I IT 



li 



60 



Canadian Record of Scietice. 



I 



'iil! 



ing since they throw much fresh light on the charac- 

 ter of the oarlient known forms of these organisms, and 

 their discovery is tho more opportune from the fact that 

 oar knowledge of the existing hexactinellid sponges — the 

 group to which all, or nearly all, these fossils belong — 

 has been vastly increased by the work of Prof F. E. 

 Schulsie, of Berlin, on the hoxactinelled sponges dredged up 

 by the Challenger expedition, and thus we ave now better 

 enabled than hitherto to compare the fossil and the recent 

 forms. 



Sir J. W. Dawson has already given a preliminary account 

 of the character and bliratigraphical relations of the rock 

 in which the sponges occur, as well as some details of the 

 fossils themselves, and at his invitation T now add some 

 further comments thereto. 



In the present specimens, the amorphous or soluble silica 

 of which their spicular skeletons were originally composed, 

 has entirely disappeared, and the spicules now consist of 

 iron pyrites. This replacement by pyrites is of common 

 occurrence, more particularly in a matrix o*" black shales; 

 for example, the earliest known sponge, Protospongia fenes- 

 trata, Salter, from the Cambrian rocks of South Wales, is in 

 the same mineral condition, and in a nearly similar matrix, 

 as the specimens from the Quebec group and the Utica 

 shale. When thus replaced, the general outline of the 

 larger spicules is fairly distinct, but wh-^re the spicules 

 are minute, and in close proximity to each other, their in- 

 dividual outlines are blurred by the tendency of the crystals 

 of the rep' 'ing pyrites to amalgamate together so as to 

 form a coutiuuous film of the mineral in which the finer 

 spicular structures are quite indistinguishable. This coales- 

 cence of the pyrites likewise makes it very difficult to de- 

 termine whether the spicular elements of the sponge were 

 organically soldered together into a silicious mesh, or 

 whether they were merely held in their natui'al positions 

 by the soit animal structures, and owe their present union 

 to subsequent fossilization. 



Next to the chemical changes, we have to take into 



