Geological Society. 137 



the new-red-sandstone formation which surrounds the Mendip Hills. 

 Their prevailing colours are various shades of gray ; their internal 

 structure resembles that of the bird's-eye agate, presenting alternate 

 bands of chalcedony, jasper, and hornstone, disposed in irregular and 

 concentric curves : some specimens from Worle and Clevedon are of 

 the nature of fine jasper-agates, and of a bright red colour. 



A shallow pit, from which the agates are extracted at Sandford, 

 piesents the following section. 



1. Yellow clay, mixed with magnesia and carbonate of 1 g inches. 



lime ; J 



2. Yellow dolomite, used as firestone in limekilns j it T 



crumbles readily to a soft powder, and is filled with I g inches. 



specks of manganese, and contains veins of small [ 



nodules of chalcedony J 



.3. Yellow clay falling to powder in water like Fuller's '\ 



earth, and containing much carbonate of lime and V, g inches. 



magnesia. In this clay the agates are dispersed { 



irregularly like nodules of flint in chalk J 



4. Yellow clay and earthy dolomite, to the bottom of 1 jg inches. 



the pit J 



The author adduces a parallel example of beds and nodules of jas- 

 per and jasper-agate in the mountains of dolomite, near Palermo, 

 in a formation of the same age with the new-red-sandstone of the 

 Mendip Hills. He also gives examples of agates formed in cavities 

 of chert of the green-sand formation, near Lyme Regis, and in 

 cavities of silicified wood and silicified corals and shells. The most 

 beautiful specimens of the two former are from the tertiary strata of 

 Antigua. Shells converted into chalcedony, and containing agates in 

 their cavities, occur near Exeter, in the whet stone-pits of the green- 

 sand formation, at Black Down Hill ; and shells, entirely converted to 

 red jasper, in sand of the same formation, occur at Little Haldon Hill. 

 A paper was next read " On the tertiary fresh- water formations of Aix 

 in Provence, including the coal-field of Fuveau," by Roderick Impey 

 Murchison, Esq., Sec. G.S., F.R.S., &c., and Charles Lyell, Esq., 

 For. Sec. G.S., F.R.S., &c.; with a description of fossil insects con- 

 tained therein, by John Curtis, Esq., F.L.S. 



The oldest and fundamental rock of this district is a highly in- 

 clined and contorted secondary limestone, containing Belemnites, 

 Gryphites and Terebratulae ; on which is unconformably deposited a 

 vast fresh-water formation, the relations of which are shown in a 

 section from N.E. to S.W.— The escarpment of white marl and linie- 

 stonc, N.E. of the town of Aix, is first described in a descending 

 series. The upper beds, consisting of white calcareous marls and 

 marlstone, calcareo-siliceous millstone and resinous flint, contain 

 the Potamides Lamarckii, Bulinus terebra and B. jiygmaeus, with a 

 new species of Cyclas named C. gibbosa ; and the subjacent strata 

 run out into a terrace, beneath which gypsum is extensively worked. 

 Of these beds (minutely detailed), some are peculiarly character- 

 ized by their abundance of fossil fish ; and others by a profusion 

 of plants, amongst which, Mr. Lindlcy has recognised Flabellaria 

 N.S. Vol. G. No. 32. Aug. 1829. T Lf»ma- 



