Geological Society/, 509 



Holes, near Farnham ; with some observations on the drainage of the 

 country at the western extremity of the Hog's Back," by Henry 

 Lawes Long, Esq., and communicated by C. Lyell, Esq., V.P.G.S. 



Farnham stands at the foot of the chalk hills, upon a deep bed of 

 loam, which appears to overlie the gault. Upon the chalk, imme- 

 diately to the north of the town, is the castle, beyond which the 

 tertiary strata commence and rise to a considerable height, forming 

 the great mass of hill known by the name of Farnham Beacon, Tun- 

 bury, or the Lawday House. On the north side, this hill presents, 

 for the greater part, an abrupt precipice, under which several sti'eams 

 are thrown out ; but on the south there are landsprings only, which 

 occupy the gulhes for the greater portion of the year, and occasion- 

 ally become formidable torrents. These rivulets pcur down the 

 tertiary clays until they arrive at the chalk, where they plunge into 

 the ground and disappear, except during very hea\'y rains, when 

 the surplus waters are carried off by gravely channels in the chalk. 

 The principal object of the paper is to describe the seven swallow 

 holes between Clear Park and Farnham Park, and a minute account 

 is o-iven of each. They occur in Clear Park — Lower Old Park Gully — 

 Clay-pit Gully — near the Potter's Clay-pit — in the Hop-grounds, 

 above the turnpike a little west of the Odiham-road — near the en- 

 trance of the pleasure ground in Farnham Park — and near the end of 

 the avenue at the east of Farnham Park. The water absorbed by the 

 holes in Farnham Park is supposed to reappear at the Bourne -Mill- 

 stream ; and though soft where it sinks into the chalk, it is hard and 

 unfit for use, where it again breaks forth. The existence of under- 

 ground currents was further proved by a well sunk at Hale Farm, 

 which gave the following section : 



Sand and gravel 6 feet. 



Clay (potters') 15 or 16. 



Sand and gravel 20. 



Clay (potters') 14 or 15. 



Clav, blue (London?) lowest 2 feet a green sand 24. 



Hard chalk 20 or -30. 



At that depth a spring was reached, which was supposed to be the 

 Bourne-Mill-stream, and the instrument went down rapidly many 

 fathoms, through a chalk mud. The well-sinkers afterwards came 

 upon chalk with many flints, and finally breaking their instrument, 

 left SO feet of it in the earth, having bored altogether to a depth of 

 17G feet. 



Tlie green-sand tract, described in the second part of the memoir, 

 and drained by a stream which flows northward through a gap in 

 tiie chalk at Runfold into the London basin, is bounded on the north 

 by the straight line of the Hog's Back, and on the south l)y a semi- 

 circular range of the low hills extending from Scale on the east by 

 Crooksbury Hill to Moor Park on the west. The surface of the tract 

 being sandy and naturally bibulous, tiic proprietor of the farm has ren- 

 dered it more retentive by a system of marling, and tlie rain water 

 being consetjuently less absorbed than formerly, it is collected in an 

 excavation called White-ways End Pond, at the western end of the 



