232 
Ist series, vol. iv. p. 413. pl. 24., is still involved in much obscurity. 
Their form is most probably due to siliceous matter collected around 
and penetrating throughout the substance of gigantic spongiform 
bodies ; but we have yet to learn the reason why they are occasion- 
ally placed in single vertical rows, almost like the joints of a basaltic 
column, sometimes nearly touching, but not articulating with one 
another. 
A paper has been read by Mr. Henry Lawes Long on the occur- 
rence of numerous subterraneous chasms or swallow-holes in the chalk 
on the west of Farnham, with observations on the drainage of the 
country near the west extremity of the highly-inclined ridge of chalk, 
called the Hog’s Back, between Guildford to Farnham. The land- 
springs immediately on the north of Farnham descend southwards 
in open gulleys over tertiary strata, until they arrive at the narrow 
band of chalk which passes under Farnham Park, where they are 
suddenly engulphed in transverse fissures or swallow-holes, through 
which they pass under ground to a considerable distance, and again 
break forth on the southern side of the chalk. Seven of these 
swallow-holes occur near Farnham, from some of which the water 
emerges in sufficient force to turn a mill. They are probably con- 
neeted with subterranean faults and transverse fractures, the origin 
of which was coeval with the elevation of the narrow band of chalk, 
which forms the Hog’s Back, and which, near Farnham, is inclined 
at a high angle to the north. The water that now passes through 
the Farnham swallow-holes may tend to enlarge the chasms through 
which it takes its subterraneous course, by dissolving slowly the 
chalk of their sides in the small quantities of carbonic acid which 
rain-water usually contains. 
Similar transverse fractures, on a greater scale, have given origin 
to the chasms, which, being enlarged by denudation into transverse 
valleys, afford outlets through the high escarpment of the chalk to 
the rivers that, rising within the Weald, flow through the escarpment 
of the north Downs into the valley of the Thames, and through the 
escarpment of the south Downs into the sea, viz. to the Wey, the 
Mole, the Darent, the Medway, and the Stour, through chasms in 
the north Downs; and to the Arun, the Aduz, the Ouse, and the 
Cuckmere, through chasms in the south Downs. 
Dr. Mitchell has communicated a paper on Artesian and other 
