PRESTWICH — SAND- AND GRAVEL-PIPES. dj 



the pipe, as well, or I should conceive, better than the action of the 

 sea on a shore ; for in the former case the water would keep to any 

 given channel more constantly than in the latter. 



2nd. Mr. Trimmer states that many of the flints are water-worn. 

 This is not sufficient : the majority, or rather all those at the bottom 

 of the pipe, should be water-worn, and all should show more or less 

 wear ; whereas the majority in general, and those especially on the 

 sides and at the bottom, are decidedly not at all water-worn ; on 

 the contrary, they are always at least as sharp and angular as those in 

 the superincumbent strata, and often as those in the Chalk itself. 

 That flint pebbles and worn subangular flints do occur in these pipes, 

 cannot be doubted ; but the former are derived from the Tertiary 

 strata (a fact to which Mr. Trimmer himself makes allusion), and 

 the latter are from some of the beds of drift-gravel. 



3rd. When we consider that these pipes are often 20, 40, or 

 even 60 feet or more deep, with an average diameter varying from 

 about ^ to 3^ of their depth, an apex of 3 to 4 inches (it is sometimes 

 more and sometimes less than that) can hardly be objected to as not 

 being such a point as we might expect to be caused by the infiltration 

 of water. If the water escaped through a single point only, as in 

 the tube of a funnel, the argument would be good ; but as the whole 

 body of chalk is porous and soluble, we can readily conceive the 

 apex of the tube to be more or less sharp or blunted according to 

 various conditions of the chalk. The chalk, in fact, is the filtering 

 material and not merely the filter-holder, and the water passes in a 

 body downwards by the ordinary laws of hydraulics, and is not other- 

 wise directed by any mechanical arrangement to one particular point. 

 4th. Mr. Trimmer states that the Tertiary sandstones on the 

 shore at the Reculvers are not calcareous, and that they, as well as 

 other blocks scattered over North Kent, show traces of hollows worn 

 out by the sea. On this point there is apparently some mistake 

 with respect to the Reculver sandstones, for I have found them 

 readily acted upon by dilute acids and containing a considerable 

 proportion of carbonate of lime ; those, however, scattered over the 

 surface near Faversham are certainly purely siliceous, but then also 

 they are concretionary, and as usual in such cases they present 

 very irregular and often mammillated surfaces, with numerous small 

 natural hollows and cavities on either side. But even if these latter 

 were holes worn by subsequent sea-action, I do not see the force of 

 the argument which compares indentations and furrows to be mea- 

 sured by inches with the comparatively gigantic ones we are deahng 

 with in the Chalk. 



5th. The Thanet Sands near Canterbury can scarcely be called iu 

 any degree calcareous. I have examined several specimens, not only 

 from that locality but also from other parts of Kent, and have found 

 that the great majority of them, especially those forming the lower 

 beds of this deposit, show scarcely a trace of carbonate of lime, and 

 that they are composed essentially of siliceous sands more or less 

 argillaceous. The shells which occasionally occur in some of the upper 

 beds of these sands near Canterbury have almost all been dissolved 



f2 



