TRANSLATIONS AND NOTICES 



GEOLOGICAL MEMOIRS. 



MiNERALOGiCAL RESEARCHES i?i the District around Arendal, 

 and Krageroe in Norway. By David Forbes, F.G.S., 

 A.I.C.E., and Tellef Dahll, Cand. Min. 



[Mineralogiske lagttagelser omkring Arendal og Krageroe, &c. ; abridged from the 

 Norske Magazin for Naturvidenskab, vol. viii. part 3, 1854.] 



This paper is the first of a series of observations on the mineralogy 

 of the hne of coast connecting the towns of Arendal and Krageroe in 

 Norway, and contains notices of several new minerals, as well as 

 additions to the mineral geography of this district. 



Some points connected with the development of minerals in con- 

 nexion with the granitic rocks appear of sufficient interest to warrant 

 an abstract of this part of the paper, without going into the more 

 purely mineralogical details which form the bulk of the communi- 

 cation. 



The district itself is composed entirely of the older rocks, princi- 

 pally gneiss, which shows itself in many varieties. The general 

 strike was found to be from 60° N.W. to E. and W., or about parallel 

 to the main line of coast. 



The dip was extremely variable, and at all angles from 13° up to 

 90°, S.E. to S., and up to S.W. 



Mica-gneiss was found most normal in Dybvaag, consisting there 

 of red orthoklase, grey quartz, and black mica. 



Felspar and mica became more sparingly distributed towards Kra- 

 geroe, and there hornblende and quartz were found more prominent, 

 and often as distinct rocks ; on the other hand, nearer Arendal, fel- 

 spar was much more abundant, and was generally present as potash- 

 felspar, whereas at Krageroe soda- felspar was the more common. 



The results of these researches appear to prove that the occurrence 

 of minerals in these rocks is due almost exclusively to the appearance 

 of granite, which therefore formed a special subject of investigation, 

 and is divided into two classes : — 



A, when occurring as veins, or imbedded in the course of strata. 



B, as nodules or irregular masses. 



It was found that this classification was not only consistent with 

 the external form of the granitic masses, but was also visible in their 



VOL. XI. — PART II. C 



