THE LOWEK HUEONIAN. 313 



(pres^^raably derived from pegmatitic granites), round to subangular grains 

 of cloudy feldhpar, quartz, ragged pieces of biotite altering to chlorite, 

 green hornblende, augite, apatite, zircon, and a large amount of fine inde- 

 terminable interstitial material derived from the trituration of the various 

 materials already mentioned. From the decomposition of this interstitial 

 material, as well as from the associated larger fragments, there has been 

 produced the ' secondary minerals chlorite, calcite, actinolite, sericite, 

 epidote, quartz, feldspar, and pyrite, which occur in large quantity in the 

 sediments. The prevailing green tones of the sediments is especially due 

 to the very large quantity of the green hornblende, epidote, chlorite, 

 augite, and sericite which is present. In a few cases the well-bedded gray- 

 wackes associated with the conglomerates, and especially those near the 

 conglomerates that are composed chiefly of greenstone fragments, are found 

 to consist very largely of fragments of crystals of hornblende, augite, and 

 feldspar, with an occasionally well-preserved entire crystal. Such sedi- 

 ments resemble the crystalline tuffs of volcanic origin. The beautiful 

 bedding and association with other sediments show clearly that these rocks 

 are water-deposited sediments. 



METAMOKPHISM OF THE OGISHKB CONGLOMBKATE. 



It should be borne in mind that the conglomerates thus far described 

 are by no means in their original condition, but have been extensively 

 metamorphosed. This metamorphism has been that produced chiefly by 

 cementation, due largely to infiltration of silica and some calcium carbonate 

 and chemical change of the constituents producing new minerals, and also 

 secondary enlargements of the old minerals. As the result of these changes 

 and additions the conglomerates have been thoroughly indurated. This is 

 the widespread metamorphism which is common throughout all of these 

 Lower Huronian sediments. The kinds of metamorphism now to be 

 described are exceptional; they are not those most common in these con- 

 glomerates. 



The Ogislike conglomerate has been metamorphosed both as the result 

 of orogenic movements and in consequence of the intrusion through it of 

 various granites, as well as of its contact with the Duluth gabbro of Kewee- 

 nawan age. The result of crustal movements is well shown in the schis- 

 tose conglomerate which may be seen at the easternmost point south of the 



