J. W. DAWSON ON THE PHOSPHATES OF CANADA. 289 



of Hyolithes pressed one within another, as if they had passed in an 

 entire state through the intestine of the animal which produced the 

 coprolite. 



Inasmuch, then, as some of the most common invertebrates of 

 the Cambrian seas secreted phosphatic shells, it is not more incredible 

 that carnivorous animals feeding on them should produce phosphatic 

 coprolites than that this should occur in the case of more modern 

 animals feeding on fishes and other vertebrates. 



We may now turn to the question as to the source of the abun- 

 dant apatite of the Laurentian rocks. Were this diffused uniformly 

 through the beds of this great system, or collected merely in fissure 

 or segregation veins, it might be regarded as having no connexion 

 with other than merely mineral causes of deposit. It appears, 

 however, from the careful stratigraphical explorations of the Cana- 

 dian Survey, in the districts of Burgess and Elmsley, which are 

 especially rich in apatite, that the mineral occurs largely in beds 

 interstratined with the other members of the series, though deposits 

 of the nature of veins likewise occur. It also appears that the 

 principal beds are confined to certain 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 thickness of 

 from 2600 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 outcrops. 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 condition, assumes 

 the form of radiating and botryoidal masses, constituting the Eupyr- 

 chroite of Emmons. Since these veins are found principally in the 

 same members of the series in which the beds occur, it is a fair 

 inference that the former are a secondary formation, 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 accumulations. 



* Vennor's Reports, 1872-73 & 1873-74. 



