28 MR. G. M. DAVIES ON THE [vol. lxXV,. 



calcareous fossils, the phosphatic fish-remains and concretions^ 

 and the manganese oxide. Later, the calcareous and phosphatic 

 materials were removed in solution, and also the manganese, but 

 the latter was precipitated by the bicarbonate of lime in the 

 water near the chalk walls of the pipes. Thus the gre} r clay was. 

 enriched in manganese at the expense of the red clay. 



As the pipes continued to increase in depth and area, the Clay- 

 with-Flints was let down, still in contact with the Chalk surface,, 

 while the sand and pebbles filled the central portions of the pipes. 

 This downward movement gave rise to the banding and vertical 

 grooving sometimes seen in the clay, and also to the abundant 

 splinters of flint. 



We see at Worms Heath the transition from rotten Chalk con- 

 taining fossils, through grey Clay- with- Flints containing the same 

 fossils, to the common red Clay-with-Flints from which almost 

 everything soluble has disappeared. There can in this case be no- 

 doubt as to the residual character of the Clay-with-Flints, and it 

 is unfortunate that the term cannoc be restricted to such deposits 

 as are formed in situ by the solution of the Chalk. That was 

 Mr. Whitaker's definition when he introduced the name. A large 

 proportion of the deposits mapped as Clay-with-Flints in Surrey, 

 however, indicate a considerable amount of transport and ad- 

 mixture with Tertiary pebbles and cla}^, Lower Greensand chert 

 and ironstone, etc. The origin of such deposits is not elucidated 

 by the sections at Worms Heath. 



Discussion. 



Mr. Gr. Barrow said that he was interested in the mode of 

 occurrence of the masses of well-rounded flint-pebbles in the Lower 

 London Tertiary Beds. The smallest that he had seen filled 

 channels only some 2 feet broad by 2 feet in depth, yet the stones 

 were of fair size. The difficulty is to know what force drove them 

 along these channels and whence they came, as there is no known 

 source within miles of their present position. From these we have 

 a gradation to masses fully half a mile across, such as that on the 

 Scullet Hill, near Chorley Wood, in Hertfordshire ; in this no 

 material other than rounded flints with a black exterior has yet 

 been found. The evidence on the north side of the Thames seemed 

 to suggest that the cutting of these channels began at a certain stage 

 in the Reading Beds ; but some of the channels were cut deeper 

 and lasted longer than others. It had occurred to the speaker that 

 the Blackheath pebbles may lill an exceptionally large and deep 

 channel of much the same nature, and possibly started somewhat 

 later. The curious disc-like pebbles of quartzite (such as that 

 exhibited) which so far seemed restricted to the Blackheath Beds 

 were interesting, as the speaker believed them to be composed of 

 sarsen, and they certainly seemed identical with the sarsens ]3roved 

 to be in situ in the Reading Beds. Thus a large sarsen was cut 

 across in making the railway at Gerrard's Cross ; another was met 



