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

Abstract

If a piece of that part of the calcareous grit just below the coralline oolite, which contains numerous agatized shells, 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 subiect unworthy of attention. The chemical composition of a specimen containing no large shells was determined by dissolving it in hydrochloric acid; and the fine muddy matter was separated from the coarser sandy portion by suspension in water and decantation; from which I found that we had in 100 parts— This coarse matter consisted, in nearly equal proportions, of the reniform agatized bodies, and sand, whose particles varied in size from 1/100th to 1/2000th of an inch, the average being 1/200th, of which the great bulk was composed.