Mr. Lonsdale on the Oolitic District of Bath. 2Q3 



perishable limestone, which has scarcely a trace of oolitic texture. The beds 

 are divided into blocks by seams oblique to the plane of stratification. The 

 colour of the stone is pale yellow, except where it is in contact with the sub- 

 jacent clay, when it is blue. 



The rubbly oolite (2 h) constitutes the greater part of the coral rag of Wilt- 

 shire. It is formed of a nodular limestone of an earthy aspect, a brownish, yel- 

 lowish, or blueish- white colour, and abounds with fragments of Echini and 

 shells. Sometimes the nodules possess sufficient hardness to be used in the 

 repair of the roads, but they are much oftener soft and unserviceable. The 

 oviform particles are frequently very indistinct, or extremely small ; but in that 

 variety which is called pisolite, they are numerous, and are sometimes three 

 tenths of an inch in diameter. In the neighbourhood of Spirthill the stone 

 acquires a beautifully oolitic character, the spherules being regularly formed. 

 Thin beds of clay occur in many of the quarries, and give them the appear- 

 ance of a regular stratification ; but these divisions are not to be traced for 

 any distance. 



The irregular beds of Polyparia (2 c) consist of nodules or masses of cry- 

 stallized carbonate of lime, which afford invariably evidences of the labours 

 of the Polypus ; and associated with them are others of earthy limestone, 

 which bear only partial proofs of an organic origin. The whole are con- 

 nected by a pale blueish or yellowish, stiff clay. It happens frequently that 

 a bed is composed of one genus of Polyparia. At Calne and Westhook the 

 prevailing fossil is a small species of Astrea; at Hannington Hill near High- 

 worth, Caryophyllia form the entire mass of the coral rag : but at Steeple 

 Ashton both these genera are associated with Agaricia. 



The bottom bed of the coral rag occasionally affords a dark blue, crystalline 

 rock, which bears considerable resemblance to some varieties of the carboni- 

 ferous limestone. Quartz crystals and flint sometimes occur in this division. 



3. The clay which separates the strata we have been considering from the 

 lower calcareous grit has a pale blue colour, is of a stiff nature, and effervesces 

 slightly with acids. It is apparently co-extensive with the formation from 

 Lynham to Westbury Field. 



4. The fourth division of the coral rag, the lower calcareous grit, consists 

 of a thick stratum of sand, inclosing irregular beds of a siliceous rock. The 

 sand is more or less intermixed with calcareous matter, arising principally 

 from the decay of organic remains. The particles are generally small, and 

 are never intermingled with rounded pebbles. The prevailing colour is dingy 

 yellow, of various shades. Thin laminae of clay are not unfrequently dispersed 

 through the sand. 



