1 8 The Ottawa Naturalist. [April 



but as a rule these are of more recent date than the limestone 

 and gneiss with which they are associated ; and it is in 

 connection with these later intrusive masses that, in our search 

 for economic minerals, we areparticularlyinterested,sincein some 

 of these our most important deposits occur, among which may 

 be mentioned the several ores of iron, the gold of Hastings and 

 the nickel of Sudbury. 



The determination of these areas is therefore very important 

 from the economic standpoint, and much time and study has 

 been, and is still being, devoted to the study of this group of 

 rocks by th 2 officers of the Geological Survey. In connection 

 with the upper gneisses also, or rather with the intrusive masses 

 of p}'roxenic rocks associated with these, are the great deposits 

 of apatite, mica, &c. found both to the north and south of the 

 Ottawa River. The asbestus of this district is associated with 

 serpentines and generally with the crystalline limestone, and 

 were it not for the enormous deposits found in the Eastern 

 townships of Quebec, the occurrence of this mineral would be of 

 much greater importance than is now the case. 



For though mineral deposits may theoretically have the 

 same value at different places and times, this value does not 

 always hold in practice. Thus the apatite deposits which were 

 at one timi extensively mined and of great economic 

 importance, have, since the development of the more easily 

 obtained phosphates of the Southern States, become practically 

 valueless, since they cannot now be mined at a figure to enable 

 them to enter into successful competition with the cheaper 

 output of the south. A somewhat similar case is afforded in the 

 micas, though here the results are not so disastrous to the persons 

 engaged in the'^ndustry. At one time the price of this material 

 was governed, to a certain extent, by the size and colour of the 

 crystals obtained, but the market value of the mineral, in regard 

 to the largest sizes, has now greatly diminished, owing to the 

 discovery of a process by which sheets of almost any required size 

 can now be built up from small pieces, by a process of 

 I'nterlamination, cementing and pressure, so that the high prices 

 once obtainable for large crystals cannot at present be realized, 



