Notices of Memoirs — J. J. H. Teall — Dedohmitisation. 513 



very stout tail. The pectoral fins were relatively large, with almost 

 sickle-shaped spines, while the pelvic fins were rather small, with 

 straighter spines, and situated very far forwards. There were two 

 pairs of peculiar free spines near the base of the pectoral fins. The 

 two dorsal fins and the anal fin were provided with much smaller 

 spines. Gyracanthides was evidently one of the most, highly 

 specialised Acanthodians, and showed that among these primitive 

 fishes, as among modern Teleosteans, there was a tendency for the 

 pelvic pair of fins to become displaced forwards in the higher types. 

 The author had already described the same phenomenon in the 

 typical family Acanthodidee. 



IV. — Land-Shells in the Infra-Glacial Chalk-rubble at 

 Sewerby, near Bridlington.^ By G. W. LAMPLuan, F.Gr.S.^ 



THE Chalk-rubble which underlies the glacial drifts of Flamborough 

 Head has not hitherto been known to contain organic remains. 

 In a recent exposure of this material on the foreshore between 

 Bridlington Quay and Sewerby the writer found numerous small 

 fragile land-shells contained principally in intercalated streaks of 

 brown earth. These shells belong mainly, if not entirely, to the 

 species JPnpa miiscortim, Linn. The level at which they were found 

 was about 8 feet below the top of the Sewerby Infra-Glacial sea- 

 beach, and the Chalk-rubble is known to descend to at least 25 feet 

 below this level. 



The rubble usually rests directly upon the Chalk, but at Sewerby 

 it overlies the Infra-Glacial blown-sand which is banked against 

 the buried cliff of chalk. The presence of the land-shells proves that 

 the rubble is a subaerial rain wash, and that it was formed when 

 the sea stood at a lower level than when the Infra-Glacial beach 

 was deposited. The conditions thus indicated are strikingly similar 

 to those which obtain in the deposits associated with the Infra-Glacial 

 buried shores of South Wales and co. Cork, where the old marine 

 beaches and the accompanying blown-sand are covered by local 

 rainwash or ' head,' and then by Boulder-clay. 



The Chalk-rubble at Sewerby contains many small pieces of flint, 

 though no flint is present in the Chalk within two miles of this 

 locality ; a few small fragments of yellow grit or quartzite foreign 

 to the neighbourhood, along with one subangular boulder of similar 

 rock 18 inches in diameter, were also found in it. Part of the 

 material was probably deposited almost immediately before the 

 glaciation of the district. 



V. — On Dedolomitisation. By J. J. H. Teall, M.A., F.R.S., 



Director of the Geological Survey.^ 

 rj1HE Durness dolomites, as they approach the plutonic complex of 

 X Cnoc-na-Sroine, become transformed into a white marble which 

 generally contains one or more of the following minerals : forsterite, 



1 The full text of this paper will be published in Proe. YorJcs. Geol. and Polytech. 

 Society. 



2 Abstract of paper read before the British Association, Southport, Section C 

 (Geology), September, 1903. 



DECADE lY. — VOL. X. NO. XI. 33 



