Decembeb 31, 1909] 



SCIENCE 



969 



must conclude that the local reservoir of an 

 individual volcano is supplied by drafts from 

 some much larger body of rock magma with 

 which it is from time to time in communica- 

 tion. The various types of igneous intrusion 

 are then considered, especial attention being 

 paid to the numerous varieties of laccolitic 

 and bathylitic intrusion. The important ques- 

 tion of petrographical provinces and the mu- 

 tual relations of associated igneous rocks are 

 discussed at length. While recognizing many 

 local and subordinate petrographical prov- 

 inces, Mr. Harker distinguishes two petro- 

 graphical regions of the first order of magni- 

 tude, an Atlantic and a Pacific region, the two 

 being separated in America by the line of the 

 Andes and Cordillera folding. The former 

 region is characterized by a prevalence of 

 magmas rich in aUcalis, while in the magmas 

 of the latter, lime and magnesia are relatively 

 more abundant. The mutual relations of the 

 magmas in a number of well-known igneous 

 areas within these great petrographical re- 

 gions is then considered and is illustrated by 

 the aid of variation diagrams. 



A very interesting and valuable portion of 

 the book is that in which the physical chem- 

 istry of rock magmas and the laws which gov- 

 ern their crystallization is considered. In this 

 results of the recent researches of Vogt, Miers, 

 Day, Doelter and others are presented and 

 critically discussed. The structures of igneous 

 rocks are also considered in the light of 

 recent work in the field of physical chemistry. 

 Thus in hypabyssal porphyritic rocks, the 

 phenocrysts often represent the excess over 

 eutectic proportions and the ground mass the 

 quasi eutectic residuum, while in the volcanic 

 rocks the distinction is obscured by the ef- 

 fects of the discontinuous change of physical 

 conditions at the time of extrusion. Micro- 

 graphic intergrowths, corona, spherulitic and 

 variolitic structures are explained in the light 

 of the laws of crystallization as elucidated by 

 recent studies in physical chemistry. 



The function of mineralizers in rock mag- 

 mas and the formation of certain minerals 

 through their agency is then discussed, lead- 

 ing to the consideration of the active role of 



the volatile constituents, which on the crystal- 

 lization of the rock enter upon a new phase of 

 activity, partly of a destructive kind to which 

 Bunson applied the term pneumatolitic. Then 

 follows the consideration of the metasomatic 

 changes developed in certain rocks when 

 penetrated by igneous intrusions, more espe- 

 cially the phenomenon termed " granitization " 

 by the French geologists. 



The very important question of magmatic 

 differentiation in its various phases is then 

 considered, together with the allied question 

 of hybridism in igneous rocks to which Harker 

 has recently made such important- contribu- 

 tions as the result of his studies in the west- 

 ern islands of Scotland. 



The last chapter deals with the question of 

 the classification of igneous rocks. The 

 " quantitative system " is adversely criticized 

 and the opinion is expressed that a satisfac- 

 tory classification can not be expected until 

 our knowledge in the domain of petrogenesis 

 is much more extended than it is at present. 



The work traverses a portion of the field of 

 geological knowledge which is not covered by 

 our ordinary text-books, although many of 

 the questions discussed are also treated of in 

 the first volume of Professor Iddings's work 

 on " Igneous Pocks," which has just appeared. 

 It is well and clearly written and will repay 

 a careful perusal by all interested in the mod- 

 ern developments of the science of geology. 



McGiLL Unitorsitt Prank D. Adams 



Croisiere Oceanographique accomplie a lord 



de la Belgica dans la Mer du Gronland, 1905. 



Due d'Orleans. Bruxelles, 1907. 4to, 5Y3 



pp., 80 plates and charts. 



In June, 1905, the Duke of Orleans, having 

 in view a study of the Greenland Sea, sailed 

 from Tromso, Norway, in the well-knovra 

 steamer Belgica, commanded by A. de Ger- 

 lache de Gomery, accompanied by an effective 

 staff. The season being too early for naviga- 

 tion on the Greenland coast the course of the 

 expedition was laid first to the northward by 

 Bear Island, the west and north coasts of 

 Spitzbergen, and then as closely as opportu- 

 nity permitted skirted the compact southward 



