XXVUl PROCEEDINGS OF THE 



of the canal brought the party to the first of the large chalk-pits to 

 be visited, on the left bank of the river. The Upper Chalk here 

 is bare, and of a pure white, the clayey beds which come on 

 just above having thrown off the water falling upon them, thus 

 preventing it from precolating into the chalk and giving rise to 

 pipes. 



The next pit, a field's length farther south, by the old " Copper 

 Mills " which have long ceased working, was soon reached, and 

 formed the principal point of interest. Here the whole section of 

 the chalk, which presents an almost vertical cliflt from 90 to 100 

 feet high, is irregularly capped by gravel, from which pipes, often 

 of most fantastic shape, and of roughly cylindrical form, extend 

 downwards to distances varying usually from 30 to 70 feet. A 

 mass of white chalk, of such a height and extent as, but for those 

 pipes, would here have been exposed, would have had a most 

 dazzling appearance ; but the whiteness of the chalk is subdued 

 by the darker colour of the pipes, which appear to occupy almost 

 as much space on the surface of the vertical sides of the pit as 

 the chalk itself. 



Here Mr. Whitakcr, mounting a tilted truck, explained the mode 

 of origin of these pipes. They were, he said, holes or hollows in 

 the chalk filled in by gravel or sand from the beds above. In old 

 books they were sometimes stated to have been formed by sea- 

 action, but such was not the case. They were caused by rain, 

 which, in passing through air, absorbed carbonic acid, a gas which, 

 in solution, had the power of dissolving the hardest limestone. 

 The water, charged with carbonic acid gas, sank down through 

 some line of weakness in the chalk, along which it gradually dis- 

 solved the rock, until at last the overlying gravel and sand sank 

 into the cavity thus formed. Here and there a mass of gravel was 

 to be seen which appeared to be unconnected with the pipe im- 

 mediately above it, this appearance being due to the chalk not 

 always having been worn away in a vertical line, so that the 

 connecting-link of the pipe was not to be seen ; and this was the 

 explanation of the apparently isolated masses of gravel frequently 

 seen in the chalk. "Where there was a mass of Tertiary clay on 

 the chalk, there were generally no pipes, for the clay being im- 

 permeable prevented water from getting through into the chalk ; 

 whereas water percolated through gravel, forming these pipes, in 

 which might frequently be seen angular chalk-flints, not worn at 

 all, and nearly in the position they occupied before the chalk in 

 which they were embedded was dissolved away. The gravel here, 

 Mr. Whitaker stated, forms part of a high terrace that occurs over 

 the plateau above the pits, hiding the junction of the old Tertiary 

 beds and the Chalk, and it is supposed to be of Glacial age, because 

 it is like other gravels near which run under the boulder-clay; for 

 such detached masses of gravel were presumed to be of the same 

 age as the larger masses of which they seemed to be outliers. 



After a pleasant walk across the fields the party arrived at the 

 "Woodcock Hill Kiln. Here the section exposed was found to be 



