O. Fisher— Physics of the Earth's Crust. 287 
judgment upon it. The discussion cannot be briefly summa- 
rized. 
derives from his construction a mechanism for volcanic action, 
but since it is impossible to abstract his view and do it justice, 
the reader must be referred to the work itself. 
If we may venture to sum up in a very few sentences the 
general tenor of this book we should say that its earlier and 
middle chapters show that interior contraction cannot 1e 
source or origin of the earth’s physical features. Nevertheless 
once by elastic vapors would, he thinks, supply the requisite 
machinery not only of compression but also of volcanic action. 
In this work Mr. Fisher has rendered extremely valuable 
Service to the science of physical geology, and chiefly to that 
branch which deals with its largest and noblest problems. My 
Own thoughts have for some years run so much in the same 
paths, that it would be most pleasant to speak at considerable 
length upon many points he has discussed, but I can advert to 
only a few of them. First and foremost he has rendered most 
cause of interior contraction; for contraction is, they think, 
absolutely necessary to explain the physical features of the 
earth. Mr. Fisher has touched—all too briefly it seems to 
me—upon an argument quite as fatal to this modified form 
of the theory, as the one he has so fully elaborated, and 
v 
indeed, of a more direct and comprehensive character. For 
