ANALYTICAL ABSTRACTS. 30/ 



clase. The upper division of the Laurentian is more complex. It possesses 

 more regularity in stratification and includes great banded masses of crystal- 

 line limestones, vitreous quartzites, mica-schist and hornblende-schist, massive 

 pyroxene, and massive and foliated labradorite rocks. Considerable areas of 

 granite and syenite occur in the formation. The Upper Laurentian of the 

 Ottawa valley may be roughly estimated to be at from 50,000 to 100,000 feet 

 in thickness. 



While the older Laurentian rocks afford no proof »f the permanent exist- 

 ence of the sea upon the earth, water appears to have been present, perhaps 

 only as precipitations upon the surface, at every stage of its formation. But 

 the deposits of limestone and tolerably pure silica in distinct bands in the 

 Upper Laurentian afford strong support to the aqueous theory of its depo- 

 sition. 



With the beginning of the Huronian period great volcanic activity began, 

 and there is evidence of the permanent abode of water on the surface of the 

 earth. The general character of the Huronian rocks may be said to be 

 pyroclastic, by this signifying that, although fragmental, they have neverthe- 

 less had an igneous origin. 



The area mapped between the Huronian belt and the shore of Georgian 

 bay appears to belong to the Upper Laurentian. The rocks are gneisses of 

 the typical Laurentian varieties, finely stratified and regularly arranged in 

 anticlinal and synclinal folds, the angles of dip usually not being far from 

 forty-five degrees, but lesser and greater dips being found. Red and gray 

 varieties are about in equal proportion, and they alternate with each other in 

 thick and thin sheets. Mica-gneisses are predominant. No beds of crystal- 

 line limestone are found west of Iron Island in Lake Nipissing. Limestones 

 are associated with the gneisses on some of the islands of the eastern part of 

 this lake and at Lake Talon on the Mattawa. In the Parry Sound district 

 are five distinct bands of Laurentian limestone. These rocks are classified 

 with the Upper Laurentian rocks of the counties of Ottawa and Argenteuil. 



The Laurentian rocks northwest of the Huronian belt are heavy contorted 

 gneisses of the lower Laurentian. Associated with the gneisses are red gran- 

 ites which are classed with the Laurentian, but which may be really Huronian. 

 These may have formed by softening the gneiss by heat, combined with 

 re-crystallization, or they maybe due to the alteration of the Huronian arkoses 

 or graywackes, or they may be mainly eruptive. These granites are along the 

 contact line between the Laurentian and Huronian. Along the line of contact 

 between the granites and Huronian quartzites and schists, the rocks are much 

 broken. It is not improbable that a fault exists at the line of junction between 

 the Laurentian and Huronian rocks. 



The great Huronian belt consists of a great variety of rocks, such as 

 crystalline schists, quartzites, conglomerates, agglomerates, clay-slates, green- 

 stones, dolomites, etc., the majority of which are pyroclastic. The rocks are 



