xvi 
SELBORNE. 
and, if the malm or the rag is near the surface, it is so full of 
shakes and fissures that the water descends to such a depth 
that there are no runs even in the deep lanes, except such 
as are produced by showers upon the surface. In his nineteenth 
letter to the Hon. Daines Barrington, Mr. White expresses him- 
self a little puzzled about the different rates at which ponds dry 
in different situations, the small ones on the heights being more 
permanent than the large ones in the hollows. Now these small 
upland ponds are on the chalk, while those lower down are on the 
clay, the malm, or the sand, the latter being especially the case 
with the large pond in Wolmer Forest. On the chalk near its 
surface the pond has a chance of receiving some water through 
the soil in those parts of the down which may be higher. On the 
clay this is not the case, because a stratum of stiff clay does not 
allow water to pass, but either over it or under it. There can, 
therefore, be no spring in a clay pond which can afford it any 
supply ; and consequently, when the surface supply is cut off, 
such a pond can retain water no longer than the evaporation re- 
quires to carry off the store contained in it. 
In the case of ponds over the malm and the sand, it is some- 
what different. Neither of these would naturally form a pond 
capable of retaining water ; and thus they become retentive only 
by the fine particles being carried into them, and lodged there by 
the rain and wind, until the hollow is lined with a water-proof 
stratum, and thus becomes capable of retaining a supply. But 
there can be no supply from springs in such a pond, any more 
than there can be in a pond on the clay ; because, while the clay 
will not allow the water to get in, the shivery rock or the sand can- 
not prevent it from sinking downwards. These are the real causes 
of the difference in drying up between the ponds of the high and 
the low grounds about Selborne, and of course they hold in all 
other places where there are similar differences in the sub-soil. 
In order to complete the view of the different localities of Sel- 
borne, it is necessary to take a peep from the top of Selborne 
Hill, as near the margin of the Hanger as possible. This, how- 
ever, is a bird's eye view, the point of observation being the highest 
of the whole, and therefore the diflferent objects have little pic- 
torial relief ; and, though the details are better seen than from 
almost any other point, yet there is no general impression so 
striking as to be easily remembered. From the top of the hang- 
