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GEOLOGY OF THE TORONTO REGION

 

all crystalline rocks of eruptive origin, the dark green diorite or gabbro or hornblende schist being earlier than the flesh-colored granite and gneiss. The schistose cleavage generally to be observed in these rocks has a steep dip in most cases, and when traced for a distance tends to sweep as wide curves. The mapping of a considerable area usually shows that the granite masses are oval in shape and pass out-wards into gneiss, the quartz and feldspar and mica taking on a parallel arrangement; while the greenschists and other rocks are apt to be squeezed into synclinal bands between the oval gneissoid masses. This is the arrangement characteristic of the batholithic type of mountain structure, and the present surface of hummocky hills displays a cross section through the base of former batholithic domes, long ago carved down to mere stumps.

Near Parry Sound rocks of the Grenville series, mica schists and fine-grained gneisses with crystalline limestone or marble, have been caught in the mountain-building process and are found in long bands between the elongated domes of granite and gneiss. In all_cases the metamorphosed sediments just mentioned, and the green eruptives which have been upheaved by the ascending granite of the domes, are the oldest rocks. They formed the cold and solid crust which was invaded by the molten granite.

The later members of the Archaean, such as the Huronian, have not been found in the region within 100 or 150 miles of Lake Ontario, and the next for-

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