78 Mr Grimes 1 Observations on the Flints in Warwickshire. 



We have three kinds of chalk-flints in this country, which, 

 like those of all others, I helieve, have some central part more 

 opaque than the rest, as though there had been a nucleus of 

 matter, (perhaps organic,) but without any distinct outline. 

 Parts of shells are often enveloped in them, which occasional- 

 ly retain their calcareous character, sometimes with a fibrous, 

 sometimes with a spathose structure. They are all porous or 

 vesicular, but in different decrees. 



The most compact is the black flint, which is also the most 

 brittle, and the easiest of fracture. Those which appear to be 

 the most porous (if porous they be,) are the translucent grey 

 flints ; and the most cohesive are of a muddy-yellowish, red- 

 dish-grey, slightly, if at all translucent, and these, perhaps, 

 are the most vesicular, owing to their containing more remains 

 of shells, &c. 



They all contain either water, or some other fluid, possibly 

 more volatile. On breaking the stone, it may be seen exuding 

 from the vesicles, by applying the eye quickly in a strong re- 

 flected light. 



I have found that sometimes a slight film is deposited by 

 this fluid, resembling the effect of gum-water. It is not af- 

 fected by acids, but easily removed by the finger, and even by 

 the action of water poured upon it. 



More frequently, however, are to be found upon the flaws 

 of the stone little stellular concretions, (see specimen letter B,) 

 evidently produced in the same way. These, when the exu- 

 dation has been sufficient, take a more decided character, be- 

 coming minute fibrous crystals, either cuneiform or diverging 

 and rose-like. (Specimen, letter C.) 



This same substance is still more frequently to be found in 

 much larger quantities, circularly arranged round a centre, 

 which has the appearance of being a small orifice. It is of- 

 ten, at the outer edge, of the size and thickness of a wafer, 

 (see specimen, letter D :) these three latter adhere firmly to 

 the stone. The flakes generally split when the stone is sepa- 

 rated by a blow, one half adhering to each side ; and one may 

 often perceive the same ragged stringy appearance, so often 

 exhibited, and more particularly visible in the common frac- 

 ture of a black flint. 



