VOL. XXXV.] PHILOSOPHICAL TRANSACTIONS. 253 



Of the several Strata of Earths and Fossils, found in sinking the Mineral IVells 

 at Holt, in JViltshire. By the Rev. Mr. Lewis, Ficar of the Place. Com- 

 municated by John Brome, Esq. N° 403, p. 489. 



After having passed the upper turf, they came to a blue clay, which held 

 about 3 feet; then they met with a yellow, brittle clay, much resembling ochre, 

 used by painters, about 2 feet in thickness; and next with a loam of a looser 

 texture, which sparkled with a kind of talc, called by the naturalists selenites, 

 and was intermixed with yellow ochre. These selenites, which were plentifully 

 found shot in the clay, were crystals consisting of transparent, shining, brittle 

 flakes, some of a rhomboidal, others of a conical figure, but all hexaedra, or 

 columns of 6 sides. They had no sensible taste of salt, and the clay in which 

 they were found was interspersed with veins of coloured earth, of the colour 

 of sulphur and iron rust. 



Below this, at about 10 feet deep, they came to a bed of stones, of a large 

 size and very hard texture, coated with flakes of gypsum of a white and yel- 

 lowish colour, which ran through and divided them, as it were by various mem- 

 branes, into different cells, all filled with hardened loam of a grey colour. 

 These stones, which were all of an oval figure, in shape resembling pebbles, 

 weighed from JO to 60 lb. weight, and lay all on a level, one by another in the 

 bed of clay. Here the springs come in, and below this the clay was darker 

 coloured, and interlaid with small shells of the oyster, escallop, and muscle 

 kind, and with a few belemnites curiously shaped. Here they met with stones 

 of a very close texture, which when washed seemed to be nothing but a mass 

 of shells jumbled and embodied together. And a little lower the clay produced 

 some lumps of a black, bituminous sulphur, interlaid with some small thin 

 laminae, seeming to be metalline, and bright, like the purest silver; on firing 

 this sulphureous bitumen on a red-hot iron, it emitted a blue flame, and strong 

 smell, like brimstone, but the metal was lost. 



From this account of the different strata found in sinking these wells, their 

 impregnation seems to be from alum, vitriol of steel, ochre and sulphur, and 

 from an accurate mixture of all these, which no art can imitate, it seems to 

 derive those admirable qualities with which it is endued. Some conjecture may 

 be made of its nature and qualities, from the tinctures it gives on chemical 

 experiments; with astringent drugs, as galls, oak-leaves, and balaustians, it 

 sometimes tinges red, inclining to purple, and sometimes will not tinge at all ; 

 with volatile alkalies, as spirit of urine, and sal ammoniac, it turns milky; with 



