910 THE GEOLOGY OP MINNESOTA. 



[Quartz-porphyry. Schist. 



noted. Besides the large feldspars there is also one large bipyramidal quartz crystal. 

 One section. 



Age. Keewatin (Lower). 



Remark. The appearance of this section indicates a clastic rock rather than 

 an igneous one. There is no apparent schistosity in the slide. The rock is of a 

 common kind. N. H. w. 



No. 25W(bis). QUARTZ-PORPHYRY. 



S. E. % N. W. y sec. 3, T. 62-14, south side of Mud lake. 

 Ref. Annual Report, xv, page 27. 



Meg. Light gray, nearly massive. 



Mir. Like No. 24W, except that the feldspars are not so far decayed. One feld- 

 spar shows a large embayment, as if produced in the magmatic state. This rock, 

 like the preceding, is slightly reconstructed after long decay, by the formation of 

 new feldspar and quartz which interlock throughout the fine matrix, while a new 

 feldspar substance has generally not replaced the original species, at the same time 

 that most of the fine inclusions have had birth. These inclusions are evenly distrib- 

 uted or are most abundant about the ragged edges of the feldspar sections. The 

 old feldspars are best preserved at their centres, and they have no marginal new 

 growths. One section. 



Age. Lower Keewatin. N. H. w. 



No. 26W. SCHIST. (Flinty.) 



S. E. Yi N. W. % sec. 3, T. 62-14, south side of Mud lake. 

 Ref. Annual Report, xv, page 27. 



Meg. Bluish, fine, compact, jointed like the quartz-porphyry. 



Mic. Exceedingly fine, without large feldspar forms, yet this slide shows a few 

 apparently fragmental pieces of feldspar. The rest of the rock is much darker 

 between the nicols than the foregoing, and this darkness is seen to be due (on 

 lowering the lower nicol) to the presence of much finely divided chlorite and highly 

 refractive epidote with a little sphene. One section. 



Age. Lower Keewatin. 



Remark. This is not known to be separable either structurally or petrograph- 

 ically from No. 25 W. N. H. w. 



No. 27W. SCHIST. (Flinty.) 



S. E. % N. W. y sec. 3, T. 62-14, south side of Mud lake. 

 Ref. Annual Report, xv, page 27. 



Meg. Gray, fine, hard, but internally somewhat conchoidally brecciated. 

 Mic. Like No. 26W, but having somewhat larger and more numerous feldspar 

 grains, but not approaching the porphyritic aspect of No. 24W. One section. 



Age. Lower Keewatin. N. H. w. 



