598 TRANSACTIONS OF SECTION C. 



It is evident that the invasion of the later Laurentian granites and gneisses 

 was SLCcompanied by very important dynamic and metamorpbic effects. Most of 

 the batholithic domes of North-western Ontario are post-Lower Huronian, and 

 date perhaps from the Middle Huronian or the interval between it and the Upper 

 Huronian (Animikie). 



The granites and gneisses of this second time of mountain building have not 

 been distinguished in mapping from those of the first in most places ; and as they 

 are both of precisely the same habit it will probably never be possible to separate 

 them completely. Thus far both have been included under the name Laurentian, 

 which must be considered as representing a lithological facies rather than a 

 geological period. It may be, however, that the formation of batholithic moun- 

 tains never really ceased from the end of the Keewatin to the end of the Lower 

 Huronian. As the rocks called Laurentian are entirely eruptive, they should not 

 be limited to a definite time, but only to a definite set of conditions as to com- 

 position, Tate of cooling, and amount of pressure. 



As in the earlier cycle, the period of mountain-building was followed by a 

 period of destruction, ending in a peneplain of very wide extent. 



The Animikie or Upper Huronian. 



The interval between the lower formations and the Animikie is of great 

 magnitude, perhaps even greater than that between the Keewatin and the Lower 

 Huronian; and Lawson has suggested for it the name of the Eparchaean Interval. 

 The Animikie has not been found resting on the Middle Huronian in Canada, so 

 that this formation may partly bridge the chasm. Unless the Middle Huronian 

 quartzites include part of the products of erosion we have no evidence as to the 

 disposal of the many thousands of cubic miles of materials removed from the later 

 Laurentian mountains. 



The Animikie begins in most places with a thin basal conglomerate lying 

 almost horizontally on the upturned edges of the previous schists and gneisses. 

 Above this come chert, black slate, and other sediments, sometimes to the extent 

 of 8,000 or 10,000 feet. The slate often contains carbon enough to make an 

 important coal region if collected in definite beds. 



The whole no doubt implies a transgressing sea, which ultimately must have 

 covered a very large part of the Canadian Shield, since rocks of this age are 

 found over wide surfaces north-west of Lake Superior, near Lake Mistassinni, 

 in the heart of Labrador, on the east side of Hudson Bay, and near Great Bear 

 and Dubaunt lakes. These rocks are found in Labrador up to 1,575 feet above the 

 sea. This level, if extended in all directions, would submerge three-fourths of 

 the Archaean peneplain. 



At present these areas, though large, are widely separated ; and it may be 

 rash to assume that even soft, easily weathered rocks, like the Animikie slate, 

 could have been completely removed from the intervening spaces. It is probable, 

 however, that less than half of the Archaean then remained as dry land. 



The Keweenawan. 



There is an interval marked by a sma/11 discordance and a basal conglomerate 

 between the Animikie and the Keweenawan, but the break in time was apparently 

 not great. The two groups of rocks often occur together, though in many places 

 the Keweenawan sediments overlap on to the Archaean, as in the neighbourhood of 

 Lake Nipigon. Most of the Keweenawan sedimentary rocks are of shallow-water 

 varieties, such as sandstone and conglomerate. Atr various places on the north- 

 east shore of Lake Superior a coarse basal conglomerate is found as remnants 

 preserved in small valleys or ravines in the granite. The ancient surface is now 

 in process of resurrection by erosion, and the boulders once rolled on a Keweena- 

 wan shore are being freed from their matrix and once more set in motion by the 

 waves of Lake Superior. 



The Keweenawan, like the Keewatin, was a time of vigorous volcanic activity, 

 and in most places the lava-sheets arid laccolithic sills of diabase connected with 

 their eruption far surpass the sediments in amount. The volcanic rocks are 

 generally basic in character, and probably most of the diabase dykes widely found 

 in almost all parts of the Canadian Archaean are of this age. The important 



