460 



REGINALD E. HO RE 



which are generally conformable but in some localities separated 

 by a slight unconformity. 



The upper series is made up largely of medium-grained feld- 

 spathic quartzite with a little conglomeratic material. It presents no 

 unusual feature and doubtless represents the hardened accumulation 

 of a feldspathic sand derived from siliceous holocrystalline igneous 

 rocks of the Laurentian group. 



The lower series is made up largely of conglomerate, shale, gray- 

 wacke, and feldspathic quartzite. In many cases there is gradual 



Fig. I. — Huronian congbmerate near Temagami, Ont. 



gradation vertically from one of these types to another. Less often 

 there is a sharp division line. The composition of one stratum is 

 often fairly constant for some distance; but in some cases a distinct 

 change takes place in a few feet laterally as well as vertically. 



The shales are for the most part of gray color, less often greenish 

 black. Occasionally they are interbanded with layers of purple, 

 green, and pale-gray colors. The chief recognizable minerals are 

 quartz and altered feldspars, minute scales of chlorite and sericite, 

 and small grains of epidote, titanite, and iron ores. In mineralogical 

 and chemical composition they are not unlike green shales of other 

 formations. 



The quartzites are in most instances feldspathic and grade insen- 



