232 NEW RED SANDSTONE. 



this striation he believed to be due to local friction, subsequent 

 to the deposition of the beds.' (See p. 217.) 



At East Harptree beds of chert are associated with the marls and 

 conglomerates.- 



In the Dolomitic Conglomerate of Durdham Down, near Bristol, 

 some Dinosaurian remains were found in 1836; these belong to 

 the genera Palceosaurus and Thecodontosaurus, and were originally- 

 described by Dr. H. Riley and Mr. S. Stutchbury.^ (See Fig. 26, 

 p. 172.) Three-toed footprints of Brontozoum have more recently 

 been discovered in similar rock at Newton Nottage, in Gla- 

 morganshire.* 



The remarkably even manner in which the Carboniferous Lime- 

 stone has been denuded is well shown at Wallcombe, near Wells, 

 where the Keuper beds rest on the edges of that rock. This 

 even line is also very conspicuous in the vales near Frome, beneath 

 the Rhaetic Beds, Lias, and Oolites. The Conglomerate sometimes 

 makes fine bold scenery, presenting mural faces, as at Croscombe 

 near Shepton Mallet, Wookey Hole, and Haydon Gully near East 

 Harptree. 



The road to Wookey Hall on one side of Wells, and that leading to Dulcot on 

 the other, show in places in the Red Marl a bed termed the ' Wonder Stone,' 

 described by Buckland and Conybeare as * a beautiful breccia, consisting of yellow- 

 transparent crystals of carbonate of lime, disseminated through a dark red earthy 

 dolomite.' 



Beds of Dolomitic or Magnesian Limestone are conspicuous near Clevedon, and 

 on the Glamorganshire coast, south of Penarth. At the former place the rock is 

 fine-grained, and has been sculptured into architectural ornaments. 



The Dolomitic Conglomerate is sometimes burnt for lime ; it is also employed 

 for building, and polished for ornamental purposes. The Draycot Stone, 

 quarried near Axbridge, is well known in the district. 



Red and brown oxides of iron are not uncommon in the Dolomitic Conglo- 

 merate, and they have been worked in many places, as at Llantrissant and Llan- 

 harry in Glamorganshire,^ on the Mendip Hills, etc. Reddle (or raddle) has been 

 largely dug at Winford near Chew Magna, for the manufacture of pigments. Ores 

 of lead and zinc occur in the Mendip Hills. 



At various localities large brown siliceous nodules are found in the Dolomitic 

 Conglomerate ; these are hollow and lined with crystals of quartz, of which the 

 purest forms are known as Rock-crystal, and locally as 'Bristol diamonds.' The 

 nodules or geodes are termed 'Potatoe Stones,' and they vary from an inch to a foot 

 in diameter. They occur at Westbury near Bristol, Clevedon, Banwell, Sandford, 

 Chilcompton, and other places. They sometimes contain crystals of Celestine, and 

 Calc-spar. The formation of these geodes is a problem. The crystals of quartz 

 which line the drusy cavities must have been deposited from solution, and probably 

 by very slow evaporation, from the infiltration of water holding siliceous matter. 

 According to Prof. T. Rupert Jones, their origin is pseudomorphic, silica having 

 replaced the outer portions of limestone fragments.^ 



Calcareous Sandstones, worked for building-purposes, are met with at Claver- 

 ham Court, near Yatton (Claverham orClarham Stone), Brislington, Chew Magna, 

 Sutton Mallet, near Chew Stoke, Litton, Pyle in Glamorganshire, etc. The upper 



1 G. Mag. 1 88 1, p. 72 ; E. D. Jones, P. Geol. Assoc, vii. 346. 



- Geology East Somerset, etc. (Geol. Survey), p. 60 ; G. Mag. 1 871, p. 400. 



3 T. G. S. (2), V. 349 ; T. H. Huxley, Q.J. xxvi. 43. 



* W. J. Sollas and J. Storrie, Q.J. xxxv. 515. 



^ Watson. Geologist, ii. 241. 



^ Proc. Geol. Assoc, iv. 454 ; see also Buckland, Trans. G. S. (2), iii. 421. 



