72 Transactions of the 



of hills, and together with the quarries, leave many sections of the 

 rocks which afford excellent opportunities for examining them. 

 The Bath or compound great oolite, is found at the top of most 

 of these hills, and near Minchinhampton, broken up by the great 

 Brinscomb and Woodchester valleys. At the bottom of these 

 valleys is a layer of clay, covered by a thin layer of sand, above 

 which comes the inferior oolite, then the fuller's-earth, and at the 

 top the great oolite, in the exact order of deposition. The inferior 

 oolite is chiefly ragstone, while the upper beds are called weather- 

 stone. These attain a thickness of 130 feet, the mineral character 

 of the beds presenting the greatest variety, it. being not unusual 

 to find rich, shelly limestone passing into sandstone in tl^e same 

 quarry. The great oolite proper may be conveniently divided into 

 three parts, the upper and lower of which are fossiliferous, the 

 middle barren. Several of the upper beds are hard, and the 

 fossils are seldom obtained entire, while the stone of the lower 

 part admits being divided with a knife. This lower subdivision 

 is 35 or 40 feet thick. The uppermost portion of this series, 

 called planking — the local name denoting any thin-bedded stone 

 — is 8 or 10 feet in thickness, and contains many fossils, several 

 of them being trachelipods, of whicli I shall have to speak after- 

 wards. Under this comes an incoherent sandstone, almost desti- 

 tute of shells. Gradually the shells become more numerous, and 

 rest on several beds of the hard shelly rock called weatherstone. 

 A little lower down, the structure of the organic remains impart 

 such a hardness to the rock that fire is struck by workmen's tools. 

 These shelly beds are extremely durable, but of coarse aspect ; 

 when once dried by exposure to the sun, they do not readily absorb 

 water, and consequently resist frost. 



Beneath these beds we find the fuller's-earth, which is only im- 

 perfectly developed within the district. It consists of a series of 

 blue and brown marls, and clays traversed by three or four bands 

 of liard argillaceous rock, locally known as clay-rag. Some por- 

 tions of these clays, and more especially the ragstones, are made 

 up of the valves of the Ostrea acuminata, the only fossil of the 

 series which is not peculiar to any bed. The numerical propor- 

 tion of geneually known species that are obtained from the great 

 oolite are — Bivalves, 160 ; univalves, 140 ; radiaria, 13 or 14 ; 

 cephalopoda, about 10. Of the latter, 6 are ammonites, which are, 

 however, extremely scarce — in fact, the cephalopoda are seldom 

 found in the' beds between the inferior oolite, in which they 

 abounded, and the Oxford clay and Portland oolite. 



In the middle of the inferior oolite, a band of freestone is found 

 which is used for building, surrounded on both sides by ragstone. 

 Several fossils are found here also. The sand which succeeds 



