378 The American Geologist. December, i904. 
thus be affiliated with the system with a northwesterly trend. Mr. von 
Drasche, however, calls attention to the fact that the Sierra Zambales 
exhibits a remarkable double repetition of the two main directions of 
Luzon, one northerly, the other northwesterly. With Arayat I can do 
no better than leave it in its impressive loneliness." 
The latest information regarding the outer groups of the 
Malayan archipelago is contained in Koto's paper, already cited. 
In his geomorphologic studies von. Richthofen has included a 
general and, except that Japan is not included, a summary 
paper especially devoted to the genesis of the island arcs.* He 
ascribes the dislocation planes represented in the arcs 
to the operation of tension, as has already been par- 
tially explained in an earlier review of this series. This theory 
advanced in the studies to the present writer appears less 
satisfactory than the descriptive portions which have been al- 
ready reviewed, and on this account is left without further com- 
ment to the reader. Tlie paper is of especial interest to an 
American reader for the reason that it presents the views of 
this great geographer and illustrates by examples the terms 
which have gradually come into use by the Austrian and Ger- 
man schools to describe the composition of mountain systems. 
University of Wisconsin, 
Madison, Wis. 
A THEORY OF ORIGIN FOR THE MICHIGAN 
GYPSUM DEPOSITS.! 
By G. P. Grimslky, Morgantown, W. Va. 
The most generally accepted theory of origin of the large 
deposits of gypsum and salt, has been the evaporation of salt 
water lakes, bays, and seas, cut off from the main ocean. This 
theory has been given for the Iowa, New York, and Kansas 
deposits in the reports on salt and gypsum in those states. In 
the Kansas report, the writer endeavored to picture the his- 
tory of the changes resulting in the deposition ot gypsum in a 
bay whose waters retreated to the southwest in Permian time. 
• Voa Richthofeu: Geomorphologischc Studien aas Ostasicn. IV. Uber 
Gcbirgskettungen in Ostasien, mit Ausschluss yon Japan. SitzungMber. d. k> 
pr. Akad. d. Wiss., vol. 38, 1903, pp. 867-891. 
+ Published by permission of the Director, ^Michigan Geological Survey. 
