202 



THE GEOLOGIST. 



Syerford Com- 

 mon. . . . 



We shall now proceed with a description of the beds in 

 the ascending order, upon the same plan as that which was 

 adopted in describing the beds of the lias formation. 



The first bed, then, which occurs, is the pisolite, or pea- 

 grit, composed of small concretionary masses, of a light 

 ochreous colour, having a kind of nucleus within, of a 

 somewhat darker tint, and more or less flattened, and many 

 of them are so covered with a very minute coralline as to 

 give them the appearance of organised structure ; their chief 

 chemical constituent is carbonate of lime, the colour being 

 derived from peroxide of iron ; these masses are plentifully 

 mixed with fragments of small shells, portions of penta- 

 crinites, portions of several small species of cidaris, and mi- 

 nute corallines of several species; these are all firmly cemented 

 together, and present in the aggregate a rock varying in 

 thickness from eight to ten feet ; it is quarried for gate-posts. 



