484 R. W. ELLS — MICA DEPOSITS OF THE OTTAWA DISTRICT. 



local causes, easily recognized, the strike of the pyroxene, quartz -felspar, 

 and other dike-like intrusions, is often nearly at right angles to this, but 

 sometimes varying from it to apparent conformity with the bedding of the 

 stratified rocks. The dip of the gneiss changes frequently from the east 

 to the west, so that over a section of hundreds of miles in extent the 

 whole series is found to be in a succession of folds, often closely placed 

 with regularly occurring anticlinals and synclinals, which structure is, 

 moreover, wonderfully confused by the occurrence of numerous faults 

 and overturns. 



Occurrence of Apatite and Mica. — It has been already pointed out in a 

 previous paper * that the deposits of apatite are confined entirely to the 

 pyroxene dikes of this system, and that the mineral occurs for the most 

 part near the contact of these dikes with the gneiss or near the intersec- 

 tion of cross-dikes of intrusive dolerite or felspar. The occurrence of 

 mica in these rocks presents almost identically similar conditions to the 

 apatite as regards its presence in workable quantity, but differs in this 

 respect, that while the apatite is found exclusively in pyroxenic rocks, 

 the mica is often associated with other kinds of intrusives. It is, how- 

 ever, more particularly found in two varieties, namely, the pyroxene 

 which varies greatly in color and hardness, and in a coarse admixture of 

 clear quartz and grayish felspar, which is generally styled a pegmatite, 

 and which contains also crystals of tourmaline, garnet, etcetera. This 

 quartz-felspar rock differs, however, very greatly from the usual varieties 

 of pegmatite found in the Laurentian, which is usually very much finer- 

 grained, and occurs generally as veins intersecting the gneiss as one ap- 

 proaches the great masses of anorthosite or gabbro. The quartz-felspar 

 those of pyroxene, frequently cut the gneiss along the line of strike of 

 dikes, like the latter, but its intrusive character is clearly evidenced in 

 most cases by the sending off of spurs into the mass of the gneiss in con- 

 tact, as well as by the fact that it frequently cuts directly across the gneiss 

 and intersects the pyroxene as well, thus showing it to be a later intrusion. 

 Inclusions of the grayish or reddish gneiss which is penetrated by these 

 rocks are also frequently found caught in the mass, both of the pyroxene 

 andfel spar, and furnish further evidence of the intrusive character of these 

 rocks. In some places the presence of three distinctly intrusive dikes is 

 recognized in the same opening, the oldest being the p3''roxene, the 

 second, cutting the pyroxene, is a quartz-felspar, and the third is a black 

 trappean rock. 



It has been stated by some writers that the apatite and mica occur in 

 the Laurentian limestone, as well as in the gneiss and pyroxene. This 



* Canadian Mining Review, Ottawa, March, 1893. 



