854 THE GEOLOGY OF MINNESOTA. 



[Conglomerate. Granite-porphyry. 



made up largely of small feldspar fragments, of hornblende and chlorite, with some 

 quartz, and of devitrified glass in small grains, and of sphene. One section. 



Age. Archean (Upper Keewatin). 



Remark. This rock terrane, which is a large and important one in the region, 

 can safely be parallelized with the Ogishke conglomerate, and especially with the 

 conglomerate at Zeta lake. It sometimes takes the character of the Stuntz conglom- 

 erate, as seen on the ridge between Moose and Flask lakes. (Compare remark under 

 No. 2189). N. H. w. 



No. 2187. CONGLOMERATE. (Porphyrel.) 



Shore of Snowbank lake, near the centre of sec. 26, T. 64-9. 

 Ref. Annual Report, xxiv, page 57. 



Meg. A condition of the conglomerate of the region, having conspicuous feld- 

 spars. Compare No. 1062. 



Mic. The large feldspars are much twinned, like all those in this curious 

 conglomerate, but are permeated by the same kind of alteration, viz., the production 

 of innumerable scales of mica. In this case epidote, and occasionally a secondary 

 feldspar with different orientation, are plainly shown. This secondary feldspar is 

 also sparsely distributed in the matrix as an interlocking groundmass and as an 

 interlocking fringe about the crystals. Epidote is quite abundant in the chloritized 

 hornblende areas and sphene is in the matrix in sparse grains. One section. 



Age. Archean (Keewatin). N. H. w. 



No. 2189. GRANITE-PORPHYRY. 



At the point, S. W. J^ N. E. ^ sec. 26, T. 64-9, Snowbank lake. 

 Ref. Annual Report, xxiv, page 57. 



Meg. This rock acts as dikes cutting mica schist. It contains green pebbles, 

 and is cut by later granite intrusions, i. e., by the prevailing granite of Snowbank 

 lake. 



Mic. This is a wholly crystalline rock, but it has two dates of crystallization. 

 The large feldspars are "old feldspars" in the sense that they became much altered 

 and were then regenerated. The alteration products are largely mica, talcite, and 

 epidote. Throughout they are renewed by the formation of new feldspars, often 

 globular in form, and still more frequently in the form of an interlocking fringe or 

 exterior zone which surrounds them and unites them with the fine feldspathic 

 matrix in which they lie. They are plainly twinned (albite plan) and their nearly 

 parallel extinction indicates for some of them a composition near oligoclase, but they 

 are considerably broken up by the growth of a finer interlocking structure with differ- 

 ent orientations. This finer structure is not always of freshly developed material, 

 but is clouded with the same impurities as the unbroken crystal, showing that the 



