WANSTEAI) AND WALTHAMSTOW, ESSKX. II9 



and near South Ockenden, and in gravels south of the Thames at 

 Tilehurst near Reading, on the hills above Bisham and Cookham, 

 and on Dartford Heath. 



The second is a fragment of a large pebble which was found by 

 Mr. James Baker during the excursion of the Geologists' Association 

 to Walthamstow on May yth, 1892. It was in the gravel of the cut- 

 ting on the railway at Stoneydown. On being broken up it was 

 found to be composed of a very hard brownish-red quartzite, with 

 scattered particles of a glistening mineral, probably mica, and to con- 

 tain a number of casts and impressions of a small Brachiopod shell, 

 Orihis hudleighensis (Dav.).'"' This shell is of Lower Silurian age. It 

 is said to fill whole beds at May and other places in Normandy and 

 to occur in Brittany. It has also been recorded from the quartzites 

 near Gorran Haven, in Cornwall. It has been found in pebbles in 

 the Triassic pebble bed of Budleigh Salterton on the south coast of 

 Devonshire. The origin of these pebbles is doubtful, and the ques- 

 tion has given rise to great discussion, but the best opinion seems to 

 be that they were to a large extent derived from Cambrian and 

 Silurian rocks which were destroyed during the formation of the 

 English Channel. 



Pebbles containing this shell have been found in the Bunter 

 Pebble Beds of Staffordshire, and are recorded from the Drift near 

 Birmingham, Warwick, Leicester, and Nottingham. Professor Bonney 

 showed me one which he found in Staffordshire — a whitish quartzite, 

 full of casts of the shell in question. The place from which these 

 pebbles were derived is uncertain, but there can, I think, be little 

 doubt that the Walthamstow pebble was derived from a northern 

 source.' 



Besides these pebbles of pink quartzite and brownish-red quartzite 

 with fossils, which very probably are derived from the Bunter con- 

 glomerate, many of the other quartzite and quartz pebbles found 

 in the Thames Gravels have probably come from the same source. 

 As to the sandstone pebbles, it was suggested by Mr. J. W. Davis 

 that they may very likely be Coal Measure sandstone. 



The Lower Greensand chert, I believe, came originally from the 

 south. The proportion varies a good deal in the different gravels. 



6 See the report of the excursion by J. \V. Gregory, F.G.S., Pros. Geol. Assoc, 1832, vol. xii., 

 p. 338 ; and also Essex Nat., vol. vi., p. g7. 



7 My authorities for the above are Davidson's "Brit. Foss. Brachiopoda," vol. iv., p. 317 ; 

 Bonney, "Geol. Mag.," 1880, vol. vii., p. 404 ; H. B. Woodward, "Geol. of Eng. and Wales," 

 2nd edit., 1887, pp. 75, 225, etc. 



