390 . The American Geologist. December, 1904. 
-.flow and of the development of such secondary structures as slatiness, 
schistosity, and the gneissosdty are offered. -.Perhaps the most important 
■generalization is, that "Rock flow is mainly accomplished through con- 
tinuous solution and deposition, that is, by recrystallization of the 
rocks through the agency of the contained water. But rock flow is 
partly accomplished by direct mechanical strain:. At the .beginning of 
the process, during the process, and at the end of the process, the rocks, 
with the exception of an inappreciable amount, are crystallized solids." 
Chapter IX treats of rocks. A classification of the sedimentary rocks 
is given, their genesis is discussed, and the series of transformations 
through which each of the rocks passes is traced out, the, resultant rocks 
being indicated. It was not found possible to give a similar treatment 
for the igneous rocks. 
With the ninth chapter the subject of metamorphism proper closes, 
but the results contained in these nine chapters have an important bear- 
ing upon other parts of physical geology. The remaining chapters con- 
sider these relatfons. 
Chapter X discusses the relations of metamorphism to stratigraphy. 
It is shown that in consequence of metamorphism great difficulties are 
introduced in stratigraphical work. The nature of the difficulties and 
the manner in which they may be overcome are fully considered. 
Chapter XI treats of the relations of metamorphism to the distribu- 
tion of the chemical elements. , This- is perhaps the most daring of the 
various attempts at generalizing of the treatise. It is shown that- as a 
result of the forces and agents of metamorphism the elements of the 
original igneous rocks are redistributed, a given element being less 
abundant in the larger number of sedimentary rocks than in the original 
rocks, and corresponding with this depletion each of the elements is 
segregated in one or more formations. An attempt is made to treat the 
problem of the redistribution of the elements quantitatively. Assump- 
tions are made as to the total mass of the sediments and of the relative 
proportions of the more important classes of sediments. Combining 
these assumptions with the results of chemical analyses, the losses and 
gains of various formations for each of the important elements of the 
earth are considered. Many surprising results are reached. For instance, 
we find the conclusion that to oxidize the ferrous iron of the original 
rocks to the ferric condition in which most of it occurs in the sedimen- 
tary rocks, 35 per cent of the amount of oxygen in the, atmosphere has 
been required. But still more startling is the conclusion that to oxidize 
the sulphur and iron of iron sulphides in order to produce the sulphates 
of the ocean and gypsum deposits, and to transform the iron to the. ferric 
form required one and one-half times the amount now in the atmos- 
phere. 
The final chapter of the book, XII, is upon the relations of meta- 
morphism to ore deposits. It is probable that this chapter will receive 
more general attention than any other. The material of the other 
chapters is of a kind which is likely to be of interest to the geologist 
only, whereas this chapter is of interest to all men concerned in the 
