On Metallic Minerals. 387 



composed of a very friable limestone, often of so crystalline 

 a structure as to resemble calcareous spar. It often contains 

 specks of graphite, and sometimes parts of it are discoloured 

 by what appears to be the green carbonate of copper. Its 

 colours are whitish, yellowish, and reddish. Similar 

 aggregates have been met with in sinking the lock pits on 

 the line of the Ridcau Canal, and in one instance it has 

 been observed to have a geological position below the red 

 sandstone. 



This limestone is perfectly useless as a building material, 

 and for lime it would not answer well, because it flies and 

 falls to pieces and powder in the kiln. When the lime is 

 recjuircd for immediate use, it might answer, but the 

 quickness with which it would pass from a caustic lime to a 

 carbonate, would render delay destructive of its j)ower of 

 fixing in a state of mortar, Mr. M'Donald, the obliging 

 proprietor of the n)ills, procures all the lime he is in want 

 of from Kingston. 



About one mile from the mouth of the Gannanoqui the 

 navigable portion of it begins, and continues as far as the 

 ** marble rock or falls," a distance of about ten or twelve 

 miles.* As the geological features of this part of the river 

 are interesting, 1 shall endeavour to give some account of 

 them. 



The waters of the Gannanoqui have here apparently 

 forced a contracted passage through a hill of rock, leaving 

 a section on either side, varying from twenty to fifty feet 

 above the river. On the left bank this section is through 

 talcose schist and serpentine, — on the right it is through 

 marble. Granite also on the left bank is seen forming n 



* About fire iiiilr* l>) luiid. 



