426 NATURAL HISTORY OF SELBORNE 



Upper Greensand, saturated with water, held up by the under- 

 lying Gault Clay, sliding forward over the slippery surface of that 

 deposit. Even where extensive slips have not occurred, the ground 

 near the edge of the Greensand area is often broken owing to 

 slight displacements due to the same cause. 



The upper part of the Upper Greensand (the " White Malm " 

 of White), in this neighbourhood consists of alternations of blue 

 ragstone, which is a hard argillaceous rock, and " firestone," which 

 is a sandstone much used for hearthstones and oven-beds, as 

 described in Letter IV to Pennant, where also the ragstone is 

 mentioned as being used for a variety of purposes. These upper 

 beds are well exposed in the side of some of the " hollow lanes " 

 so characteristic of the neighbourhood. These are sometimes 15 to 

 20 feet deep, and seem to have been produced originally by the 

 wear of traffic, but afterwards this has been assisted in deepening 

 them by the water which runs along them after heavy rains. 



The thickness of the Upper Greensand must be rather over 

 60 feet, for White mentions that the wells at Selborne are on the 

 average about 63 feet deep, and the water is no doubt held up by 

 the underlying Gault Clay. This latter deposit is exposed along a 

 belt from half a mile to about a mile in width to the east of the 

 Upper Greensand escarpment. It also appears along the lower 

 part of the valley of the Oakhanger stream, which has cut down to 

 it through the Upper Greensand beds as far as a point about a 

 quarter of a mile east of Selborne Church. To the east of the 

 Gault again we meet with the sandy beds of the Lower Greensand, 

 which form the open furze and fir-clad heaths of Wolmer Forest 

 and the neighbourhood. These sands seems to contain much water, 

 which, in the lower ground, forms pools, of which Wolmer and 

 Oakhanger Ponds are good examples. 



White makes several references to the occurrence of fossils in 

 the rocks of the neighbourhood. The shell which he figured and 

 describes under the name Mytilus crista-galli is the Alectryonia 

 ricordeana, Coquand (Ostrcea carinaia, Lamarck), from the Chalk 

 Marl. The Cornua Ammonis, which he speaks of as being found 

 in making the path up the Hanger, must consist of Ammonites 

 from the Lower Chalk; while the Nautili from the north-west 

 of the Hanger are probably the Nautilus elegans of the Chalk 

 Marl. Other species from this last-named deposit are Schlcenbachia 



