168 THE CANADIAN NATURALIST. [Vol. viiL 



explorations of the Canadian Survey, in the districts of Burgess 

 and Elmsley, which are especially rich in apatite, that the 

 mineral occurs largely in beds interstratified with the other mem- 

 bers of the series, though deposits of the nature of veins likewise 

 occur. It also appears that the principal beds are confined to cer- 

 tain horizons in the upper part of the Lower Laurentian, above 

 the limestones containing Eozoon, though some less important 

 deposits occur in lower positions. * 



The principal apatite-bearing band of the Laurentian consists 

 of beds of gneiss, limestone, and pyroxene-rock, and has a thick- 

 ness of from 2G00 to 3600 feet. It has been traced over a great 

 extent of country west of the Ottawa river, and has also been 

 recognized on the east side of that river as well. The mineral 

 often forms compact beds with little foreign intermixture ; and 

 these sometimes attain a thickness of several feet, though it has 

 been observed that their thickness is variable in tracing them 

 along their outcorps. Several beds often lie near to each other 

 in the same member of the series. Thin layers of apatite also 

 occur in the lines of bedding of the pyroxene-rock. In other 

 cases disseminated crystals are found throughout thick beds of 

 limestone, sometimes, according to Dr. Hunt, amounting to two 

 or three per cent, of the whole mass. Disseminated crystals also 

 occur in some of the beds of magnetite, a mode of occurrence 

 which, according to Dr. Hunt, has also been observed in Sweden 

 and in New York in the Laurentian magnetites of those regions. 

 The veins of apatite fill narrow and usually irregular fissures ; 

 and the mineral is associated in these veins with calcite and with 

 large crystals of mica. In one instance, at Ticonderoga, in New 

 York, the apatite, instead of its usual crystalline coudition, as- 

 sumes the form of radiating and botryoidal masses, constituting 

 the Eupyrchroite of Emmons. Since these veins are found prin- 

 cipally in the same members of the series in which the beds 

 occur, it is a fair inference that the former are a secondary for- 

 mation, dependent on the original deposition of apatite in the 

 latter, which must belong to the time when the gneisses and 

 limestones were laid down as sediments and organic accumula- 

 tions. 



In all the localities in which I have been able to examine the 

 Laurentian apatite, it presents a perfectly crystalline texture, 



* Vcnnor's Reports, 1872-73 and 1873-74. 





