410 



THE AMERICAN NATURALIST 



[Vol. XLI 



111 tlio order indicated. A hnal chapter in this part ot the book dis- 

 cusses off-sliore and deep-sea deposits. Under the heading "Internal 

 deological Agencies" the following chapters appear: Movements 

 ot the Earth's Crust, Earthquakes, Volcanoes, Underground Struc- 

 tures of Igneous Origin, Metamorphism and Mineral Veins. Histori- 

 cal Geology is treated in the usual manner, the principal systems and 

 some of their characteristic fossils being described in order, beginning 

 with the Pre-Cambrian. Special emphasis is laid upon the evolution 

 ot the North American continent and the evolution of life upon the 

 planet. 



It is probable that manv will doubt the wisdom ot dropping out 

 structural geologv as a special subject and treating it onlv m connec- 

 tion with geological processes. There are difhculties in the way of 

 such a treatment, one being the danger that the elementary student 

 will not discriminate sufhcientlv between the process, the structures 

 diu to tht j)rocess, and tht tructures which mereh afiect the operation 

 of the process, all of which are treated under a single tit e. In the 



different tactors involved, although in places a stronger (liscnininatioii 



