i56 The American Naturalist. [February, 
ln an article of 52 pages on the optical recognition and economic 
importance of the common minerals found in building stones, Luquer” 
mentions the principal microscopic characteristics of the most import- 
ant minerals with sufficient fullness to enable the technical student to 
determine them inthe thin section. He also notes the effect of pres- 
ence of each upon the value of the various building stones in which 
they occur. He, moreover, describes the usual associates of each dif- 
ferent mineral, and so incidentally gives the composition of the prin- 
cipal rocks used in constructions. The article in pamphlet form is 
simple and useful. 
1 School of Mines Quart. xv, p. 285-336. 
