302 Messrs. Buckland's and Conybeare's Observations on the 



eastern frontier of the Bristol coal-basin, in the road ^ a mile to the east of the 

 town of Wickwar. 



All the organic remains, which are commonly found in the lias in other 

 parts of England, occur also in the district here treated of. Near Twiverton 

 and Keynsham have been discovered the Ichthyosaurus and the Plesiosaurus, 

 large compressed fishes, Crustacea of the crab and lobster kind, and the beaks 

 of Sepiae. Mr. Miller of Bristol has in his collection from the bone-bed at 

 Aust Passage many large tuberculated bodies, extremely compact, and of a 

 jet-black colour, which were probably connected with the palates of some very 

 large cartilaginous fishes. The lias of our district affords all the Testacea 

 most common to the formation, especially Gryphites, the gigantic Plagiostoma, 

 and enormous Ammonites, which at Keynsham have given rise to the same 

 romantic legends respecting the miraculous powers of St. Keyna, as have 

 prevailed concerning St. Hilda at Whitby. Several species of Pentacrinite 

 also occur, one of which found at Pyrton passage and at Frethern cliff is not 

 common. 



In tracing the geographical extent of this formation, we find it to the south 

 of the Mendips reposing on the newer red sandstone, which extends beneath 

 the marsh-lands of Somersetshire, the lias probably itself also forming a part 

 of their substratum. Occasionally it emerges above them, and then composes 

 the summit, or, in some cases, the entire mass of several insulated hills, which 

 are sufficiently indicated in the Map [PI. XXXVIII.], and in the Sections 

 [PI. XXXII.]. The most remarkable of these is Brent Knoll, which, rising 

 to the height of 470 feet above the sea, and standing quite alone amid the 

 marshes, presents a very conspicuous land-mark. 



Towards the eastern extremity of the Mendip chain, and to the south of it, 

 at Pennard and Glastonbury, the lias is but little elevated above the marshes ; 

 but, by rising constantly though imperceptibly towards the north, it acquires 

 a considerable height to the north of Shepton Mallet. Here it rises more than 



Dapedium politnm, plate vi. fig. 4. Geol. Trans., vol. i. 2nd series; there are also flat bony 

 substances, studded with small tubercles such as belong to the head of that fish. 



4. Bones (or fragments of bones) for the most part small, black, and very compact; belonging 

 apparently to some small reptile. Among these only one vertebra has been found. 



There occur also many irregular bodies, varying much in form and substance, which are usually, 

 however, cylindrical with rounded ends, some having a black and glossy surface and fracture, 

 others being of a dull-brown colour. They are probably rolled palates, or rolled fragments of 

 very solid bone. 



Fish-bones are here of rare occurrence in comparison of spines, teeth and palates; which cir. 

 cumstance perhaps may be accounted for by reason of the soft and perishable nature of the bone 

 of the cartilaginous fishes, to which the spines, teeth and palates belonged. 



