O F S T O N E S. 79 



and found them fingle, in a linear pofition. The floods often 

 turn them out of their argillaceous nidus's, and fmooth their fur- 

 faces, when their tranfverfe and longitudinal Jlrie are feen to 

 great perfection. 



Their moft ufual fhape is conoid, but we fometimes find them 

 of an irregular ihape, and fcyphiform, or cuped, like the cup- 

 mufhroom, with fine^n> in alternate ridges and furrows, from 

 a protuberated center in the cup to the circumference, and alfo 

 length-ways. I have one of thefe of an inch and a half in dia- 

 meter, an inch and three quarters long, and four inches round ; 

 found in the bottom of the fame brook, with a fmall conoid cuped 

 mycetetes, with the fame kind ofjtri<e in the cup, and other larger 

 round it. 



We have them alfo in ftone on the fame fhore of a 

 fliape, with an obtufe reflected apex underneath, of various co- 

 lours ; of a light and deep afh-colour ; of a pearl-colour, with 

 a beautiful blufli of red ; of a deep purple and white. They 

 take an excellent polim. It is not uncommon to find this and 

 the conoid fpecies entombed in large loofe maJTes of a greyifli- 

 black hard ftone, in company with the grey and white undulated 

 lithojlrotion, entrochoi, and bivalve mells, great and fmall, in a 

 moft amazing confufion. 



All the coralloid clafs are of a marine origin, the marmoreous 

 cafts of fea-coralloids, compofed of longitudinal and tranfverfe 

 /amellte, fo thin, as to form the beautiful radiated figures de- 

 fcribed. Sections of them cut through both ways give a good 

 view of their interior ftructure. They calcine to a white lime. 



Of the figured ftones, called Belemnitt, or thunderbolts, the 

 Trochitx, Entrochoi, AJleria, or ftar-ftones, compofed of talc and 



fpar, 



