MINERALS AND GEOLOGY OF CANADA. 201 
Fig. 196 a.=[llenus crassicauda Fig. 197.—Ceraurus pleurexanthemus 
(Hall). (Green). 
Some of the limestones of the Trenton Group are sufficiently fine- 
grained to take a good polish, and hence to be employed as marble. 
To these belong, more especially, a dark or chocolate-brown variety 
from the River Mississippi in the township of Pakenham (Lanark 
Co.), and grey varieties from the township of Gloucester (Carleton 
Co.), and from Montreal. Good building stones are quarried in La 
Chevrotiére (the so-called Deschambault stone, of which the principal 
buildings in Quebec are constructed), at Montreal, Point Claire, 
Mille Roches in Cornwall township, Kingston, Ox Point near Belle- 
ville, Cobourg, Lake Conchiching north of Lake Simcoe, and various 
other localities. The Lake Conchiching stone is highly silicious, 
and consequently difficult to dress, although exceedingly durable. 
Excellent lime is also obtained from most of the limestones of this. 
group. A thin light-coloured bed belonging to the lower part of the 
series, and which may be traced with slight interruption from Mar- 
mora to Lake St. John in the township of Rama, yields also a litho- 
graphic stone of useful quality. Near the mouth of the Coldwater 
River on Georgian Bay, likewise, a thin greenish sandstone, quite at 
the base of the series, has been long used by the Indians for the 
manufacture of pipe-bowls, &c. It is easily worked at first, being 
comparatively soft until after exposure for some time to the atmos- 
phere. 
The limestones of the Trenton Group are extensively developed in 
both Western and Eastern Canada. In the former (see the Map, 
fig. 249, in which this group is denoted by the number 6), they occur 
largely in the counties of Prescott, Russell, Carleton, Renfrew, 
Lanark, &c., between the Ottawa and the St. Lawrence, and espe- 
Vou. VIII. Q 
