79° 



W. G. FOYE 



however, would not explain a phenomenon such as that shown by 

 the dike just described (Fig. 2). It is believed that the fissility 

 which allowed the granite to intrude the sediments and the gneissic 

 structure of these granites were both results of a persistent force, 

 the static pressure of the overlying sediments. The Grenville 

 series is said by Adams and Barlow to be approximately 50,000 

 feet thick. This series compares with the Shuswap Terrane which 

 is 30,000 feet thick. 



The elongation or compression of the amphibolitic layers and 

 the presence of amphibolitic inclusions may be explained as easily 



by the theory of Daly and 

 Fenner as by that of Adams. 

 The granitic gases and fluids 

 must have had their origin at 

 certain definite points. At these 

 points they were pushed upward 

 and sideways along planes of 

 easy parting and a pine-tree 

 structure was produced. In 

 general, the increase of material 

 due to the addition of granite 

 would produce a doming at the 

 center of intrusion with qua- 

 quaversal dips away from these 

 points. However, the subsidence of the magma on cooling might 

 very possibly cause a collapse of the dome and irregular dips 

 would result. 



The mechanism of lit-par-lit intrusion, as explained by Fenner, 1 

 is dependent on the fluxing power of the pneumatolytic gases given 

 off by the granite. These go before and prepare the way for the 

 later intrusion of the granite magma. The prevalence of lit-par- 

 lit rather than batholithic intrusions in pre-Cambrian terranes 

 may be due, therefore, to the greater abundance of magmatic gases 

 in the earlier periods of the earth's history. The vast amounts of 

 pegmatitic granite associated with pre-Cambrian areas lends 

 support to this theory. 



1 Journal of Geology, XXII (1914), PP- 5942- 



Fig. 2. — A vertical dike showing hori- 

 zontal schistose structure. 



