856 THE JOURNAL OF GEOLOGY. 



Text Book of Geology : By Sir Archibald Geikie, F.R.S. Third edi- 

 tion, revised and enlarged. Pp. i-xvi, 1147. 



The preface to the third edition of this standard text.-book states 

 that it has been entirely revised and in some portions recast and 

 re-written, so as to bring it abreast of the continuous advance of geo- 

 logical science. 



A careful comparison of the third edition with the second indicates 

 that this claim is fully warranted. The general plan of the volume is 

 unchanged, but there are few discussions in which modifications do 

 not appear. In many places the changes consist of nothing more 

 than the addition or modification of a sentence or a paragraph. Even 

 these minor modifications and additions are of great value, since in 

 them are embodied many of the newer facts and ideas which recent 

 research has developed. Thus we find the newer estimates of the 

 average elevation of the continents ; new suggestions concerning the 

 age of the earth ; the introduction of new descriptions of minerals of 

 petrographical importance, and the modification of some upon which 

 new light has been thrown by recent investigations ; the adoption of 

 Rosenbusch's terms for certain rock structures ; the use of the word 

 megascopic in place of macroscopic ; a re-arrangement of rocks upon 

 a genetic basis, as sedimentary, massive or eruptive, and schistose or 

 metamorphic, and a better subdivision under these heads ; throughout 

 the descriptions of rocks, additions and improvements incorporating 

 the more essential facts brought out in recent publications. The pos- 

 sibility of the metamorphic origin of some granites is minimized, and 

 the probability that the greater number of them are eruptive is empha- 

 sized ; the processes of metamorphism are elaborated, and the kinds of 

 mineralization of common occurrence are pointed out. We find, 

 too, new facts as to the amplitude of earthquake waves ; the results 

 of the more recent mathematical calculations concerning the dis- 

 tortions of the sea level by the attractive influence of land eleva- 

 tions ; fuller statements as to the possibility of changes of sea level, 

 and concerning the causes of oscillations of the level of land and sea ; 

 the conclusions to which experiment has led concerning the effect of 

 hot water on the fusion temperature of rock ; new ideas concerning the 

 flow of rock as the result of crushing and pressure ; clear cut state- 

 ments growing out of recent discussions concerning the efficiency of 

 glacial erosion ; a multitude of facts at one point and another drawn 

 from the reports of the Challenger, and from the reports of other deep 



