GNEISSIC FOLIATION. 127 



which may, therefore, be properly said to be allied to it; and another 

 which crosses the strike of the lamination and seems to have been 

 developed in the rock as a species of fine jointing after its assump- 

 tion of a hard solid state. Both kinds may often be seen cleaving 

 the same rock, but only the former will now be considered briefly, as 

 it is that which prevails in the upper or schistose portion of the 

 archean system. That such a schistose cleavage may be developed in 

 igneous rocks is shown by its occurrence in intrusive dykes. It is 

 not, however, only under the conditions in which dykes occur that 

 this cleavage may be developed in igneous rocks, for on a larger scale 

 I have repeatedly observed pei'fectly massive and homogeneously 

 textured rocks of a diabasic or dioi'itic composition merge into a 

 schistose vai'iety of the same composition and aspect, without a break 

 to create a doubt as to the identity of origin of both. Further, I 

 have noticed that even granite, which is unmistakably intrusive, may 

 exhibit a rough but quite well-marked schistose fracture. This is 

 well seen on the northern skirts of the Echo Bay (Lake of the Woods) 

 intrusive mass of granite, which breaks through a diabasic rock, and 

 near its contact with the latter becomes less coarsely granular and 

 roughly schistose. 



If, then, a schistose cleavage may be developed in a truly igneous- 

 rock, the mere fact that the higher portions of the archean system 

 are characterized by such a schistose cleavage, even though it be 

 parallel for the most part with the stratiform arrangement or bedding 

 of the rocks, is no reason whatever in support of the belief that these 

 rocks were once aqueous sediments. 



In answer to a question of Mr. Rouse respecting the expan- 

 sion of rocks in cooling. Dr. Ellis referred to a number of 

 substances that expand in the act of solidifying, and entered 

 into an explanation as to the cause of the expansion in such 

 cases. 



Mr. T. Nelson Dale stated that the views of the paper 

 agreed with those of Professor Hitchcock, the State Geologist 

 of New Hampshire, who regarded large masses of gneiss in the 

 White Mountains as of igneous origin, but that there were 

 cases where gneiss was undoubtedly of metamorphic origin ; 

 thus Beudant, one of the old French geologists, cites a case of 



