QUEBEC GROUP IN GEOLOGY. 13 
to be of Trenton age. From Danville south-westward the course of the dislocation has been 
traced, and it fully explains several intricate points in connection with the distribution of 
the formations. North-eastward its course is still doubtful, but I believe it will be found 
to explain a circumstance described, page 241, Geology of Canada, where Sir William says : 
“In the general synclinal form that lies between the overlap and the Bayer and Stanbridge 
anticlinal, the Quebec Group is either completely or very nearly divided into two areas by 
the “underlying black slates, on or near the St. Francis.” The cause of this was, however, 
not then understood, because the position of the black slates referred to was supposed to be 
below instead of aboye the Quebec Group, and the great Potton and Danville fault had not 
been discovered. 
The points, then, which in the foregoing remarks I have endeavored to establish are : 
Ist. That the Quebee Group of Logan consists of rocks belonging to at least three distinct 
systems: Pre-Cambrian, Cambrian and Cambro-Silurian. 2nd. That the lower group 
presents generally a simple anticlinal structure, while the newer group is spread out in 
a crumpled and folded synclinal form, resting on and against the north-western flank 
of the older group, and presenting within itself many intricate details of distribution 
caused by original unconformities and overlaps, and by subsequent folding and fault- 
ing, all but the last of which are illustrated in a modified form in the comparatively 
undisturbed lower Paleozoic region north-east of the St. Lawrence and Champlain fault. 
3. That much of this material composing the rocks of the upper part of the lower 
groups is of contemporaneous, irruptive and eruptive origin; though, for the most part, 
through cleavage and alteration so changed in external physical characters as to cause 
these rocks to be classed as “metamorphic in origin,”’—notwithstanding that they still 
closely correspond in chemical composition with recognized igneous and volcanic rocks, and 
differ essentially from any known ordinary unmixed sedimentary deposits. And it must be 
borne in mind, in considering the origin of those ancient rocks, that neither their elastic 
character nor their laminated or bedded structure is sufficient, either together or alone, to 
determine that they have had a purely sedimentary origin, but must be studied in connec- 
tion with their mineralogical and geognostical relations, the latter being by far the most 
important, because all other characters are possessed in common by both classes, and there- 
fore, especially when studied, as is too often the case, only in the laboratory, are of little or 
no value as evidence for or against the respective theories of origin. 
