492 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



situated to the north-west of the highest Carboniferous-limestone 

 platform of the Mendips. A mile to the north, the Old Red Sand- 

 stone, surrounded by the Carboniferous -limestone shales, is present, 

 the Carboniferous Limestone itself, both on its north and south 

 flanks, being fringed by Dolomitic Conglomerate, beyond which the 

 New Red Sandstone succeeds. 



The nearest horizontal deposit of Liassic age to the north is at 

 Nempnett, 2| miles distant, which yields Pecten Pollux and Lima 

 tuherculata. Two miles to the east, above Harptree, a Carboniferous- 

 limestone basin is filled with a siliceousLiassic deposit, in which are 

 an abundance of Lima gigantea and Pecten Pollux, whilst to the south- 

 west this formation is six miles removed. 



In examining some blocks of conglomerate brought out of the 

 above workings, I detected part of a Cidaris Eclwardsii, and was 

 thus induced to give a closer attention to it than I otherwise in- 

 tended. The shaft was then covered up ; but near it was a small 

 heap of blue clay in which I found Rhynchonella variabilis and 

 fragments of other shells, evidently of Liassic age. I was in- 

 formed by one of the miners that this clay had been brought from 

 the lowest part of the mine, before it had ceased working. To prove 

 the correctness of this statement, and learning that the ladders had 

 been left in, I induced the manager of the adjoining works to un- 

 cover the shaft that I might go down for its examination, — a work, 

 from the state of the shaft, not unattended with some danger. On 

 descending I examined several of the upper galleries, and found 

 the materials therein chiefly composed of crystalline carbonate of 

 lime, giving place occasionally to sulphate of barytes, conglomerate, 

 and thin bands of vertical limestone, with all the ordinary features of 

 a mineral vein. Prom the end of one of the galleries, at a depth of 

 about 90 feet, I secured some samples of what appeared to be a 

 sandy deposit, but which, when washed, was found to be almost 

 entirely composed of the dismembered joints of Encrinites, chiefly (if 

 not wholly) of Carboniferous-limestone age, and with occasional 

 small pebbles of hgematite iron-ore. 



Proceeding to the bottom of the shaft, at a depth of 270 feet, I 

 had the pleasure of reaching the object of my search, and there 

 found a deposit of deep-blue or greenish clay, 12 feet thick, giving 

 the appearance of having in places been deposited in thin horizontal 

 layers, and therefore slowly, whilst at other spots it presented a more 

 conglomeratic character, and contained drift wood, pebbles, &c. Owing 

 to the difficulties attending the undertaking, and its satisfactory issue, 

 I never returned to daylight with greater satisfaction than on this 

 occasion. Having arranged for the removal of a quantity of the clay 

 to Bath, it was there subjected to a long examination, and resulted 

 in my obtaining a fauna in great part new to this country. 



Although certain that the deposit belonged to the Lower Lias, I was 

 then unable to determine with any precision the exact horizon it 

 would occupy when compared with any of the known stratified beds. 

 TLere can be little doubt that the Liassic seas at this period occu- 

 pied the profound depths of the Carboniferous-limestone fissures, 



