No. 3. J DAWSON — PHOSPHATES OF CANADA. 167 



ascertained that these shells also contain calcic phosphate in con- 

 siderable proportion. The proportion of this substance in a shell 

 not quite freed from matrix was 2-09 per cent. These shells 

 have usually been regarded as Pteropods ; but I find that the 

 Canadian primordial species show a structure very different from 

 that of this group. They are much thicker than the shells of 

 proper Pteropods ; and the outer layer of shell is perforated with 

 round pores, which in one species are arranged in vertical rows. 

 The inner layer, which is usually very thin, is imperforate. In 

 one species (I believe, the It. americanus of Billings), the per- 

 forations resemble in size and appearance those in the shells of 

 TerebratulcB. In another species (//. micans probably) they are 

 very fine and close together, as in some shells of tubicolous worms. 

 I am therefore disposed to regard the claim of these shells to the 

 rank of Pteropods as very doubtful. They may be tubicolous 

 worms, or even some peculiar and abuormal type of Brachiopod. 

 In connection with this last view, it may be remarked that the 

 operculum of some of the species much resembles a valve of a 

 Brachiopod, and that the conical tube is in some of them not a 

 much greater exaggeration of the ventral valve of one of these shells 



r> do 



than the peculiar Calceolu of the Upper Silurian and Devonian, 

 which has been regarded by some palaeontologists as a true Bra- 

 chiopod. I have not, however, had any opportunity of comparing 

 the intimate structure of CalceoJa with that of these shells. 

 Shells of Hyolithes occur in the Lower Potsdam in the same beds 

 with the phosphatic nodules; and in one of these Mr. Weston 

 has found a series of conical shells of Hyolithes pressed one within 

 another, us 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 in- 

 credible that carnivorous animals feeding on them should pro- 

 duce phosphatic coprolites than that this should occur in the 

 case of more modern animals feeding on fishes and other verte- 

 brates. 



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

 abundant 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 

 Vol. VIII. K No. 3. 



