Mr. Lonsdale on the Oolitic District of Bath. 251 



it presents an uniform texture and softness, yields easily to the saw, and is 

 admirably adapted for the chisel of the sculptor. In those beds in which 

 fragments of shells abound, the formation acquires the texture of forest 

 marble ; and towards the top of the series, where Polyparia exist, the rock 

 assumes the appearance of some varieties of the coral rag-. 



The whole of the strata composing the g-reat oolite may be arranged 

 under the followin"- heads. 



1. Upper rags* . . 



2. Fine freestones 



3. Lower rags . . . 



Subordinate divisions. Thickness. 



Coarse, shelly limestones ~| 



Tolerably fine oolites \ 20 to 53 feet. 



Tough, brown, argillaceous limestone J 



10 to 30 feet. 



Coarse, shelly limestones 10 to 40 feet. 



1. The subordinate divisions composing the upper rags alternate together 

 several times. The coarse shelly limestones (1. a.), the beds to which the term 

 rag is generally confined, possess, for the greater part, an imperfectly oolitic 

 structure ; and the oviform spherules are sometimes entirely wanting. The 

 stone yields with difficulty to the saw, and the stratum immediately below the 

 Bradford clay is extremely tough, and loses almost all the characters of an 

 oolite. Some of the beds consist principally of Polyparia, and were identified 

 by Messrs. De Basterot and Desnoyers with the calcaire a Pob/picrs of 

 Lamouroux at Caen in Normandy. The colour of the stone is chiefly yel- 

 lowish white, but at the junction of the Bradford clay it is blue. The tole- 

 rably fine oolites (1. b) sometimes possess a beautifully distinct texture, the 

 spherules being perfectly defined. These beds are easily worked, but appear 

 to be of a more perishable nature than the fine freestones (2.). The tough, 

 brown, argillaceous limestone (1. c) is of a close, compact structure; it in- 

 closes organic remains, and after long exposure to the weather often acquires 

 a cavernous appearance, similar to that which is called rustic work by archi- 

 tects. A bed of clay occurs about the centre of the upper rags. It is of a 

 pale blue colour, and contains a few slabs of a brownish limestone. 



2. The fine freestones vary in the number and thickness of their beds. 

 They are principally distinguished from each other by the greater or less 

 decisiveness of the oviform particles, which are occasionally so very obscure 

 that the rock becomes earthy and indistinct in its texture. 



3. The lower rags consist partly of shelly limestones, in which the organic 

 remains are sometimes so numerous as to compose almost the entire mass, and 

 partly of coarse freestone, used occasionally for rough walls, and formerly to a 

 considerable extent in building. The bottom bed, which rests immediately 



* The word " rag" is applied by the quarrymen to those beds of the great oolite which contain 

 many fragments of shells, and are not easy to work. 



2k2 



