232 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 18, 



the removal of the matter covering the chalk, without disturbance 

 of the surface of the rock. Until I drew attention to this fact*, they 

 had only been studied in sections ; and when seen in section, they 

 frequently present very deceptive appearances. 



It was the connexion of these furrows with pipes and other cavi- 

 ties in the chalk which caused me to venture to dissent from the 

 theory of their formation by acidulated water percolating the strata 

 above them, as promulgated by Sir Charles Lyell, and adopted by 

 some of our most eminent geologists. 



Detailed descriptions of several such cleared surfaces of chalk in 

 Kent and Norfolk, which I had watched from day to day, during 

 several weeks and even months, while the clearing was in progress, 

 will be found in the Proceedings and Journal. 



Shape of the Furrows and Pipes. — The result of these observations 

 was, that the furrows are, in some cases, wider than they are deep, 

 in others, deeper than they are wide, and that, in juxtaposition with 

 one another, and with both kinds of furrows, we find cavities of 

 various shapes, which all pass among geologists under the name of 

 pipes or sand-galls. There are cylindrical cavities of various depths, 

 some terminating abruptly, some extending below the depth of the 

 section, even when it is as much as 20, 30, and, in extreme cases, 

 nearly 60 feet. There are funnel-shaped cavities, or inverted cones. 

 There are caldron-shaped cavities, wider at half their depth than at 

 the surface, like many of the rock-basins on the sea-shore, or in the 

 beds of rapid rivers. There are dish-shaped cavities, or circular 

 basins, several feet in diameter, and not exceeding a foot or two 

 in depth. Lastly, there are large irregular cavities, such as would 

 have resulted from the breaking down of several neighbouring cavi- 

 ties into one. 



2. Occurrence of Pipes and Furrows in Non-calcareous Strata. — 

 The second argument in favour of the mechanical origin which I 

 assign to these mysterious excavations is, that they occur in non-cal- 

 careous strata. Dr. Fitton pointed them out in the Green-sand. 

 Before I saw them in that formation, I had observed similar pipes and 

 furrows, of much smaller dimensions, on blocks of sandstone derived 

 from the Lower London Tertiaries, and scattered over various parts 

 of Kent. A considerable number of these blocks were placed as a 

 protection to the footpath in the streets of Ospriuge and Feversham 

 in 1841, and some are still to be seen there. Some of the cylindrical 

 cavities in these blocks terminate in a blunt point, like those in the 

 chalk, others pass completely through the block. In a few blocks 

 they commence from opposite sides. I attribute this to the blocks 

 having been exposed to the breaking of the sea upon the shore, and, 

 after having lain for some time in one position, having been turned 

 over by a storm of unusual violence ; because — 



3. Pipes and Furrows now in course of formation on Stone and 

 Chalk — I had seen cylinders of still smaller size, on blocks of sand- 

 stone, on the shore near the Reculvers, actually being formed by the 



* Proc. Geol. Soc. vol. iii. p. 186; ibid. vol. iv. p. 7 and p. 482; and Quart. 

 Journ. Geol. Soc. vol. i. p. 300. 



