88 



TKNITI KSKOI.A. 



M.-X. Kl. 



Sp. 



'^..12 (t 



12 ). 



Auvergno.se, III, 5, 4" 3. 



I hi.s is a very typical and common gabbroid composition. The Aardal 

 rock belongs to that division of the Caledonian erupti\-es by Y. M. Gold- 

 schmidt called the Bergen jotun stem iStamml'. An important part of 

 these rocks, the so-called Jotun norite.s, are characterized by a high pro- 

 portion of potash, the composition in other respects being noritic. This 

 characteristic is not very pronounced in the rock under consideration, nor 

 does it contain perthitic feldspar, so typical of the Jotun norites, and it 

 may be therefore classed with the normal-gabbroid branch of this "stem". 

 To show the close similarity with another member of the same branch, we 

 will quote the analysis made by M. Dittrich of saussurite-amphibolite, a 

 metamorphic derivative of a normal-gabbroid Jotun rock without garnet 

 from Framnaes, South and of Tyin lake, Jotunheimen (Goldschmidt op, cit. 

 p. 28), I. 



Analysis II made by M. Dittrich (op. cit. p. 38) is one of typical jotun 

 norite from Breikvamsnaase, Jotunheimen. Ill is the garnet-gabbro from Aardal. 



The most abundant mineral of the garnet-gabbro is plagioclase and 

 second in abundance is the garnet. Thereafter follow clinopyroxene, biotite, 

 hornblende, hypersthene and titan iferous iron ore. 



The composition of the plagioclase conforms to Ab-^,, .showing in 

 sections _|_ PM y' : M = 11". This angle was measured in numerous crvstals 

 and there seems not to exist any zonal developm.ent or other kinds of 

 heterogeneity. 



' Op. cit. iVid.-Selsk. Skrifter. I. Mat.-Naturv. Kl. 191 6. N:o 2I. 



