124 A POPULAR EXPOSITION OF THE 
&c.,—the latter constituting the variety known as jasper. The slates 
and slate conglomerates appear to owe their general green colour to 
the presence of chlorite and epidote, or perhaps more commonly to the 
former alone. In some, different shades of green (or of green, black, 
and red) run in parallel lines, imparting to the rock a beautiful riband- 
ed aspect. Well-marked slaty cleavage, however, is apparently very 
rare: if ever present. In the conglomerates, the enclosed pebbles, or 
rounded fragments, for some are eight or ten inches across, consist of — 
pieces of gneiss, syenite, quartz, &c., evidently derived in many 
instances from the adjacent Laurentian rocks. Some of these slates 
and slate conglomerates form vast stratified masses of between two 
and three thousand feet in thickness. The limestone beds of the 
Huronian series are of comparatively subordinate importance. They 
are chiefly of a light or dark grey colour, though in places they offer 
a white, greenish or brownish tint. In structure, they are more or less 
compact, or but slightly crystallme; the latter condition is, however, 
rare. Some exhibit a brecciated appearance, and all seem to contain 
a good deal of siliceous matter. Thin beds of chert (a flinty variety 
of quartz) occur indeed interstratified with them, in some places. In 
addition to their want of crystalline texture, these limestones differ 
from those of the Laurentian series in not containing any crystallized 
minerals—apatite, garnets, tourmaline, homblende, &c.,—a fact point- 
ed out by Professor Sterry Hunt. The masses of greenstone inter- 
stratified with the slates and other beds of this series, are of somewhat 
doubtfui origin. They may consist, as suggested by Prof. Hunt, of 
altered sedimentary deposits; or they may be stratified beds made up 
of materials derived from neighbouring dykes and eruptive greenstone 
masses ; or, otherwise, they may consist of overflows of igneous rock 
during the building up of the associated strata; or of lateral dykes, so 
to say, forced at some after period between the lines of bedding. As 
regards structure, &c., they exhibit several varieties. Some are large- 
grained, consisting of feldspar (usually of a greenish-white color) and 
dark green or black hornblende. Other varieties are fine-grained, and 
of a uniform green colour except when they become amygdaloidal or 
contain cavities filled with cale spar, magnesite, quartz, &c. Certain 
fine-grained varieties also become schistose avd quite sectile, from the 
presence of a large quantity of chlorite. These finer greenstones are 
likewise porphyritic in places, or hold imperfect crystals of feldspar ; 
and those of coarser grain, by the addition of a little quartz, pass 
