898 THE GEOLOGY OF MINNESOTA. 



[Conglomerate. 



about their margins, and by these fresh margins they interlock with each other. 

 Their central portions are invariably clouded by decay. 



Quartz unites with feldspar to form the interlocking bond which gives firmness 

 to the rock. There is nothing that can be identified as original clastic quartz. If 

 it ever existed in this rock and it probably did -it has been reformed so that now it 

 is in sharply interlocking grains. This alteration of the quartz appears to have 

 been simultaneous with the new growths of the feldspars. The feldspars did not 

 lose their original forms and identity, but the quartz is wholly transformed. Occa- 

 sionally the quartz is so shaped in contact with a border of a feldspar that it 

 shows it was either later or was not able to resist the recrystallizing force in the 

 feldspar. 



A few rather fresh, long hornblendes are conspicuous for their independent 

 manner of thrusting themselves among the other minerals. There are also many 

 small and irregular ones. The whole of the hornblende is probably of secondary 

 growth, especially the straight and independent crystals; but there is besides a 

 a considerable hornblende which seems to occupy the places of some other 

 original mineral, and some of this is chloritic. They are irregular and imperfect 

 both in form and in cleavages. Indeed, sometimes two dark minerals are curiously 

 and quite irregularly intergrown, having different extinction points. This is 

 . caused by partial uralitization of augites which in part retain still their crystalline 

 integrity. Such augite, however, is quite light colored. 



With some chlorite and accessory amounts of biotite, pyrite and sphene, the 

 foregoing constitutes the mineral contents of this rock. Two sections. 



Age. Upper Keewatin. 



Remark. This rock perfectly exemplifies the manner of conversion of an 

 evidently clastic rock into a crystalline one, and is comparable to several others 

 described from the same region. Its granitization is not so nearly perfect as in some 

 that belong to this belt taken at points further west, but it is more nearly perfect 

 than some which came from the same mass a few miles further east, i. e., from the 

 porphyrel at Zeta lake. 



It is evident that it is difficult to decide, in some such cases, whether 

 the rock should be called granite or graywacke, for it has characters of both. 



N. H. W. 



No. 594G. CONGLOMERATE. ( Gh-anitized. ) 



N. E. % S. W. } sec. 31, T. 65-6, south shore of Kekequabic lake. 

 JKef. Annual Report, xx, page 66. 



Meg. Like the last, but more completely conglomeratic, and in general perhaps 

 a little coarser in the general matrix. 



