REVIEWS 209 



modes of alteration of the leading rocks are discussed in detail. Per- 

 haps the most valuable contribution of the book is the series of analy- 

 ses of identical rock at varying stages of decomposition, by means of 

 which the nature of the process, in so far as it is chemical, is specifically 

 and precisely indicated. These tables show in just what degree the 

 process acts differentially upon the several constituents of the rock. 

 Although the analyses are not sufficiently numerous to warrant very 

 broad generalizations, they are very helpful in giving approximate 

 knowledge of the relative parts played by the several constituents of 

 rock in the disintegrating process. The results of the analyses are 

 conveniently indicated in separate columns which severally show the 

 percentage of loss for the entire rock, the percentage of each constituent 

 saved, and the percentage of each constituent lost. These special 

 studies are followed by a resume embracing general deductions drawn 

 from them. 



The chapter on the physical manifestations of weathering treats of 

 the more familiar effects of the process on texture, color, surface con- 

 figuration and similar features. This is followed by an interesting chap- 

 ter on time considerations, in which are treated the rates of weathering 

 and the influence of position, texture, composition, humidity, temper- 

 ature and other climatic conditions upon the progress of the process. 



The mantle of loose material which results from the weathering, 

 together with loose material accumulated on the surface by other 

 agencies, the author designates regolith (mantle rock), and devotes the 

 last 100 pages to its description. It is not altogether clear whether the 

 simple fact of mantling the surface with loose material is sufficient to 

 unify accumulations arising from quite diverse agencies and varying 

 greatly in nature, and hence to call for a specific name of the petro- 

 graphic form. The residuary clays and earths constitute a unitary 

 formation derived directly by the processes of weathering. The 

 glacial, eolian, and similar deposits can only be brought into the same 

 category by largely neglecting their mode of origin and confining atten- 

 tion merely to their superficial disposal and their incoherent character. 

 It may well be questioned whether the genetic factor in these cases will 

 not usually be the one to be kept at the front, and be more often placed 

 in contrast to the residuary earths than merged with them. Doubtless, 

 however, the mantling feature which they possess in common will make 

 the term regolith often convenient. The word at any rate may be left 

 to stand or fall as experience shall dictate. 



