ABSTRACTS 93 



The Grenville series differs from the Fundamental Gneiss in that 

 it contains certain rocks whose composition marks them as highly- 

 altered sediments. These rocks are in part limestones and in part 

 certain peculiar gneisses, rich in sillimanite and garnet, having the 

 composition of shales, or very rich in quartz and passing into quart- 

 zite, having thus the composition of sandstones. These rocks, as has 

 been shown in one of the papers above referred to, usually occur in 

 close association with one another, and are quite different in composi- 

 tion from any igneous rocks hitherto described. These rocks it is 

 which are considered as characterizing the Grenville series. They 

 usually, however, form but a very small proportion of the rocky com- 

 plex of the areas in which they occur, and which, owing to their pres- 

 ence, are referred to the Grenville series. They are associated with, 

 and often enclosed by, much greater volumes of gneisses and amphi- 

 bolitic rocks, identical in character with those of the Fundamental 

 Gneiss. The limestones are also almost invariably penetrated by great 

 masses of coarse pegmatite, and in some cases large bodies of the 

 limestone are found imbedded in what would otherwise be supposed 

 to be the Fundamental Gneiss. The whole thus presents the character 

 of a series of sedimentary rocks, chiefly limestones invaded by great 

 masses of the Fundamental Gneiss, and in which possibly some varie- 

 ties of the gneisses present may owe their origin to a partial admixture 

 of sedimentary material with the igneous rocks by actual fusion. There 

 is, however, no reason to believe, from the evidence at present avail- 

 able, that any considerable proportion of the series has originated in 

 the last mentioned manner. 



From the relations of the several series, as displayed in central 

 Ontario, it is believed that the sedimentary portion of the Grenville 

 series is but a modified part of the Hastings series, that in fact the 

 present relations of the Grenville series are due to a commingling of 

 portions of the Hastings series with the Fundamental Gneiss along 

 their line or zone of contact. The Fundamental Gneiss upon which 

 the Hastings series was originally laid down having at a subsequent 

 time been softened by the influence of heat, and having under the 

 influence of dynamic action eaten into and fretted away the overlying 

 Hastings series, giving rise to an intermediate zone of mixed rocks 

 which constitutes the Grenville series. The relations of the two series 

 being thus very similar to that shown by Lawson and Barlow to exist 

 between the Huronian and the Fundamental Gneiss in the districts 

 about Lake Superior and Lake Huron. 



