1854.] TRIMMER ON SAND-PIPES. 233 



vorticose action which the flux and reflux of the waves communicated 

 to sand and water lodged in hollows on the face of the block : 



4. I have seen cylindrical and funnel-shaped cavities connected by 

 furrows, in the course of formation by means of similar vorticose 

 action, on a flat shore of chalk, between high and low water, near 

 Cromer. The cylinders were 2 inches in diameter and 4 inches deep. 



5. After the heavy gale which, in 1846, carried away the jetty at 

 Cromer, and caused great destruction of the detrital cliffs there, I 

 found part of a ledge of chalk, which forms their base, and which 

 had been exposed for some little time to the breaking of the sea 

 beyond the usual tidal limits, having a surface of several square 

 yards, covered with circular hollows, I to l^^foot in diameter. These 

 cavities were filled with loose pebbles, on removing which, the 

 cavities were found gradually to contract in diameter, until they as- 

 sumed a cylindrical shape. A section of one, laid open by the sea, 

 was 2 feet deep and 3 inches in diameter, terminating with a blunt 

 point, like many larger chalk-pipes of other epochs. This is a very 

 common depth of similar cavities on various strata which are filled 

 with warp-drift, as I shall describe hereafter, and which rarely attain 

 the large size so common among those in the chalk which are filled 

 with older tertiary deposits. 



6. Conformability or Non-conformability of Deposits overlying 

 the Mouths of the Pipes. — On a broadly-undulating surface of chalk, 

 covered with the crag, the ferruginous breccia, called " the pan," 

 which forms the base of that deposit, together with the alternations 

 of sand and clay above, conform to this undulating surface. It is the 

 same with those large irregular cavities v/hich have a greater width 

 than depth. Such conformability to an irregular surface is admitted 

 by geologists to be an original condition of deposit ; and that bending 

 down of the strata into the mouth of a pipe of considerable diameter, 

 which has been adduced as a proof of subsidence, may be only an ex- 

 treme case of conformability to an irregular surface. 



7. Above this irregular stratification, there are alternations of sand 

 and clay over the pipes, which are perfectly horizontal. 



8. It is only over pipes of large diameter that there are those irre- 

 gularities of stratification, which have been supposed to indicate sub- 

 sidence. 



9. Occurrence of calcareous matter in the Pipes. — In the deeper 

 furrows connected with the pipes, we find alternations of deposit 

 distinct from the superincumbent strata ; and among these are layers 

 of fragmentary chalk, which acidulated water, percolating from 

 above, ought to have dissolved before it could have excavated the 

 furrow. 



10. Pipes in inclined strata. — The pipes on the surface of the 

 tilted chalk of Alum Bay must have been formed before the disturb- 

 ance ; for they are perpendicular to the original plane of stratifica- 

 tion, and, when the chalk was horizontal, the sands above it were 

 covered by the impermeable mass of the mottled clay. The position 

 of the strata now is highly favourable for the downward percolation 

 of water, but no new pipes are being formed on the inclined chalk. 



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