that afford the Stonesfield- slate. i^l5 



The total depth of this shaft, to the bottom of the drift, or 

 horizontal gallery where the slate is dug, was about sixty-eight 

 feet; the drift itself being between five and six feet in height. 

 About twenty-five feet of the lower beds (7.) consisted of fine- 

 grained oolitic lime-stone, containing casts of spiral univalves and 

 bivalves* ; and the remainder, or upper part. (1. to 6.) of alterna- 

 tions of clay, with limestone, probably belonging to the corn- 

 brash, — the beds of which at top are rubbly, and lower down 

 oolitic. The lowest of these clay beds (6.) is of a greenish hue ; 

 it effervesces slightly with acids, and falls to pieces in water like 

 fullers' earth : and the upper bed of clay (2.) contains numerous 

 plicated terebratulites, with pectens, and other marine fossils.t 



The stone which affords the " slate," occurs in irregular masses 

 within a bed of sand (8.), and is analogous to those concretions 

 of calcareous grit, or of sand agglutinated by carbonate of lime, 

 that form a part of almost every group, from the beds above the 

 chalk, down to the bottom of the lower oolite; — and of which the 

 quarries on the east of Cowes in the Isle of Wight, certain va- 

 rieties of the Kentish rag, the grit of Hastings, and of Tilgate 

 forest, the remarkable nodules of the coast near Boulogne, and 

 the gritty limestone beneath the inferior oolite, may be cited as cx» 

 amples. In fact, wherever sand contains a large proportion of 

 calcareous matter, concretions of this kind are to be expected ; 

 and the presence of oolitic particles in this case is almost the only 

 mineralogical distinction. 



The subjoined sketch represents a section of the drift from 

 whence the stone is extracted; the names in Italics being those 



* Of the genera Turritella ? Venus, Astarte ? Tellina, Pecten (vagans ?) 



+ Terebratula obsoleta. Min. Conch. Tab. 83. fig. 7. Pecten fibrosus. 

 Tab. 136. fiff. 2. 



