742 REVIEWS 



assimilating them. He cites cases from the Christiania region where 

 the granite has intruded the sedimentary beds in such a way that a 

 portion of the latter has disappeared. The invading rock has meta- 

 morphosed the sediments, but the contact is sharp, and the granitite, 

 which is normally very poor in lime, shows no chemical enrichment 

 through "assimilation" of the calcareous beds with which it is in con- 

 tact. During years of study, over magnificent exposures, in the 

 Christiania region, Brogger has found no evidence in favor of any 

 assimilation of the invaded sediments, nor for their "feldspathization" 

 by the intruding magma. If the granite, then, has not absorbed the 

 missing beds, where have they gone? They must, he says, be under- 

 neath the plutonic mass. "The plutonic rocks of the Christiania 

 region have been brought into their present position by purely 

 mechanical processes — by a squeezing up, and subsequent lateral 

 intrusion, as a consequence of great subsidences of neighboring 

 portions of the earth's crust. Their composition is not essentially 

 influenced through assimilation of salbands, or through fusion of the 

 overlying strata, but is the final result of differentiation processes of 

 the original magma of the common magma-basin from which they all 

 come. Their typical form is the '■Kuchenform'' of the laccolith." It is 

 possible, however, that the Michel-Levy assimilation hypothesis and 

 the Suess batholith hypothesis may apply to the great granite regions 

 of the older ^^ Grundgebirge'' or to districts of folded, regionally 

 metamorphosed rocks, but Brogger evidently considers it improbable. 



The eruptive sequence of the Tyrolean region is compared with 

 that of the Christiania region, and the facts are considered to support 

 the view previously advanced by Brogger, that the differentiation 

 sequence and the eruptive sequence are dependent upon the sequence 

 of crystallization. The chemical composition of the hypothetical 

 primary magma of the Austrian region is calculated by the method 

 employed for the Christiania region in the preceding paper on the 

 Grorudite-Tinguaite Series, and is found to have about the same silica 

 percentage (65.2, as compared with 64.2 for the Christiania magma) 

 but is rich in lime and poor in alkalies, while the Norwegian magma is 

 poor in lime and rich in alkalies. 



The paper concludes with some general considerations on the 

 eruptive sequence of plutonic rocks. Such sequences are very difficult 

 to work out in the field, and to be of service in determining the laws 

 in accordance with which the differentiation processes have taken place 



