PART II. CHAPTER XVI. 



209 



Wealden Group Its Geographical Extent. 



198. 



Underside of slab of sandstone, about one yard in diame 

 ter ; Stammerham, Sussex. 



moulds, of which 

 casts have been taken 

 in relief, and which 

 are, therefore, seen 

 on the lower surface 

 of the sandstone* (see 

 Fig. 198.). 



Near the same 

 place a reddish sand- 

 stone occurs in which 

 are innumerable tra- 

 ces of a fossil vegeta- 

 ble, apparently Sphe- 

 nopteris, the stems 

 and branches of which 

 are disposed as if the 

 plants were standing 

 erect on the spot where they originally grew, the sand having 

 been gently deposited upon and around them ; and similar ap- 

 pearances have been remarked in other places in this formation.! 

 In the same division also of the wealden, at Cuckfield, is a bed 

 of gravel or conglomerate, consisting of water-worn pebbles of 

 quartz and jasper, with rolled bones of reptiles. These must 

 have been drifted by a current, probably in water of no great 

 depth. 



The occasional presence of oysters in the Purbeck limestone, 

 and throughout the Hastings sand and Weald clay, proves that 

 the waters of the sea sometimes found access into the estuary ,:{: 

 whether in consequence of subsidence, or in seasons when the 

 body of freshwater was lessened in volume. 



Geographical extent. The Wealden strata have been traced 

 about 200 English miles from west to east, from Lul worth Cove 

 to near Boulogne, in France, and about 220 miles from north- 

 west to south-east, from Whitchurch, in Buckinghamshire, to 

 Beauvais, in France. If the formation be continuous throughout 

 this space, which is very doubtful, it does not follow that the 

 whole was contemporaneous ; because in all likelihood the phy- 

 sical geography of the region underwent frequent change through- 

 out the whole period, and the estuary may have altered its form, 

 and even shifted its place. Yet some modern deltas are of vast 

 size, as for example, that of the newly discovered Quorra, or 



* Observed by Mr. Mantell and myself, in 1831. 

 t Mantell, Geol. of S.E. of England, p. 244. 

 \ Fitton, Geol. Trans., 2d Ser., vol. iv, p. 321. 



