XIX. — On the occun^ence of Agates in Dolomitic Strata of the New 

 Red Sandstone Fonnation m the Mendip Hills. 



By the Rev. WILLIAM BUCKLAND, D.D., P.G.S. F.R.S. F.L.S. 



(professor of geology and mineralogy in the university of oxford.) 



[Read June 19, 1829.] 



JjlAVING had occasion to visit the cliOfs of Cheddar in November 1827, I 

 found in the collections of g-eodes and calcareous spar which are there exposed 

 to sale, a number of curiously figured agates, such as I had never before seen 

 during my numerous geological investigations of the Mendip Hills, nor in any 

 of the cabinets at Bristol which abound in the products of this district. I was 

 informed that they were ploughed out of the surface of some fields at the base 

 of the Mendips, and collected from holes dug for this purpose to a slight 

 depth where the plough indicated their abundance. I had then no leisure to 

 examine the spot whence they came, but wrote to a geological friend (the 

 Rev. D. Williams of Bleadon, to whom we owe the discovery of vestiges of 

 another hyena's den at Uphill), requesting him to ascertain the exact place 

 whence these agates were taken, and on being informed that it was in the 

 village of Sandford, about two miles east of Banwell, I visited the spot with 

 him in November 1828, and found their matrix to be the dolomitic strata of 

 the new red sandstone formation. 



As they are the first examples I have ever met with, of the occurrence of 

 perfect agates in this formation, 1 send specimens to the Geological Society, 

 in illustration of the present communication. 



In external form and size, these agates resemble the ordinary varieties of a 

 common potatoe ; they are, in fact, very nearly allied to those geodes, to 

 which the name of potatoe-stones has been generally applied, and which have 

 been long known to abound in the dolomitic beds of the new red sandstone 

 formation around the Mendip Hills. Their exterior is rugged, like that of a 

 truffle, and opaque ; but on being broken they present internally, on a larger 

 scale, the same structure and arrangement as the compound agates known in 

 jewelry by the name of bird's-eye agates, being made up of alternating bands 

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



VOL. III. SECOND series. 3 I 



