

52 B. N. A. BOUNDARY COMMISSION. 
the conglomerates. The conglomerate rocks, have as a whole much the 
aspect of volcanic breccias, such as those found in association with the 
older Silurian series in Wales and Cumberland; and volcanic action would 
appear to offer the most reasonable explanation of their origin and dis- 
tribution. Their association with the greenstone-like beds, would also then 
be explicable, as the ejection of rock fragments and lapilli, would probably 
be accompanied by the outflow of molten rock in the same neighbourhood; 
or many of these layers may have originally been ash-beds formed of 
the finer detritus from volcanic vents. The material of these, having been 
at one time in a state of fusion, would have the chemical composition 
of hornblende, pyroxene, felspar, &c., and would yield more readily 
to a subsequent metamorphism than the surrounding beds of detritus 
formed by subeerial weathering and transported by water, and from 
which a great part of the basic constituents had been removed. These 
rocks and the conglomerates, which have been united under the dark- 
green colour in the appended general section because of their associa- 
tion, would in this case be properly classed together from their similar 
origin. 
107. A point of difference between the rocks of this series, and those 
of some parts of the typical Huronian of the localities already mentioned, 
is the entire absence of fragments of the underlying granitic and gneissi¢ 
beds in the conglomerates and breccias. Fragments of their reddish 
felspars do not even occur among the quartzites, nor are rocks of reddish 
tints, such as might arise from their disentegration found. This is a 
remarkable fact, and might seem to indicate that the Laurentian had not 
suffered much metamorphism before the formation of these rocks, and 
consequently that they are older than the true Huronian. The appear- 
ance of conformity with the Laurentian, of the rocks of this and other 
similar, but widely separated areas; and their resemblance to some rocks 
deseribed as Laurentian in Hastings County, and elsewhere, would 
appear to point in the same direction. * 
108. The absence of altered Laurentian rocks in the composition of this 
series may, however, be supposed to show that their formation took place 
at a period subsequent to that of the typical Huronian, but before the vio- 
lent disturbances which brought large areas of Laurentian again under the 
influence of denudation ; and that their material was almost wholly de- 
“ *Sce on the latter point, Geol. Canada., p. 31. Report of Progress Geol. Surv. Canada. 1866, p. 91, et 
seqg., and foot note to p, 93 ; also 1866-69, p, 143, et seq. 

