220 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1932 



throughout the whole course of geologic history since pre-Carabrian 

 times. 



Coleman goes on to say : 



Much of the southern shore appears to be a true igueous gneiss often of a 

 pink color, but in the north, eruptive gneisses are relatively uncommon, seldom 

 cover a large area, and the pink color is wanting. Whether pink or gray, the 

 true gneisses are essentially foliated granites made up of feldspars, quartz, and 

 dark mica. In the few sections studied under the microscope the feldspars are 

 seen to be chiefly orthoclase or microcline, with a subordinate amount of 

 plagioclase having a small extinction angle (oligoclase). The quartz often 

 shows strain shadows and in some specimens porphyritic feldspars are tailed 

 out into augen, showing that the rock had undergone shearing strains. 



At one place lit-par-lit injection was seen as well as later dikes 

 of pegmatites or granites. Basic rocks are also abundant, many 

 having the composition of quartz diorite schist. Some rocks col- 

 lected as average gray gneisses turned out to be gneissoid norites. 

 Typical norites, consisting of nearly equal parts of plagioclase and 

 hypersthene with a considerable amount of magnetite, also occur. 



The anorthosite containing the famous labradorite of Paul Island 

 and the adjacent islands, and parts of the mainland, is of the same 

 age as the granite gneisses. 



Following these are thick beds of sedimentary rocks noAv metamor- 

 phosed, which have been paralleled with the Grenville series of 

 Ontario, though crystalline limestone, the typical rock of the Gren- 

 ville series, occurs only sparingly. The gneisses are usually gar- 

 netiferous. Many of the gneisses are so siliceous that they may with 

 equal propriety be called garnetiferous quartzites. Feldspars are 

 only occasionally recognizable. 



The garnets seem to be of more than one variety, ranging from 

 pale rosy crystals in the more quartzose rocks to dark brownish red 

 varieties in the more basic rocks. 



Graphite is abundant. 



A later sedimentary series, probably 8,000 feet thick, comes above 

 the Grenville series. All these lower beds are pierced by innumer- 

 able black dikes, some up to 100 yards in width. These dikes are 

 of ophitic dolerite, but usually much weathered. 



Above these more ancient rocks, pierced by the dikes, come other 

 thick beds of sediment now converted into slates, with occasional 

 sandstone and breccias; impure dolomite with a layer of amphib- 

 olite. This is the Ramah series. 



The Mugford series, also sedimentary, come above the Ramah and 

 consists of dark slate, chert, quartzite and sandstone and limestone, 

 altogether about 900 feet thick. These contain basic eruptives, tuffs, 

 and agglomerates. 



