LOGAN ON THE ORIGINAL HURONIAN, 389 
Of the interstratified greenstone flows of the above series, Logan 
says:? 
The igneous rocks which, as overflows, it will be convenient to consider constitu- 
ent parts of the stratified series, may be classed as a whole under the denomination 
of greenstone or diorite. The masses are sometimes very great, and in such cases the 
rock usually consists of a greenish-white feldspar, and dark green or black horn- 
blende. The feldspar is sometimes however tinged with red, and the diorite then 
appears to pass into syenite by the addition of a sparing amount of quartz. These 
two forms of the diorite are almost always highly crystalline, and in general not very 
fine grained. Sometimes, however, the greenstone displays a fine texture, and in such 
cases a large amount of it, more particularly in the lower part of the series, frequently 
holds much disseminated chlorite, giving a very decided green color. Portions of it 
are found containing so great a proportion of this mineral as to yield with facility to 
the knife, affording to the aborigines an excellent material for the manufacture of their 
calumets or tobacco-pipes. In addition to the chlorite, epidote is a prevailing mineral 
in this description of rock, associated with which an amygdaloid, already alluded to, 
is in one place seen, some of the cellules of which contain quartz, others calespar and 
bitterspar, and some few of specular iron. The amygdaloidal trap is very distinctly 
arranged in layers, which, though they do not exceed two or three in number, give, 
with beds of porphyritic greenstone containing large crystals of feldspars, occurring 
near the amygdaloid, a stratified aspect to the whole of the mass of the trap associated 
with them. No such decided appearances of stratification have been met with in the 
more crystalline greenstones. They usually, however, display parallel planes of divis- 
ion in several directions, and it frequently happens that some of these parallel planes 
are only moderately inclined; but there have not been observed on the surfaces or-in 
the character of the rock any distinct evidences of stratification or of successive 
deposit, and no columnar structure at right angles to any set of planes such as some- 
times so clearly marks an overflow. It is therefore, in most instances, only by a refer- 
ence to its immediate relation to the sedimentary rocks on each side that the general 
attitude of any band of the greenstone can be made out. 
Independent of the overflows, igneous rocks are connected with the formation in 
intrusive masses. These intrusive masses consist of greenstone and granite. The 
intrusive greenstones do not seem to differ much in mineral character from those 
composing the overflows: they constitute dikes which run in so many directions that 
it is difficult to determine the prevailing ones. These dikes vary in breadth from a 
few inches to several hundred feet; they cut all the stratified rocks of the series, 
igneous as well as sedimentary, splitting into branches which often join one another 
and inclose great fragments and masses of strata. The intrusive granite, in so far as 
observed, is in general of a decided red color, arising from the presence of a largely 
preponderating quantity of red feldspar, which is mingled with translucent white 
quartz: mica is not very abundant, and hornblende sometimes accompanies or replaces 
it. -From large masses of the rock however both these minerals are often wholly 
absent, but epidote in general forms a constituent, sometimes in great abundance. 
1 Geology of Canada, 1863, p. 57. 
