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



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

 Laurentian apatite, it presents a perfectly crystalline texture, while 

 the containing strata are highly metamorphosed ; and this appears 

 to be its general condition wherever it has been examined. Nume- 

 rous slices of the more compact apatite of the beds have been 

 prepared by Mr. Weston, of the Geological Survey ; but, as might 

 be expected, they show no trace of organic structure. All direct 

 evidence for the organic origin of this substance is therefore still 

 wanting. There are, however, certain considerations, based on its 

 mode of occurrence, which may be considered to afford some indirect 

 testimony. 



If, with Hunt, we regard the iron ores of the Laurentian as 

 organic in origin, the apatite which occurs in them may reasonably 

 be supposed to be of the same character with the phosphatic matter 

 which contaminates the fossiliferous iron ores of the Silurian and 

 Devonian, and which is manifestly derived from the included 

 organic remains. 



If we consider the evidence of Eozoon sufficient to establish the 

 organic origin, in part at least, of the Laurentian limestones, we 

 may suppose the disseminated crystals of apatite to represent copro- 

 litic masses or the debris of phosphatic shells and crusts, the structure 

 of which may have been obliterated by concretionary action and 

 metamorphism. 



Such Silurian beds of compact and concretionary apatite (without 

 structure, yet manifestly of organic origin) as that described by 

 Mr. Davies in the 'Journal' of this Society, may be taken as fair 

 representatives of the bedded apatite of the Laurentian. Further, 

 the presence of graphite in association with the apatite in both cases 

 may not be an accidental circumstance, but may depend in both on 

 the association of carbonaceous organisms, whether vegetable or 

 animal. 



Again, the linguliferous sandstone of the Acadian group is a 

 material which, by metamorphism, might readily afford a pyroxenite 

 with layers of apatite like those which occur in the Laurentian. 



The probability of the animal origin of the Laurentian apatite Is 

 perhaps further strengthened by the prevalence of animals with 

 phosphatic crusts and skeletons in the Primordial age, giving a 

 presumption that in the still earlier Laurentian a similar preference 

 for phosphatic matter may have existed, and, perhaps, may have 

 extended to still lower forms of life, just as the appropriation in 

 more modern times of phosphate of lime by the higher animals for 

 their bones seems to have been accompanied by a diminution of its 

 use in animals of lower grade. 



The Laurentian apatite pretty constantly contains a small per- 

 centage of calcium fluoride ; and this salt also occurs in bones, more 

 especially in certain fossil bones. This may in both cases be a 

 chemical accident ; but it supplies an additional coincidence. 



In the lowest portions of the Lower Laurentian no organic remains 

 have yet been detected ; and these beds are also poor in phosphates. 

 The horizon of special prevalence of Eozoon is the Grenville band of 



