Processes and their Results. 375 



admitted, however, that sometimes the new aspect has no particular 

 advantage over the old, and indeed is less impressive. For the 

 matured geologist the discussion of difficult problems by the method 

 of " multiple hypotheses," elsewhere advocated by the senior author 

 and here adopted, has many advantages ; but it may be doubted 

 whether the method will commend itself to the geologist in the 

 making, for whom a single aspect of an uncertain question is 

 usually more than sufficient. The book, in fact, possesses the 

 characteristic of much American geological literature, in uniting 

 a mass of simple elementary matter with discussions that demand 

 wide-reaching knowledge of the facts of the science for their proper 

 appreciation. As the authors state, however, that while the work is 

 intended primarily for mature students, it has been framed also for 

 the reader without systematic antecedent knowledge of the subject, 

 the combination of elementary and advanced material is, in this case, 

 unavoidable. Some of the problems raised in the book — as, for 

 example, the discussion of the original composition and internal 

 structure of the earth and its relation to the origin of the igneous 

 rocks and volcanoes ; that relating to the geological history of the 

 atmosphere ; and that dealing with the physics of glacier-movement 

 — embody recent views of the senior author which necessitate 

 considerable modifications in the prevalent conceptions of geological 

 physics. Into these abstruse questions we shall not venture to 

 enter, but we heartily commend them to the attention of philo- 

 sophical geologists, who will find them conveniently brought 

 together and summarized in this book. All that we can attempt is 

 briefly to indicate the contents of the volume. 



The work begins boldly with a " Preliminary Outline " (chap, i, 

 pp. 1-19), which, under the heading of " Astronomic Geology," 

 starts by considering the earth as a planet, with a discussion of the 

 astronoinical conditions that may have produced geological efi"ects. 

 Next, under " Geognosy," the atmosphere, hydrosphere, and 

 lithosphere are successively outlined, their relative proportions 

 illustrated by some striking numerical data, the relation of the 

 ocean basins to the land-surfaces discussed, and the origin of the 

 rock-masses tersely indicated. In chap, ii (pp. 20-52), dealing 

 with "The Atmosphere as a Geological Agent," the work of the 

 wind is fully considered, along with other atmospheric effects, 

 including even the occasional influence of lightning. 



Then follows the longest and most richly illustrated chapter in 

 the book (chap, iii, pp. 53-201), on "The Work of Running 

 Water," wherein all the recent ideas with respect to physiographic 

 development are conveniently brought together and supported by 

 appropriate examples from all parts of the United States. The 

 broad generalizations on this subject are illustrated by some 

 geometrical and other designs (figs. 45-51) of remarkable aspect, 

 that look as though they had wandered out of textbooks of 

 crystallography and biology. In the next chapter (iv, pp. 203-231) 

 " The Work of Ground- (Underground) Water " receives treatment, 

 the solvent and other effects of such waters being duly considered. 



