136 TKOCEEDINGS OE THE GEOLOGICAL SOCIETY. [Jan. 8, 



in the Trias on the flanks of the Mendips *. All observers, how- 

 ever, agree that the rock is of a remarkably peculiar and almost 

 unique character, Mr. Symonds calling it " a most distinguishable 

 rock." To obviate confusion, I use a term which does not involve 

 any theoretical views, and which was first applied to it by Dr. 

 Gordon of Birnie f , who has done so much for the elucidation of the 

 geology of this difficult district, both by his own observations and 

 by constantly placing his great local knowledge at the service of 

 other investigators. 



The mass of the Stotfield rock is composed principally of calca- 

 reous and siliceous materials. The former is usually a hard, com- 

 pact, impure limestone, of a cream-colour, which in places becomes 

 crystallized and exhibits fine examples of calc- spar, with fibrous and 

 radiated carbonate of lime. The latter forms nodules and caver- 

 nous masses imbedded in the former, and consists of compact cherty 

 or flinty material, occasionally exhibiting the banded structure of 

 jaspers and agates, and containing drusy cavities incrusted with 

 crystals of quartz or mammillated coatings of chalcedony. With 

 these principal materials there is often associated an amorphous ar- 

 gillaceous mineral, of a greenish colour ; while beautifully crystal- 

 lized galena, pyrites, and blende are sometimes disseminated through 

 the mass as accidental ingredients. 



The total thickness of this rock is unknown, its upper portion 

 being always denuded away ; but it is said to have been dug to the 

 depth of 30 feet J. When exposed to weathering action, the cal- 

 careous portion of the rock is removed, and the hard indestructible 

 masses of cherty material remain. Where the rock is covered with 

 Boulder-clay, pits were formerly dug into it ; and the most purely 

 calcareous masses being selected, they were burned into lime ; but 

 the tendency of the material, when the siliceous portions were not 

 rigidly excluded, to fuse into solid masses in the kiln, and the su- 

 periority of the Silurian limestones of Banffshire, have led to the 

 almost total abandonment of these old pits. Several attempts have 

 been made at Stotfield to work the galena, which is associated with 

 this rock there, as also at Inverugie and other points ; but, owing to 

 the fact of the metallic ores being disseminated through the mass 

 and not collected into veins, these attempts have proved futile. 



The origin of this peculiar rock, which is altogether destitute of 

 any trace of organic remains, is a very interesting problem. 

 That its formation must be referred to purely chemical agencies is, 

 I think, in the highest degree probable ; but into this question I do 

 not propose to enter, it beiug sufficient for my present purpose to 

 point out the highly peculiar, if not unique, character of the rock, 

 and the consequent facility with which it can be identified. 



B. " The Reptiliferous Sandstone." — This lower division of the 

 formation consists of beds of sandstone, sometimes slightly calcareous, 

 and usually of a pale colour inclining to yellow ; it has often grains 



* Quart. Journ. Geol. Soc. toI. xvi. (1860) p. 446. 

 t "Edin. New Phil. Journ. New Ser. vol. is. (1859) p. 15. 

 X Duff, < Sketch of the Geology of Moray ' (1842), p. 23. 



