56 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



consists of an exceedingly tough calcareous, and at times sandy, clay 

 (fig. 4, d). Chalk in small fragments is abundant in it throughout ; 

 it contains also chalk -flints, some of great size, not much fractured, 

 though water-worn. The tenacity of this bed enables it to resist the 

 wash of the sea along the coast-line long after the overlying beds have 

 been removed. As to its mode of accumulation, it may be observed, 

 that it nowhere presents any indications whatever of horizontal ar- 

 rangement or bedding ; but that it is of marine origin is clearly 

 indicated by the shells it contains, such as Littorince and numerous 

 fragments of Mytili : these marginal forms are disseminated irre- 

 gularly throughout the mass. 



This accumulation is well seen between Aldwick and the entrance 

 to Pagham Harbour ; it occurs over the whole of the Selsea penin- 

 sula, and extends inland beneath the Sussex-levels for a considerable 

 distance : its upper surface is much eroded, and it has apparently 

 been thinned off much in the same way as has been noticed with re- 

 spect to the "mud-deposit" on which it rests. 



Independently of materials from the chalk-formation, there are 

 also occasionally fragments from oolitic strata, and of fossiliferous 

 chert-sandstone from the upper greensand ; but the great peculiarity 

 of this part of the series consists in the presence of rocks, which, 

 from their ages, composition, points of origin, size, and condition, 

 render its mode of accumulation a problem of no slight geological in- 

 terest. The rocks in question consist of grey porphyritic granites (these 

 are the most abundant), compact red granites, syenite, hornblendic 

 greenstone, mica-schist, green fissile slates, and fibrous chloritic semi- 

 crystalline rocks, masses of quartz from veins, siliceous sandstones, 

 such as those which occur in the palaeozoic strata (Lower Silurian) 

 of Normandy, coarse siliceous conglomeratic masses from the same 

 series, micaceous sandstones with Or f hides (Devonian), and black 

 micaceous shaly sandstones, perhaps from some coal-measure series. 

 With these are blocks of compact limestone, but whether mountain- 

 limestone, or from the older middle palaeozoic series of Devon and 

 the Cotentin, is as yet uncertain. 



Inasmuch as the upper surface of the yellow-clay deposit has 

 been much abraded, and must by such process have been made to 

 contribute materials to the beds above, some of the series of rocks 

 just enumerated are to be met with there also, as will be presently 

 noticed: their accumulation, however, belongs primarily, and perhaps 

 exclusively, to the period of the deposit now under consideration*. 

 Mr. Dixon notices them in Bracklesham Bayf. Sir R. Murchison 

 met with "a few pebbles of granite" in the lower marine beds 

 between Hove and Brighton X- 



The condition in which the old sedimentary or crystalline rocks 

 occur in the yellow- clay gravel-deposit is either that of perfectly 



* Crystalline rocks, in the form of '* rounded shingle," were first described by 

 Dr. Mantell beneath the "Combe rock" or "elephant-bed" near Brighton. — 

 Geology of the South-east of England, p. 32. 



t Dixon, Foss. Suss. &c. p. 14. 



X Quart. Journ. Geol. Soc. vol. vii. p. 396. 



