824 THE GEOLOGY OP MINNESOTA. 



[Pebbles. Graywacke. Greenwacke. 



No. 2019. PEBBLES. 



"Pebbles in contact near the lake, on the east side, showing remarkable differences; one lot (a) are coarse 

 and specked by white feldspars in a greenish matrix, and another lot (b) are very fine grained." Near the same 

 place as No. 2016. 



Ref. Annual Report, xxiv, page 13. 



Meg. "The first specimen (a) appears to be a quartz-porphyry with small 

 porphyritic quartzes and numerous feldspars. The matrix is very fine grained and 

 dark colored. The second specimen (b) is a very fine-grained, gray, siliceous rock. 

 No section. 



Age. Pebbles in Upper Keewatin. u. s. G. 



No. 2020. GRAYWACKE. 



Same place as No. 2016. 



Ref. Annual Report, xxiv, page 14. 



Meg. Fine grained layer ten feet thick, overlying a bed of conglomerate 

 conformably. 



Mic. Even grained assemblage of feldspar and quartz fragments, lying in a 

 scant matrix of sericite and debris of the same sort. Much of the apparent matrix 

 has resulted from a granulitic alteration of some of the finer feldspars, as in No. 2018. 

 One section. 



Age. Upper Keewatin. N. H. w. 



No. 2021. GRAYWACKE. 



The same place. 



Ref. Annual Report, xxiv, page 14. 



Meg. At ten feet from the conglomerate. Forms a bed ten feet thick. 



Mic. Essentially the same as No. 2020; more evidently some of the feldspar 

 fragments have taken on the fine granulitic alteration structure seen in many cases 

 in the feldspar grains of the Ogishke conglomerate, thus resembling devitrified glass. 

 One section. 



Age. Upper Keewatin. N. H. w. 



No. 2022. GREENWACKE. (Sheared.) 



Same place as No. 2016. 



Ref. Annual Report, xxiv, page 14. 



Meg. Forms a conformable layer two feet thick. Greenish, slightly fibrous, but 

 containing pieces or pebbles of rock like No. 2013, etc. 



Mic. This is one of the sheared, alte'red fragmentals which at first must have 

 contained a considerable amount of some ferromagnesian mineral which now is 

 altered to a chloritic mineral. In the midst of this are some evident feldspar forms 

 and many not so evident, since they are replaced by the usual finely granulitic 

 secondary growth already mentioned, and at the same time very much calcite has 

 been deposited. One section. 



Aye. Upper Keewatin. N H w 



