1820.] Geological Society. 211 



land. Other pebbles that are mixed with them in the same 

 strata are probably derivative from the rocks of Charnwood 

 Forest. The destructibihty of this rock, in consequence of its 

 shattered and minutely divided state, aifords a reason why those 

 few portions of it which we find in the Lickey and at Caer 

 Caradoc and the Wrekin, are almost the only remaining frag- 

 ments of a formation which the abundance of its wreck proves 

 to have occupied a very considerable space before the deposilion 

 of the strata composing the young red sandstone formation. 

 Several places are specihed in the neighbourhood of Bridgnorth 

 and Kidderminster where these siliceous pebbles may be seen 

 forming part of, and imbedded in, the regular strata of the young 

 red sandstone formation. 



In the same neighbourhood, and indeed universally over the 

 central plains of England, the same pebbles occur mixed with 

 other pebbles of almost eveiy kind of English rock from granite 

 up to chalk, in the form of superficial gravel torn by the last 

 diluvian waters that have affected the earth from every substance 

 that lay within the influence of their currents, and drifted toge- 

 ther without any reference to the age or condition of the subja- 

 cent strata on which they are now accumulated. 



The extent of this gravel is not limited to the central plains ; 

 it has been drifted on within the area of the oolite formation by 

 two depressions or low hps in the high escarpment of the Cots- 

 wold hills, and has passed down the Even-lcde and Charwell 

 towards Oxford. 



The table-lands on each side the valley of Even-lode are 

 scattered over with those pebbles, and on the highest summit of 

 Witchwood Forest, Wytham Hill, and Bagley Wood, on the 

 north-west of Oxford, thick lips of gravel composed of these 

 pebbles from Warwickshire, arc accumulated on the surface of 

 strata belonoino- to the oolite formation. 



The position of these summits is exactly opposite the point 

 where tlie valley of the Even-lode falls into that of the Thames, 

 and where the diluvian currents descending the farmer valley 

 would evacuate their driftings. 



Similar pebbles occur in the gravel of the summit of Henley 

 Hill and in the gravel beds of the valley of the Thames, from 

 Oxford downwards to Hyde Park. 



But above that point where the driftings of Even-lode Gorge, 

 fall into the valley of the Thame.s, no such deposits of siliceous 

 pebbles are to be found along the course of the Salter river from 

 its head springs on the south side of the Cotsuold llillri. There, 

 is a considerable proportion of chalk Hints mixed up with the 

 gravel we arc considering; and the fact of its containing {)ebbles 

 of hard white chalk and of red chalk, such as occurs in no part 

 of the chalk of the south-east of England, but is common in the 

 lower strata of this formation, in Lincolnshire and Yorkshire, 

 goes far to show that these red pebbles and chalk iliuta have 



