440 A POPULAR EXPOSITION OF THE 
limestones are of all geological ages. Some limestones, again, are of 
an earthy texture: the well-known chalk of Europe is an example ; 
also our own “ calcareous tufa,”’ or “shell marl.” Many of the dark 
limestones, as those of Niagara, &c., are more or less bituminous. 
All effervesce in acids; but the dolomites produce merely a feeble 
effervesence unless the acid be heated. Limestones which contain 
from 15 to 25 per cent. of argillaceous matter in intimate admixture, 
yield hydraulic or water lime. Beds of this kind occur at Thorold, — 
Cayuga, Loughboro’, Kingston, Hull, Quebec, and other localities. 
(See Parr V.) 
Conglomerates consist of rounded stones or masses of quartz, sand- 
stone, &c., cemented together, or imbedded in a paste of finer sand- 
stone, limestone, or other rock substance. The imbedded masses are 
sometimes of great size, a fine example of which may be seen at 
Quebec. Conglomerates, both altered and unaltered, are abundant 
amongst the Huronian rocks. 
Breccias consist of angular masses or fragments of rock, cemented 
together, chiefly of some kind of limestone. Whilst conglomerates 
frequently consist of materials brought from a greater or less dis- 
tance, true breccias are necessarily formed in place. Examples of 
calcareous breccias occur in the Eastern Townships. Also with im- 
bedded trap and slate fragments, near the Bruce Mines, Lake Huron, 
and elsewhere. — 
(2) Formation of Sedimentary Rocks.—-The manner in which the 
ordinary sedimentary rocks, sandstones, shales, &c., have been formed, 
or built up as it were, is rendered clear by the observation of certain 
natural processes still in action. We find for example, at the present 
day, that sediments of various kinds are constantly being carried down 
by streams and rivers into lakes and seas, and are there deposited. 
We find, moreover, that the cliffs of many sea (and lake) coasts are 
bemg continually abraded and washed away by the action of the 
waves. Observation shews also, that the sedimentary matters thus 
obtained, are always deposited or arranged in regular layers or beds, 
and that they frequently enclose shells and sea-weeds, together with 
bones and leaves, drifted from the land, and other organic bodies. 
Hence it is now universally admitted, that, with the exception of cer- 
tain limestones and dolomites, beds of rock-salt, gypsum, coal, and 
other chemical or organic deposits of small extent, all the sedimentary 
rocks have been formed directly out of previous!y-existing rock-masses, 
