392 Correspondence — Mr. Alfred Tylor. 



serai-aquatic plants grew, affording shelter for the land snails, which 

 inhabit usually marshy or damp situations ; Ziia lahrica, however, 

 is more sylvan in its habits, than the others. All the species inhabit 

 Great Britain, but ClausiUa bij)licata ranks amongst our rarest. — E.T." 



In 1866, during the formation of a cutting through Hackney 

 Downs, Mr. S. Skertchly made a large collection of Thames Valley 

 drift-shells which he discovered there, and brought me a series 

 which were named by Mr. K. Tate. I understand Mr. Skertchly 

 also sent a set of specimens to Mr. Smith at the same time. In 

 July, 1867, a notice of the discovery of these shells appeared 

 in the Natural History Repertory, by Mr. George J. Smith. I 

 inspected the section in 1866, and found that the Unios were 

 in a bed of purple clay with sands above and below them. 

 The surface of Hackney Down is 70ft. above the Ordnance datum- 

 line, and the Cyrena and Unio bed, although partly covered up 

 when I examined it in 1866, appeared to be, at least, 20ft. below 

 the surface. The Hackney Brook formerly flowed 550 yards west 

 of the above Cyrena bed on Hackney Down at a height of 

 51 feet above the Ordnance datum-line. I consider that in this 

 part of its course the channel of Hackney Brook was on tliis same 

 Pleistocene clay, which is three or four feet thick, and not in London 

 Clay, as marked in Mr. R. W. Mylne's Map of London. 



The discovery at Hackney Downs of a clay-bed with shells re- 

 minds us of the description of a similar section at Shacklewell by 

 Mr. Prestwich in Yol. XL of the Quarterly Journal of the Geo- 

 logical Society, at a locality not far distant from Hackney Downs. 

 The clay-bed is described there to be between beds of sand ; but 

 neither Cyrena nor Unio are in Mr. Prestwich's list of fossils from 

 that excavation. Sir C. Lyell, however, states in the " Antiquity of 

 Man," that he had seen Cyrena at Shacklewell, page 161. 



Cyrena and Unio are found together in great abundance at 

 Grays, Crayford, and Hackney Downs. Mr. A. Harris, of Bradford, 

 brought me, in 1867, a number of specimens of the same Cyrena, 

 accompanied by an undescribed but remarkable species of Unio from 

 a Pleistocene gravel 150ft. above the present Nile, and 1200 miles 

 from the Mediterranean. I use the name Cyrena as more familiar 

 than the term Corhicula, by which it is often recorded. 



I should hope that shells may yet be found in the larger and older 

 brick-pit in Highbury. The smaller brick-pit in Highbury New 

 Park is easily found, as it is about one hundred yards west of the 

 bridge over the New Kiver in the Green Lanes, Stoke Newington, 

 close to Aden Terrace, and about four hundred yards east of Highbury 

 Barn Tavern. No doubt a considerable addition might be made to the 

 number of species collected by me, and it is therefore very desirable 

 that the spot should be carefully examined before it is filled up. — 



Alfred Tylor. 

 Stoke Newington, Jul^ 5, 1868. 



