GEOLOGICAL EXPLORATIOXS AND LITERATUKE— 186.J. 41 



simph- because of the great litliologioal difFerences between the two sets 

 of rocks. Following these schists to the soutli is — 



a series of augitic rocks aud schists, interstratified with magnesian hydrous rocks 

 and slates, .the two kinds of rocks being represented on the one hand by liypersthene, 

 pyroxene, and bedded diorite passing into diorite-shites, and on the other by takiose 

 aud chloritic schists. The former character of the rocks prevails to such an extent 

 as to impart to the lower members of the Huronian series a distinctively augitic 

 aspect. The several rocks composing this augitic zone are commonly of a greenish 

 color, and vary in this respect chiefly as to shade, resembling iu this particular the 

 lower slate-conglomerate which marks the base of the series in Canada, and from 

 ■which they seem to differ only in the absence of pebbles and bowlders from the 

 subjacent Laurentian rocks, which there form a distinguishing feature. (P. 294.) 



From this quotation it is plain that the author regards these green 

 schists as of sedimentary origin, and as forming the lower division of the 

 Huronian series. South of these are the <|uartzites, slates, and other 

 plainly fragmental rocks, which "are associated with greenish hornblendic 

 slates and more or less crystalline diorite, and at their base with bands of 

 dolomite, somewhat siliceous and highly altered." (Jverlying the quartz 

 zone are the ores of the region, associated with talcose, argillaceous, and 

 siliceous schists. These are thought to be the equivalents of the upper 

 slate-conglomerate of the north shore, which is Upper Huronian. The 

 ores are specular schists and conglomerates and earthy red hematites. 

 The conglomerates are described as resting ujjon diorites and chlorite- 

 schists in some cases, and ixpon dark quartzites in others. The ervstalliue 

 rocks of the Huronian are regarded as metamorphic as well as the schists. 

 No "trappean overflows" were observed, as were reported by Foster and 

 "Whitney. Thus Kimball seems to place himself alongside Rivot in denying 

 the igneous origin of any of the larger masses of greenstone in the region, 

 while at the same time he acknowledges the igneous nature of the smaller 

 dikes. 



In addition to his discussion of the general relations of the Marquette 

 rocks, the author attacks the prolilem of the genesis of the ores, and 

 declares very strongly in favor of their sedimentary origin. This is the 

 first time any definite statement had been made in contradiction to I'oster 



