On a new Genus of Siliceous Sponges from the Lower Calcareous Grit of Yorkshire

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Abstract
Nearly forty years since, Dr. H. C. Sorby, F.R.S., communicated to this Society a paper on the microscopical structure of the Calcareous Grit of the Yorkshire coast, in which reference was made more particularly to the nature of certain microscopic reniform bodies with which the rock ill places was largely filled. In mineral constitution some of these bodies were of calcite, others of chalcedonic silica, whilst ill others both these minerals were present, and the question as to their original constitution was decided by Dr. Sorby in favour of the calcite, since it was thought extremely iml;robable that, if originally of silica, this material would have been dissolved and replaced by calcite, whereas the substitution of silica in place of calcite was a well-known phenomenon. The definite tbrm and outline of these bodies left no doubt that they were of organic origin, and Dr. Sorby recognized their resemblance to the small siliceous globules which form an outer crust to many existing sponges, but rejected this view on the ground of their supposed calcareous nature, trod he finally concluded that they were small shells, possibly Foraminiferal, in whose inteiior calcareous or siliceous materials had been infiltrated, in the same manner as in the chambers of the Ammonites occurring in the same rock. Subsequently, in 1876, Prof. J. F. Blake, F.G.S., discovered similar minute bodies in rocks of nearly the same age in Dorsetshire and Wiltshire, and noticed that some of them were hollows enclosed by thin crusts or shells, which dissolved

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