442 REVIEWS 
when the latter are present as a sulphate. The process is welt founded 
on known principles, and the phenomena accounted for are among the 
most common and heretofore most puzzling encountered in mining. 
The solving of this difficulty is likely to be of the highest practical 
utility. 
Mr. Lindgren’s paper on metasomatic processes gives sharp defini- 
tion to many heretofore hazy phenomena and will be of considerable 
utility both in the development of theory and practice. | 
In general, the volume is notable in that for the first time the 
results of recent investigations in physical chemistry are applied to the 
solution of the problems of ore genesis. The results attained are most 
promising, and open up enticing vistas of what may be expected from 
further investigations along these lines. For example, the question 
may be asked whether, in seeking an explanation of the chemical 
problems involved, we have not relied too exclusively upon the influ- 
ences of heat and pressure. If we keep in mind the very large place 
in the field of research which the diminutive ion now holds, and the 
close relations obtaining between ions and electric forces, one may 
well question whether here is not a fruitful field for investigation. 
The startling results already obtained in physiological investigations 
by studying the operation and effects of the electro-motive force hint 
at perhaps equally important results awaiting the investigator in other 
fields. 
H. Foster BaIn. 
IDAHO SPRINGS, COLO. 
SUMMARIES (OF GHEE Ei RE RALU REO S ERUCG TU ReAIE 
NACHIS IRATE Senne 
EDWIN C. ECKEL. 
UNDER this heading the writer purposes to summarize at intervals the 
literature relating to the economic geology of building stone, road materials, 
cements, lime, gypsum, clays, etc. Except when the word “comment” 
expressly appears, the matter presented will be simply a summary of the 
statements and opinions appearing in the paper under discussion. The writer 
will endeavor to indicate briefly the scope of each paper, following this by a 
résumé of the ovzgina/7 matter contained in it. 
Bascock, E, J. Clays of Economic Value (tn North Dakota). First Report 
North Dakota Geol. Surv. Pp. 27-55, 3 plates, Igol1. 
The clays of North Dakota are derived from the Pleistocene, the Laramie, and 
the Fort Pierre division of the Cretaceous. The Pleistocene clays include the yellow 
