800 THE GEOLOGY OP MINNESOTA. 



[Gabbro. Amygdaloid. Aporhyolyte. 



than the peripheral, and in the peripheral portion quartz shows itself in vermicular 

 outlines. The slate shows no tourmaline, but there is a little sphene, leucoxene and 

 epidote. One section. 



Age. Cabotian. 



Remark. In this red granite, as is frequent, there are visible traces of the 

 elements of the basic intrusives (gabbro, etc.). These consist of sphene, leucoxene 

 and the triclinic feldspars, and this fact seems to illustrate the principle which is 

 common in these contact rocks that the acid elements of the clastic rocks permeate 

 and easily destroy the elements of the gabbro, while the gabbro elements are more 

 slow to enter the acid rock. N. H. w. 



No. 1855. GABBRO. 



About one mile west of the west point of Grand Portage bay. From a dike forming a little point at the 

 Lake Superior shore. 



Ref. Annual Report, xxii, page 10. 



Meg. Evidently a basic and diabasic rock. 



Mic. The augites and olivines were earlier than the feldspars. The rock has 

 somewhat decayed, so that the olivine is principally changed to a yellowish serpen- 

 tine or antigorite, and leucoxene appears in small quantity, while calcite and quartz 

 have entered, the latter in form of a somewhat vermicular micro-pegmatyte in the 

 feldspar. One section. 



Age. Manitou(?) N. H. w. 



No. 1856. AMYGDALOID. 



Cut by the dike No. 1855. 



Ref. Annual Report, xxii, page 10. 



Meg. Over large areas this rock shows a distinct cellular structure. 



Mic. The slide shows simply a much altered diabase, in which the augite which 

 was ophitic in its relation to the small feldspars has been entirely changed to a 

 greenish, isotropic so-called chloritic, substance, while much calcite has been isolated 

 in abundant, irregular bunches, and larger, irregular spaces are occupied by a finely 

 granular material which cannot be completely separated, but apparently consists of 

 the same chloritic substance in large part, through which are disseminated minute 

 polarizing grains resembling feldspar and quartz, with leucoxene and magnetite. One 

 section. 



Age. Cabotian(?) N. H. w. 



No. I860. APOUHYOLYTE. (Amyy<l<il<>i<lal.) 



South town line of T. C2-1 E., where the new road from Grand Marais crosses it. 

 Ref. Annual Report, xxii, page 10. 



Porphyritic with quartz, and also amygdaloidal. 



