168 The Geology of the Berks 8f Hants Extension, 



swallow hole, the water from which considerably augments the 

 steam. There are several swallow holes near the junction of the 

 chalk with the Tertiary beds of Bagshot Hill, and Stripe Copse, 

 about one mile to the south. From one of these the water was 

 traced by the late Mr. Blackwell, who coloured the water as it was 

 swallowed up in the earth, and witnessed its reappearance at the 

 outlet at about the time expected. The underground course oi the 

 water in this case therefore, would appear to be in a more indepen- 

 dent channel than is usually considered to be the case in swallow boles. 



The cuttings near Hungerford Barracks' and Oakhill, are 

 through upper chalk, with a clayey gravel lying on its irregular 

 upper surface. These cuttings, and the one before mentioned, are 

 remarkable for an almost total absence of fossil shells. This is 

 however compensated for by the number and beauty of the sponge 

 spicules to be obtained from the hollow flints. They form good 

 objects for the microscope, especially when viewed by polarized 

 light. Foratninifera are also common in the fine chalk dust from 

 the inside of the flints. 



In the valley between Hungerford and Little Bedwin there are 

 many masses of pudding stone, consisting of rounded flint pebbles 

 in a base of ferruginous grit. This pudding stone is generally 

 referred to the Woolwich and Reading beds, and does not appear to 

 occur westward of Little Bedwin. There the ground is strewed 

 with blocks of Sarsen stone ; not the ordinary saccharoidal Grey- 

 wether sand-stone occuring on the downs, but the harder, finer 

 grained variety, of which the blocks in the Yale of Pewsey also 

 consist. The blocks are of irregular form, but rounded and smoothed 

 as if by the action of water, and are often pitted on what appears 

 to have been the upper and under surface, with small deep holes. 

 The holes are caused by the decay near the "surface of the stone, 

 of stem-like objects about the size of a large straw. In one of the 

 stones, the microscopic structure of these stem-like objects has been 

 well preserved. A transverse section, exhibits a centre about one 

 fortieth of an. inch in diameter, sometimes hollow, and sometimes 

 filled up, around which is a network of cells without any sign of 

 annual rings or medullary rays. A radial or a tangential section, 



