THE LOWER HURONIAN. 309 



OGISHKE CONGLOMERATE. 

 PETEOGRAPHIC CHARACTERS. 



Macroscopic characters. — The Ogishke conglomerate varies from a 

 coarse bowlder conglomerate with bowlders up to 20 inches in diameter, as 

 shown on the southwest side of Cache Bay of Saganaga Lake, down 

 through all intermediate gradations of coarseness into rocks which are 

 designated as grits, and through these into slates. The grits are, of course, 

 interbedded with the conglomerates, but no attempt has been made to 

 separate them from the conglomerates on the maps where it was recognized 

 that they occurred in very subordinate quantity. The conglomerates contain 

 a great variety of pebbles. We find among these a great number of kinds 

 of altered basic eruptives, both massive and schistose, coarse and fine 

 grained, porphyritic and nonporphyritic, amygdaloidal and nonamygdaloi- 

 dal, some showing flowage lines produced by parallelism of the feldspars, 

 and others with spherulitic structure. Among the most striking of these 

 are the porphyritic rocks in which the feldspar and hornblende are the 

 phenocrysts and occur either alone or together. Upon one ledge seven 

 different kinds of greenstones were counted. The granites which occur in 

 pebbles and bowlders in the conglomerates show varieties ranging from 

 coarse and fine evenly grained to porphyritic and nonporphyritic forms. 

 There are several kinds of fine-grained acid porphyries also. A few 

 slate fragments and two fragments of a conglomerate were likewise seen 

 in the coarse elastics. Black and gray chert, jasper, vein quartz, and a 

 number of fine-grained gray pebbles, whose characters were undetermined, 

 occur associated with those mentioned. 



The brilliant red-jasper fragments lying in the green matrix give the 

 conglomerate a very handsome appearance. With this jasper-bearing 

 conglomerate, and a phase grading over into the Knife Lake slates, there 

 occurs a dark-green medium-grained graywacke with a faint speckling, due 

 to the small, bright-red fragments of jasper scattered through it. The 

 amount of small jasper fragments varies in quantity, being rare in some 

 cases, and in others so numerous as to influence very markedly the color 

 of the graywacke. 



Many of the jasper fragments which occur in this conglomerate possess 

 a well-developed zonal structure. The centers of the fragments are red 



