920 THE GEOLOGY OF MINNESOTA. 



[Conglomerate. 



the most conspicuous and coarsest parts of this rock. Some of the quartz is in indi- 

 vidual grains, but some was originally an interlocking multiple quartz with rounded 

 outlines. Actinolite forms the chief coloring element, being in confused, fibrous, 

 matted and fine mass which surrounds the quartz and which in form of rosettes 

 penetrates the quartz about its borders, and which is in general much chloritized, or 

 at least is associated with chlorite. Besides these are pebbles that appear to have 

 been feldspars of detrital origin, but now consist wholly of micro-granulitic replace- 

 ment, the grain (or pebble) maintaining its size and form in the midst of the green 

 matrix. In other parts the matrix does not consist of this green substance, but of a 

 mixture of all the other elements in fine granules, including also some mica and 

 epidote, and in others it is of the same fine interlocking quartz-feldspar mosaic as has 

 replaced the feldspars. Sphene is scattered in the section. One section. 



Age. Pokegama. 



Remark. It is remarkable that in this rock, while all the fine clastic feldspars 

 of the matrix, and also several large ones which now are still evident in their outlines, 

 have been replaced, as above stated, by a quartz-feldspar mosaic of fine grain, there 

 remains one large labradorite which has not been affected in that way. Compare 

 No. 366H, where it is shown that pebbles of originally micro-granulitic quartzyte(?) 

 are embraced in a conglomerate similar to this. It is hence probable that this 

 supposed replacement of old feldspars is not tenable, but that these were also original 

 pebbles of micro-granulitic quartz, perhaps from jaspilyte of the Lower Keewatin. 



No. 366H. CONGLOMERATE. 



S. W. y sec. 13, T. 60-13, north end of Iron lake. 



Ref. Annual Report, xvii, pages 84, 136. (Compare Nos. 364H, 370H.) 



Meg. Conglomerate, rather coarse. 



Mic. Six sections made from this rock are calculated to show its composition: 

 1. A piece of granite, consists largely of quartz and microcline, the latter being inter- 

 grown with another feldspar in manner of a microperthite, and also containing 

 numerous isolated small crystals of some triclinic feldspar, the microcline having 

 embraced them pokilitically, and being much more preserved than the inclusions. 

 The same crystal of microcline also embraces a crystal of sphene. Besides microcline 

 the slide contains several large but considerably decayed feldspars, which have a 

 close albite twinning and are probably oligoclase. Chlorite, some of which is pennine, 

 Muscovite, epidote and more or less iron oxide (limonite ?) also appear as alteration 

 products. 2. At first this slide appears much like No. 1, but it differs in having a 

 matrix matter of green, tine, granular hornblende (with some chlorite) which in 

 some places is abundant and forms a large proportion of the slide, and in others is 

 only a narrow band between the large grains, and yet in others is absent, allowing 



