LOGAN ON THE ORIGINAL HURONIAN. 387 
Feet. 
4, Slate conglomerate, composed of pebbles of gneiss and syenite held in an 
argillo-arenaceous cement of a gray or more frequently of a greenish 
color, the latter arising apparently from the presence of chlorite. The 
pebbles, which are of reddish and gray colors, vary greatly in size, being 
sometimes no larger than swan-shot, and at others bowlders rather 
than pebbles, measuring upwards of a foot in diameter; the propor- 
tions of these also vary much; they sometimes constitute nearly the 
whole mass of the rock, leaving but few interstices for the matrix, and 
sometimes on the contrary, they are so sparingly disseminated through 
considerable masses of the matrix as to leave spaces of several feet 
between neighboring pebbles, which may be still several inches in dia- 
meter; with the pebbles of gneiss and syenite are occasionally asso- 
ciated some of different colored jaspers and others of quartz. The 
matrix appears to pass on the one hand into a gray quartzite by an 
increased proportion of the arenaceous grains, and on the other into a 
thin bedded, dark greenish, fine grained slate, which is sometimes 
very chloritic. A third form assumed by the matrix is one in which it 
is scarcely distinguishable from fine grained greenstone. In the slate 
the stratification is often marked by slight differences of color, in the 
direction of which it is occasionally cleavable; the bands in other in- 
stances are firmly soldered together, but in both cases joints usually 
prevail, dividing the rock into rhomboidal forms which are sometimes 
very perfect. Very heavy masses of greenstone are generally inter- 
stratified in the rock, which do not seem confined to any one strat- 
igraphical place,...... -----------------2 eer cc eter ert ste see 2,280 
5. Limestone, usually of a compact texture, but sometimes partially granular ; 
° the colors are green, drab, and dark gray, the latter two prevailing. 
Some beds are occasionally met with of a dull white, with a waxy luster 
in fresh fractures; these weather to a yellowish-brown on the exterior, 
and appear to be dolomitic. The whole band is in general thin bedded, 
and a diversity of character in the layers, probably arising from the 
presence of more or less siliceous matter, causes the surface of the 
weathered blocks to present a set of bold but minute ribs of various 
thicknesses, which when the beds are much affected, as they often are 
by diminutive undulations, contortions, and dislocations, exhibit on a 
small scale a beautiful representation of almost all the accidents that 
oceur in stratification, affording very excellent ready-made geological 
S102 5 DIS pc eS IA I peel asin telcos Cir oa 300 
6. Slate conglomerate of the same general character as that beneath the lime- 
stone, but the pebbles are not so large; it is interstratified with beds 
of reddish and gray quartzite and layers of fine grained, greenish-black 
and light olive-green siliceous slate, some of which yield hones of a 
very fine description ; considerable masses of greenstone are inter- 
stratified in various parts of the deposit,..-------- Ba dig III 3, 000 
