THE GENESIS OF IGNEOUS ROCKS 



By JOHN W. EVANS, D.Sc, LL.B. 



Imperial Institute and Birkbeck College, London 



In recent years considerable attention has been given to the 

 study of the microscopical characters of igneous rocks as well 

 as to the investigations of their mode of occurrence in the field. 

 The work, however, has been in the main descriptive, and much 

 remains to be done in interpreting the data that have been 

 accumulated. It is impossible, in this instance, to follow the 

 procedure usually adopted by geologists and decipher the 

 memorials of the past by the experience of the present ; for 

 the processes involved are, as a rule, far removed from our 

 observation, and even in the case of volcanic phenomena which 

 are visible at the surface there are obvious difficulties in 

 submitting them to close examination. The aid of other 

 sciences has accordingly been invoked, and by the application 

 of physical and chemical principles, many of them of com- 

 paratively recent development, results of considerable interest 

 and importance have been arrived at. These have hitherto 

 been so scattered among different publications as to be to a 

 large extent inaccessible to those interested in the subject, 

 and we owe a debt of gratitude to Mr. Harker, who, in his 

 Natural History of Igneous Rocks, has presented them to us in 

 a readable and attractive form. 2 



No one could have been more fitted for the task. In his 

 classical researches on the igneous rocks of North Wales and 

 the Lake District, and in later years on those of Tertiary age in 

 the West of Scotland, he has demonstrated the relations that 



' The Natural History of Ig?ieous Rocks. By A. Harker. [Pp. xvi + 384.] 

 (London : Methuen & Co., 1909. Price 12s. 6d. net). — Igneous Rocks, Vol. I., 

 Composition, Texture and Classification [pp. xi + 464]. (New York : John 

 Wiley & Sons ; London : Chapman & Hall, Ltd., 1909. Price 21^.) 



2 Two articles by Mr. Harker with the same title appeared in the earlier 

 issue of Science Progress, vol. vi. 1896, pp. 12-33, an d vol. vii. 1898, pp. 203-18. 

 He had previously contributed other petrological articles to the same publication. 



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