148 Scientific Intelligence. 



before various learned societies, while others have been published 

 in various periodicals. Of the fourteen chapters of the book, one 

 discusses the general relations between geography and geology, 

 with special reference to methods of teaching geography ; three 

 are descriptions of the geology of Scotland, or of particular facts 

 of that country; four treat of the evolution of the main geo- 

 graphical features of the earth ; and six are devoted to the dis- 

 cussion of various phases of the Glacial Period. The dates of 

 delivery or publication of the articles range from 1876 to 1892. 

 As each article was intended to be complete in itself, and they 

 have been republished in the present volume with little i-evision, 

 there is ineyitably considerable repetition. But each article is a 

 valuable contribution to the knowledge of the subject of which 

 it treats. Without attempting to notice the several articles in 

 detail, we propose to call attention to some of the most important 

 conclusions, in relation to the two important subjects to whose 

 discussion the majority of the papers are devoted. 



I. Geographical Evolution. 



The author maintains the doctrine of the permanence of conti- 

 nents and oceans, giving credit to Professor Dana for the first 

 clear enunciation of that doctrine.* In support of that doctrine, 

 he refers to the contrast between the formations in progress at 

 the bottom of the ocean, as made known by the naturalists of the 

 Challenger and other expeditions for the investigation of the 

 ocean, and the materials of which the surface of our continents 

 and islands consist.f Certain it is that the rocks of existing land 

 surfaces are in general very different from the volcanic clays and 

 organic oozes of the ocean floor. 



Assuming the substantial permanence of continent and ocean, 

 in the sense of areas respectively of relative elevation and rela- 

 tive subsidence, the author holds that the progressive relative 

 subsidence of the ocean basins has led to a progressive emergence 

 of the continental areas, and accordingly a progressive increase in 

 the area of dry land. That, in spite of all oscillations, this has 

 been the general course of geological history, there seems little 

 reason to doubt. A very interesting series of maps is given,J 

 showing the areas of land and sea in Paleozoic, Mesozoic, and 

 Cenozoic times, respectively. It is needless to say that the indi- 

 cations given by these maps are intended only as approximations ; 

 but they present a picture of geographical evolution whose main 

 outlines are doubtless true. These maps are accompanied by a 

 fourth, in which the areas respectively of dominant depression 

 and elevation are distinguished, the contour line of 1000 fathoms 

 being taken as the boundary. This boundary, is, however, recog- 

 nized as an arbitrary one,§ since it is obvious "that the true 

 boundary of the continental plateau cannot lie parallel to the 

 surface of the ocean." 



* Page 326. f Page 327. % Plate v - 



8 Page 378. 



