureau, and Putnam counties of north-central Illinois. The manufactur- 
ing wealth is dependent to no small degree upon the natural resources 
of the region. 
General geology—tThe area forms a part of the Glaciated Plains 
Province, the larger part of it being monotonously level, what relief 
there is being chiefly due to glacial drift. Stratigraphically the rocks 
of the region range from Cambrian through the Carboniferous, with 
Pleistocene glacial drift. Good detailed sections and faunal lists are 
given. There are several important unconformities. Though the strata 
are for the most part nearly horizontal, the La Salle anticline, or, as the 
author suggests, more properly the La Salle monocline, shows dips up 
to 50° locally. 
