260 ON A NEW LYSSAKENE HEXACTINELLID EEOlt CANADA. 



explained the origin and formation of the spicnlar strata which 

 he had described on this and other occasions. He thought that 

 Dr. Wallich's hypothesis of the conversion of extensive layers of 

 sponge-protoplasm into black flint elucidated many, but not all, of 

 the phenomena connected with the origin of such siliceons strata as 

 flint and chert. He stated that sponge-spicules, and nnmerons 

 other Microzoa from the Upper Silurian shales of Shropshire, had 

 been noticed lately by Mr. Smith of Kilwinning. 



Dr. Hicks said that it was remarkable that chert was not asso- 

 ciated with Protospongia, as, on either Dr. AVallich's or Prof. Sollas's 

 view, might have been expected. 



Prof. Jttdd said that, as the solution of siliceous organisms had 

 been recently doubted. Prof. Sollas's observations were of additional 

 interest. He himself fully believed that this solution did take 

 place ; now and then he had found, in examining the residues left 

 by dissolving chalk in acid, the thickest portions of siliceous spicules 

 still remaining not quite destroyed in chalk. 



Prof. Sollas replied that he believed a spicule had been described 

 by Mr. Carter similar to that mentioned by Prof. Duncan. The one 

 described now by him, however, was much more robust. He had 

 never been able to find spicules in the Wenlock. He could not 

 comprehend what Dr. Wallich's views really were. That none of 

 the fossil siliceous spicules which the author had described were 

 originally calcareous was quite certain. As for Protospongia, it 

 did not occur in limestone, and bore a very small proportion to the 

 mass of the bed ; and this might account for the absence of the 

 chert. 



