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volume. Each rock type is treated rather fully as to origin, varieties, 

 alteration, and surface expression. The current conceptions of the 

 different rock-forming processes are developed historically, the most 

 important contributory theories, past and present, being discussed in 

 each case. It might be said that this is done too fully for an elementary 

 book; but, on the other hand, the critical background which this presenta- 

 tion gives the reader is valuable, and will make the book of interest to 

 many geologists. 



The extensive illustrations used to bring out different points are 

 interesting and effective, and are chiefly drawn from Europe and other 

 parts of the Eastern Hemisphere, thus being fresh to many Americans. 



T. B. R. 



