458 Mr. Stark o?i the Sand-pipes in the Chalk near Norwich. 



hundreds of feet. For as the age of the chalk is undoubtedly 

 great, indeed beyond that of the superimposed strata, there 

 must have been a continued wearing away of the sides of the 

 cavities by the action of water, and a consequent transit of 

 the upper to the lower parts of the hollow, ages before the 

 clay, sand, and gravel were produced. 



The most remarkable part of Mr. Lyeli's paper is the fol- 

 lowing: he says, " It only remains for us to inquire how 

 waters charged with acid may most naturally be conceived to 

 have produced such hollows. If some of the largest pipes of 

 which the bottom has not yet been reached be prolonged in- 

 definitely downwards and connected with deep fissures, we 

 may suppose that springs charged with carbonic acid rose up 

 at some former period through the chalk and crag while they 

 were still submerged, as we know that in many parts of the 

 bed of the sea such springs do break forth. In proportion 

 as the chalk was corroded, the incumbent substances would 

 subside into the hollow thus formed and the water would freely 

 percolate the matter thus intruding itself, dissolving any cal- 

 careous ingredients which may be associated with it, and still 

 continue widening the tube by corroding its walls." 



Had this been the case, we may presume that the form of 

 the sand-pipes would have been exactly the reverse of what 

 they now are ; they would have assumed the form of cojies, but 

 not inverted co7ies; for the action of sucli waters must have 

 been greatest at the bottom where they first entered the chalk, 

 not only from the effect of mechanical force, but chemical ac- 

 tion ; and the destruction must have been greatest, and the 

 widening consequently largest, at the under part of such cal- 

 careous masses. 



Mr. Lyell seems rather to doubt this part of his hypothesis 

 himself, for he says it will not account for the form of the 

 greater number of sand-pipes, as they " have been found to 

 diminish gradually downwards to a point." 



This is precisely the form they would assume, supposing 

 that the fissures were produced, as I have stated ; the con- 

 tinued washing down of the upper parts of the chalk from 

 heavy rains, and streams of water of any kind, must have the 

 tendency to widen the upper part of each cavity, and pro- 

 gressively to fill up the lower part of it, by carrying down the 

 walls gradually from top to botton>, leaving portions of the 

 chalk in the transit of the fluid, and forming the smooth-sidpd 

 funnel-like shape that we now observe in the majority of 

 sand-pipes. 



The filling up of these pipes was undoubtedly an after 

 workf probably ages after; and the same cause that produced 



