966 THE AMERICAN NATURALIST. (VoL. XXXII. 
values are fully illustrated. This last-mentioned feature of the vol- 
ume will be enthusiastically received by English-speaking teachers of 
mineralogy, since it embodies descriptions of methods heretofore 
available only in foreign text-books. 
The descriptive part of the volume is essentially an abridgment of 
the sixth edition of Dana’s System of Mineralogy. 
Two excellent indices close the book. One is a general index, or 
index of topics, and the other an index to the mineral species dis- 
cussed. The two occupy about twenty-two pages. 
The volume constitutes an excellent introduction to modern min- 
eralogy. It fills a want long felt by teachers who realize that the 
study of minerals is much more than a mere description of chemical 
compounds. This has long been understood on the continent of 
Europe, where the best mineralogical text-books have heretofore 
been published, and now, we are glad to say, it is being rapidly 
accepted as a truth in America; a fact due largely to the interest 
taken by American students in petrographical investigations. Pro- 
fessor Dana’s text-book is the equal of any foreign text-book, either 
as a student’s handbook of descriptive mineralogy or as an intro- 
duction to special works in petrography. 
It is unnecessary to state that the treatment of all branches of the 
subject is accurate and as full as is desirable, since the author’s 
name is a guarantee that the work is well done. , W. S. B. 
Michigan Volcanics. — Clements? decribes a series of intrusive 
rocks from the Crystal Falls iron district in Michigan which he 
believes to be genetically connected. Embraced in the series are 
diorites, gabbros, norites, and peridotites. The diorites are inter- 
mediate in acidity. They vary in texture between granitic, ophitic, 
and micropegmatitic. Their plagioclase is andesine, but in addition 
to this feldspar they contain also considerable quantities of ortho- 
clase. This mineral and quartz form the mesostasis. Brown and 
green hornblende are both present, the latter surrounding nuclei of 
‘theformer. Both are regarded as primary. The mineralogical varie- 
ties of the rock recognized are : quartz-diorite, tonalite, quartz-mica- 
diorite, and mica-diorite. By the subordination of the plagioclase 
and an increase in the proportions of orthoclase and quartz present, 
the diorites pass into granites, 
The gabbros and norites, like the diorites, contain more or less 
orthoclase and a large quantity of hornblende. This latter mineral 
1 Journ. of Geol., vol. vi (1898), p. 372 - 
