Vol. 50.] THE BASIC ERUPTIVE ROCKS OF GRAN. 



3. The Basic Eruptive Rocks of Gran. (A Preliminary Notice.) 

 By W. C. Brogger, Ord. Professor in Mineralogy and Geology 

 in the University of Christiania, For. Memb. Geol. Soc. (Read 

 November 22nd, 1893.) 



Contents. 



Pacre 



I. Introduction 15 



II. The Olivine-Grabbro-Diabases 18 



III. The Effects of Contact-rnetamorphisni by the Olivine-Gabbro- 



Diabase 21 



IV. The Oamptonites and Bostonites 23 



V. Their Origin by Differentiation 2<J 



VI. Differentiation in the Bosses 31 



VII. Conclusions 35 



Maps 16,17 



I. Introduction. 



Ever since the beginning of the present century, when the first 

 pioneers in the geological exploration of Norway (Keilhau, Haus- 

 mann, Leopold von Buch, and Naumann) investigated the Christiania 

 region, the igneous rocks of that district have been famous as bein^ 

 of more than common interest, as well from the many unique and 

 remarkable rock-varieties as from the exceptionally instructive 

 development of contact-metamorphism produced by the eruptions, 

 and first brought to notice in this region through the observations 

 of Keilhau, Naumann, and Kjernlf. 



In several preliminary communications 1 on the igneous rocks of 

 the Christiania region I have attempted to prove that all the 

 numerous different masses of eruptive rocks within the sunken 

 district between Lake Mjosen and the Langesundsfjord are gene- 

 tically connected, and have followed each other in a regular 

 succession ; the oldest rocks are the most basic, the youngest 

 (except the unimportant basic dykes of diabase) are the most acid 

 and between the two extremes I have found a continuous series. 



Of late years I have proceeded in a more detailed manner with 

 my investigations of the igneous rocks of the sunken tract of 

 country in the Christiania region. I have not as yet in these 

 studies discovered any facts in contradiction to my previously 

 published observations and the deductions founded thereon. On 

 the contrary, more detailed and minute investigation has 011I3- con- 

 firmed the correctness of former publications. 



1 ' Ueber die Bildungsgeschichte des Kristianiafjords,' Nyt Mag. for Xatur- 

 videnskaberne, vol. xsx. (18SC>) p. 99. Also, in a detailed address at the 

 meeting of the Association of Scandinavian Naturalists at Christiania. June 

 1886. A resume was likewise published iu ruy work, 'Die Miueralien der 

 Syenit-Pegmatitgange der siidnorwegischen Augit- und Nephelinsyenite ' 

 Zeitschr. f. Krystallogr, u. Min. vol. xvi. (1890). 



