384 Mr. W. J. Sottas on the Flint 



Plate XVII. 



Fig. 1. Membranipora polita, n. sp. 



Fig. 2. Membranipora pedunculata, Manzoni. 



Fig. 3. Sehizoporella sanguined, Norman, var. 



Fig. 4. Microporella Jissa, n. sp. 



jFfy. 5. Porella roxtrata, n. sp. 5 a. Young cells showing the tridentate 



lower margin of the orifice. 

 Fig. 6. Membranipora corbula, n. sp. 

 Fig. 7. Mucrondla tubulosa, n. sp. 



XLVII. — On the Flint Nodules of the Trimmingham Chalk. 

 By W. J. Sollas, M.A., F.R.S.E., F.G.S., Professor of 

 Geology in University College, Bristol. 



[Plates XIX. & XX.] 



Personal. — In 1873 Mr. Jukes-Browne gave me some very in- 

 teresting specimens of flint nodules which he had obtained from 

 the chalk of Trimmingham, Norfolk. To the examination of 

 these I devoted a great part of the summer of 1874, preparing 

 some hundreds of drawings of the sponge-spicules which are 

 associated with them. After a visit to the Trimmingham 

 cliffs together, my friend Jukes-Browne and I arranged to 

 write a joint paper on them, he undertaking their general 

 geology and leaving the description of the flints to me. 

 Jukes-Browne's paper was ready for publication a year or 

 more ago; but mine seemed in danger of indefinite postpone- 

 ment, when I heard from Mr. G. Jennings Hinde, F.G.S., 

 that he too was at work on the same or a very similar sub- 

 ject. This led me to embody my results in the following 

 paper, which was read before section C of the British Asso- 

 ciation during its meeting at Swansea this summer. It will 

 appear as an abstract in the Annual Report, and is given here 

 in full as a sequel to Mr. Jukes-Browne's, which appeared in 

 the ' Annals ' of last month. 



The Flint Nodules. — In form they vary greatly : some are 

 flabellate, some irregularly conical ; others consist of a some- 

 what ellipsoidal body seated on a short stalk, while many are 

 irregular and amorphous. They consist of chalk and silex in 

 various proportions ; sometimes the chalk forms the greater 

 part of a nodule, sometimes it is altogether absent. Between 

 a nodule consisting of a solid mass of silex, black throughout, 

 except on the surface, and one consisting chiefly of siliceous 

 chalk there are any number of others forming a complete 

 transitional series. Commonly the flint is traversed by a 

 number of winding anastomosing passages, which are occu- 



