DEPOSITS 1ST THE BRISTOL DISTRICT, 



71 



fringe the outcrop of the older rocks, but high up on their table- 

 lands, as in the case of the Charterhouse lead-mine, near 

 Cheddar. 



The Bristol Area. 



Before proceeding with a description of the Bristol area and 

 comparing it with the above, it is desirable I should advert to a new 

 palseontological feature which hitherto has not attracted any atten- 

 tion, in the presence of a multitude of minute Serpula-Mke calcareous 

 tubes found in various deposits under examination. Tears ago I 

 noticed them in the freshwater brick-earth of Salisbury, which is of 

 Postpliocene age, and put them aside as minute Serpulce ; but after- 

 wards learning that all species of this family are marine, I thought 

 they might possibly be analogous to caddis-cases, and belong to some 

 insect. When they were afterwards found in enormous numbers, 

 and under many diverse circumstances, I saw the desirability of 

 learning more about them, and sent them to friends who were 

 authorities in special departments of natural history for their 

 opinions, at the same time describing the circumstances under which 

 they were found. Without mentioning names, it proved a " pursuit 

 of knowledge under difficulties." First, they were doubtfully re- 

 ferred to the cases of some Dipterous insect ; and if not such, it would 

 be worth considering if they were Serpulce. An entomologist decided 

 that they were not insect-tubes ; a good microscopist was of opinion 

 they were the calcareous cases left by rootlets of vegetation passing 

 down from the surface ; next, an eminent zoologist intimated, with 

 some uncertainty, that they somewhat resembled the genus of Ser- 

 pulidse, Filograna ; then a good botanical friend and microscopist 

 pronounced them to be vegetable ; upon which I sent them to a 

 first-class botanical expert, who was of opinion they had nothing 

 to do with vegetables, and that he had consulted a zoological friend, 

 who also believed they were worm-tubes allied to Annelids, and 

 that again they presented some resemblance to Filograna. 



They are to be found very abundantly in some of the vein- 

 fissures of the Carboniferous Limestone (to be referred to hereafter) 

 in the Bristol district, and also, though not in such numbers, in 

 some of the later stratified marls. My impression is that they 

 are due to freshwater conditions, and that, though they may not 

 be rootlets which have passed down from the surface (some of 

 them being found under conditions apparently precluding this idea), 

 yet they may, notwithstanding, be due to freshwater vegetation. 

 They are sometimes free, but often in clusters united by the ma- 

 trix of the deposit. It will be desirable to determine their syste- 

 matic position, as they will have a bearing on the age and other 

 conditions of the deposits in which they are found. I propose 

 that they should be recognized under the designation of Tubutella 

 ambigua. 



Durdham and Clifton Doivns. — I now propose to show that the 

 same physical conditions prevail at Durdham Down and at various 

 outlying spots near Bristol, as in the Frome district. The area to 



