'T 



6 POPULAR SCIENCE MONTHLY. 



have been made interested in geology by some of these masterly picturesque 

 descriptions of regions with which they were superficially familiar. Other 

 treatises on the origin of surface features, dealing with the subject more 

 fundamentally, but likewise of limited scope, are not wanting. Yet, as 

 Prof. James Geikie well says, there is no English work to which readers 

 not skilled in geology can turn for a general account of the whole subject. 

 Professor Geikie has therefore prepared his elaborate book on Earth Sculp- 

 ture * to supply this want, to furnish an introductory treatise for those 

 persons who may be desirous of acquiring some broad knowledge of the re- 

 sults arrived at by geologists as to the development of land forms gener- 

 ally. A vast number of geological questions are involved in the exhaustive 

 treatment of the subject. All the forces with which geologists become 

 acquainted in the study of the earth, and their operation, come into consid- 

 eration. The effects of these forces assume aspects that vary according 

 to the nature of the material on which they operate, and they are again 

 modified according to the peculiar combinations of forces at work. The 

 subject is therefore not the easy one it may be supposed at first sight to 

 be, and the reader who peruses Professor Geikie's work with the inten- 

 tion of mastering it will find he has some studying to do. Yet Professor 

 Geikie is clear, and it is only because he has gone deeper than the others 

 that he may be harder. The first point he insists upon is that in the fash- 

 ioning of the earth's surface no hard-and-fast line separates past and pres- 

 ent. The work has been going on for a long time, and is still in progress, 

 under a law of evolution as true for the crust of the globe as for the plants 

 and animals. In setting out upon our inquiry we must in the first place 

 know something about rocks and the mode of their arrangement, of the 

 structure or architecture of the earth's crust. This leads to the distinction 

 between the igneous and the subaqueous, the volcanic, plutonic, and meta- 

 morphic, and the derivative rocks on which epigene agencies have per- 

 formed their shaping work. These rocks have been modified in various 

 ways, and the surface appearance of the earth has been affected by forces 

 operating from the interior, and by external factors, the work of which is 

 called denudation. The agents of denudation are described — air, water, 

 heat, frost, chemical action, plants, and animals — often so closely associated 

 in their operations that their individual shares in the final result can hardly 

 be determined. The various influences of these factors as exerted upon 

 different forms of geological structure and different sorts of rocks are then 

 taken up and described as applied to land forms in regions of horizontal, 

 or gently inclined, and of highly folded and disturbed strata, and in re- 

 gions affected by normal faults or vertical displacements. Land forms 

 due directly or indirectly to igneous action and the influence of rock char- 

 acter on the determination of land forms are subjects of special chapters. 

 Glacial action is one of the most important factors in modifying the forms 

 of northern lands, and is treated with considerable fullness. iEolian action 

 — of the air and wind — has peculiar and important effects in arid regions, 

 and underground water in limestone districts, and these receive attention. 

 Then come basins — those due to crustal deformation, crater lakes, river 

 lakes, glacial basins, and others, and coast lines. Finally, a classification 

 is given of these land forms as plains or plateaus of accumulation and of 

 erosion, original or tectonic and subsequent or relict hills and mountains, 

 original or tectonic and subsequent or erosion valleys, basins, and coast 



* Earth Sculpture, or the Origin of Land Forme. By James Geikie. New York : G. P. Putnam's 

 Sons. Pp. 397. Price, $2. 



