66 REPORT — 1839. 



chalk beneath the gravel is very irregular ; in some places tubular 

 hollows, having the form of inverted cones and filled with sand and 

 gravel, extend downwards into the chalk. They vary in width from a 

 few inches to eight yards and upwards, and in depth from a few feet 

 to more than sixty. Some are tortuous, but most of those at Eaton, 

 near Norwich, are perpendicular. The materials filling the pipes agree 

 precisely with those covering the chalk, with the exception, that in the 

 pipes they are unstratified. The pebbles in the gravel consist of 

 rounded flints and quartz ; but no shells or pieces of chalk, or any 

 calcareous substance, occur in the pipes. In general, coarse sand and 

 pebbles occupy the central part of each pipe, while the bottom and 

 sides are lined with a fine ferruginous clay, destitute of calcareous 

 matter, but permeable by water. The chalk for a short distance ai-ound 

 the sandpipes is moist and softened, and slightly discoloured by an in- 

 termixture of clay. Further from the pipes it is white and perfectly 

 soluble in acids. Those pipes, whose diameter is less than a foot and 

 a half, are often crossed by horizontal layers of flint nodules, which 

 have remained in situ, while their chalky matrix has been removed. 

 The author hence infers, that the pipes were formed by the corroding 

 action of water containing acid. But it is clear that the tubes were 

 not first excavated to their present size, and then filled with gravel, 

 for in that case the nodules of flint derived from the chalk would have 

 fallen to the bottom of the larger cavities, — but this never happens, 

 the larger flints being always dispersed irregularly through the sand 

 and gravel which fills the tubes. Mr. Lyell therefore infers that the 

 excavation and filling of the tubes proceeded contemporaneously and 

 gradually, and that thus the flint nodules, when removed from their 

 matrix, subsided upon the sand and gravel which had previously sunk. 

 This is further proved by the fact, that the horizontal strata of gravel 

 are sometimes seen to bend down into the mouth of a pipe, and there 

 become vertical. Mr. Lyell is of opinion, that some of the larger 

 tubes (if not the smaller ones also) have been caused by springs 

 charged with carbonic acid, rising through the chalk. The fine layer 

 of clay, which coats the surface of the tubes, may have been deposited 

 by the percolation of rain-water at a later period ; and some of the 

 finer particles, being carried into the chalk itself, would cause the dis- 

 coloration of that rock near the pipes. 



It was further stated by J. B. Wigham, Esq., in a letter to Mr. Lyell, 

 that examples of slanting and tortuous sandpipes occur near Heigham. 

 At Thorpe there is a pipe which penetrates both the chalk and the 

 superincumbent crag, the whole being covered with the usual gravel. 

 The clay lining is found throughout, and over this lining is a thin 

 stratum with impressions of shells. Near Norwich many springs come 

 up in the chalk, and sandpipes are always found near them*. 



* For a fuller statement on this subject, with illustrations, see Phil. Mag., 

 No. 96, p. 258, October 1839. 



