On the Microscopical Structure of the Calcareous Grit of the Yorkshire Coast

Abstract

The calcareous grit is a sandstone containing a variable quantity of carbonate of lime, which lies just below the coralline oolite. Good sections of it may he seen at Filey, Gristhorpe Bay, and Scarborough. A great part of it is only a sandstone containing a variable quantity of calcareous matter, hut a considerable portion contains a great deal, and is much hardened by the infiltration of agate, which has silicified many of the shells and the wood, and filled the chambers of many of the ammonites. It is to this part of the bed that I wish to call attention. If a piece of it be dissolved in hydrochloric acid, we obtain portions of agatized shells, and a quantity of sandy matter, which, without further examination, would naturally be thought to be merely sand, and such it has hitherto been considered. When, however, examined with a microscope, it is at once seen to contain a very large quantity of reniform bodies, which are evidently not sand, but some kind of minute organisms converted into agate. The mere occurrence of minute agatized shells in this deposit would certainly not be a fact worthy of being laid before this Society, but since they exist in such vast numbers as to constitute a very considerable portion of a well-known rock, and, by the manner in which they occur, are presented to us in a form that is additionally interesting, perhaps a detailed account of them will not be thought a subject unworthy of ...