M. Von Buch on Gabbro, 51 



tions of the Geological Society of Cornwall, and in the 2nd volume of 

 that work, there are some observations by Mr. Rogers on the same place. 



Dr. Mac CuUoch mentions diallage rock (Classification of Rocks, page 

 645, &c.) as abounding in the islands of Unst, Balta, and Fetlar, and as 

 occurring also, but in very small quantity, in the northern extremity of 

 the Mainland of Shetland. In Unst and Fetlar it is in contact with ser- 

 pentine. The diallage rock is described as stratified, and alternating 

 with primary schistose rocks, and serpentine. 



Dr. Mac Culloch, in his synopsis of this rock, (p. 649, &c.) separates 

 it into three divisions, as follows. 



First division. i 



Simple ; or of diallage alone. 

 A. A confused mixture of crystals of diallage. 



Second division. 

 Compound ; of two ingredients. 

 A. A mixture of diallage and felspar. 



a. With platy felspar. 



b. With fine granular felspar. 



c. With compact felspar. 

 B; Diallage and actinolite. 



C. Diallage and talc, or chlorite. 



D. Diallage and serpentine. 



Third division. 

 Compound : of three ingredients.' 

 A. Diallage, felspar, and mica. 

 Bj Diallage, felspar, and quartz. 



» 2 



