ON THE FIGURE OK SULPHATE OF BARYTES, &C. 253 



VIII. 



On the Figure of Sulphate of Barj/tcs, and the Formation pf 

 Mandreporte. In a Letter from Mr. H.Sarjeant^ 



To Mr. NICHOLSON. 

 SIR, 



I F the following mineralogical notices appear to contain any 

 thing worthy of attention, they are at your fervice, from 



Your humble fervant, 

 Kefwich,July 16*, 1802. H. SARjEANT. 



THE barytes, or ponderous earth, occurs in a great variety 

 of forms : one of the rareft is defcribed as " refembling a nnm- 

 <f, ber of fmall double convex lenfes fet edgeways in a ground." 

 This Angular formation, fo different from the angular forms 

 afFecled by cryftals in general, was the caufe of my examining 

 it with confiderable attention ; and I am perfuaded, that who- 

 ever does the fame, will perceive that the fhape of thefe cryf- 

 tals is not, properly fpeaking, lenticular, but rather a fort of 

 very acute edged rhomboid, inferted by one of the corners as 

 far as the diagonal line, fo that the projecting part referable* 

 the corner of a carpenter's chiffel, admitting that the angle . 

 formed by its edge and tide were enlarged to ] 00 degrees, or 

 fomewhat more, and the fide bevilled off in the fame manner 

 as the edge, but in the oppolite direction. 



In its moft ufual form, the fulphate, the barytes is a very- 

 abundant production. It is found in this and the neighbour- 

 ing counties, in great quantities, with lead, with lime (common 

 limeftone), with iron, and with gypfum. 



That fort of limeftone which abounds with the petrefa&ions 

 called mandreporce, appears to owe its origin to depofitions of 

 calcareous mud, formed in a manner fimilar to what may be 

 feen in the upper part of moft lakes, that of Kefwick in parti- 

 cular, in which a fpecies of equifetum grows, often in meets of 

 feveral acres, flightly covered with water. The fe&ion of the 

 madreporce is precifely that of the frefh root, and they are ge-s 

 nerally inclined all in the fame direction, as if caufed by a 

 ftream of water paffing over them, which might be the cafe 

 when the water was drawn off from fuch places, by the effect 

 of earthquakes, or other great operations of nature. 



The fubfequent induration of fuch mud into ftone, may be 

 contidered as a fact fufficiently known, 



IX. Experiments 



