1854.] PRESTWICH — STOKE NEWINGTON GRAVEL. 109 



caused the extension of this deposit itself over the lower gravel (c?), 

 — that is to say, it was neither the flooding of a previously dry sur- 

 face by the waters from which the shelly clay was afterwards depo- 

 sited, nor was it by the detrital sweep of the upper gravel over this 

 later area of water and dry land that the trees were destroyed. 

 Their presence must, on the contrary, be due to some common cause 

 in common operation during the whole period that the freshwater 

 mollusks were living undisturbed in these waters. One cause might 

 be occasional floods ; although in that case we might have expected 

 a greater change in the sediment, arising from the greater trans- 

 porting power of the water, — the trees to have been more in seams, 

 more of them showing uprooting, and more entire. Whereas the trees 

 are in fragments, their branches and stems are sharply broken into 

 short pieces, lying about without order, all prostrate, and in a 

 sediment showing little or no change. I conceive such a result to 

 have arisen partly no doubt from this cause, but probably chiefly 

 from the occasional breaking off of boughs and the smaller stems of 

 trees on the margins of these pools or meres, during gales of wind, 

 which scattered them and the leaves over the surface of these waters, 

 where they sank and got buried vrith the Planorbis, LimncBus, 

 Pisidium, &c. The texture of the wood is generally but very little 

 altered, and its colour is often almost unchanged. When dried, 

 it becomes extremely light. 



The bones were found at the base of the shelly clay, and con- 

 sisted of part of the trunk of some large mammal (Ox?)* ; nine ver- 

 tebrae and some of the bones of the legs were found together, but 

 the skull was missing ; nor, notwithstanding the diligent search 

 established by Mr. Hindle and Dr. Beeke for several feet around, 

 could we succeed in obtaining any further remains of this animal. 

 Unlike the wood, the bones were much mineralized and very heavy. 



The evidence afforded by the remains of this animal agrees with 

 that afforded by the remains of the vegetation. The bones were 

 tranquilly imbedded in the mud of a freshwater deposit, the animal 

 probably having after death floated on the surface of the waters, 

 the bones subsiding here and there as the carcase decayed and fell to 

 pieces ; for it must be observed that the bones show no traces of wear 

 or fracture, — nothing to denote violence or distant transport. 



Under the clay (c) is found a bed of gravel and sands, some light- 

 coloured and others ferruginous, in the upper part of which shells, 

 I was told, similar to those found in the clay have occasionally been 

 found ; I however met with none. This gravel consists of subangular 

 flints chiefly, with a few flint-pebbles ; not enough of it was dug up 

 to notice whether there were any pebbles of the secondary rocks. 

 Its thickness is not shown here ; but as the London Clay comes out 

 on the side of the adjacent Hackney Brook on a level a few feet 

 lower, I do not think it can exceed 6 to 10 feet. 



The shells procured from the deposit we have here described, pre- 

 sent a general close agreement ^\ith those found in the Salisbury drift 

 (see p. lOG), except that the group of marsh and pond shells is more 

 * The bones unfortunately have been mislaid. 



