112 PEOCEEDINQS OF THE GEOLOGICAL SOCIETY. [Jan. 23, 



longer and broader tlian they are thick : one or two that I measured 

 were six feet in length, containing from 80 to 90 cubic feet of stone, 

 and must have weighed from four to five tons ; others (which had 

 been broken up) appeared to have been of much larger dimensions. 

 The whole of the blocks showed a distinct bedding, which when in 

 situ invariably ranged with the stratification of the drift ; and I was 

 therefore convinced that the consolidation had taken place where they 

 occurred. One remarkable point was the isolation of each individual 

 block ; for although the masses were placed at a general level, they 

 did not appear to occur as a connected band. There was not even 

 any gradation between the extreme compactness and hardness of the 

 blocks and the loose drift forming a horizontal continuation of their 

 strata, and out of which they were evidently composed. 



The power of consolidation did not seem to be related to any 

 particular variety of the drift, as some of the blocks were composed 

 wholly of sand, some entirely of pebble-beds and gravel, and a few 

 of the thicker individuals included alternations of fine sands and 

 pebble-beds in the same block, all alike remarkable for their extreme 

 hardness. 



The general aspect of the blocks, although varying much in 

 character and composition, strongly resembled the " Greywethers " 

 or "Druid Sandstones" of Wilts and Berks. Some were quite sac- 

 charoid in structure; and others could not be distinguished from 

 compact miUstone-grit, except by the presence of fragments of flint ; 

 indeed, hand- specimens might be selected to match almost any of the 

 sandstones and conglomerates of the Palaeozoic rocks, which they 

 more closely resemble than later formations. A'few of the blocks con- 

 tained comminuted chalk; and as these were invariably softer than the 

 others, it occurred to me that they might be in a more incipient 

 stage of concretion than the saccharoid blocks, which exhibit no 

 trace of separate chalk particles. It is possible that the finely divided 

 chalk first formed the cementing medium, and that on its gradual 

 dissolution the crystalline structure of the blocks has been slowly 

 perfected through the agency of a small quantity of lime in solution. 

 Some of the blocks are so extremely compact that the original sandy 

 agglomeration seems to have given way to an inherent crystalline 

 structure. The water of the well sunk through the drift is strongly 

 chalybeate, and throws down, on standing, a thick sediment of lime 

 and iron ; the drift-bed itself, therefore, supplies all the conditions 

 necessary for its consolidation. 



On reaching the sand through the Boulder-clay in sinking the 

 well, much " foul air " or carbonic-acid gas was given oif ; and from 

 this cause the life of one of the well-sinkers was sacrificed. The 

 discharge of gas, apparently from the chalk, still continues ; and it 

 may be distinctly heard bubbhng up through the water, which stands 

 at a level with the top of the chalk. The solvent power on lime and 

 iron, of carbonic acid in solution, will readily account for the chaly- 

 beate character of the water, and suggests an explanation of the 

 means by which the drift was first cemented together : the commi- 

 nuted chalk, which is largely intermixed with the sand and gravel, 



