THE BAGSH0T BEDS OF THE LONDON BASIN. 385 



tained the same thickness here as in the well-section. They must 

 therefore have thinned away considerably. 



Again, a comparison of altitudes gives the following data : — 



Altitudes at W. Coll. 



Altitudes at outcrop. 



Distance. 



Rise. 



Ratio. 



No. 3 264 



264 



4380 ft. 



0* 





Base of No. 10 ... 187 



214 



5544 ft. 



27 ft, 



1 in 205 



Surface of L. Clay 92 



200 



3460 yds. 



36 yds. 



1 in 96 



By ordinary rules of stratigraphy (rejecting the notion of east and 

 west flexures), no. 3, if continued, would cut through the Easthamp- 

 stead and Bracknell Hills at about the altitude at which a pebble- 

 bed is found there ; a rise to the north of 1 in 205 for base of no. 10 

 would give 272 (O.D.) along the same line of country (see fig. 2), which 

 with further subsidence to the south gives a lithologically equivalent 

 bed at Eracknell and Buckhurst, in each case underlain by a fine 

 quartz-sand (see infra, p. 387), while intermediate outliers of it 

 at intermediate levels are met with on the north side of Easthanrpsteatl 

 Park ; and a rise of 1 in 96 for the surface of the London Clay gives 

 274 (O.D.) along the same line of country, the difference between 

 this and the general altitude of that formation beneath the Eagshot 

 beds along that line of country representing probably the amount of 

 contemporaneous denudation of the London Clay. Seasoning from 

 these data, we should expect to find that the green-earth series 

 and the quartz-sand series were represented very feebly, if at all, 

 at Buckhurst and Bracknell ; and so the difficulty arising from the 

 non-appearance of the green earths in the Bracknell cutting (Quart. 

 Journ. Geol. Soc. vol. xlii. p. 406) vanishes. 



Elevation of the Beds N. W. from the Well-section. 



When this paper was read a diagram showing a continuity of levels 

 in beds nos. 3 to 7 to the ~N.W. from the College- well was shown f . 

 It was constructed by correlating, according to altitudes, minor 

 sections at the railway-cutting, in the new well behind the Hotel, 

 in the pine-woods near Heath Pool, and in the lane below Wick 

 Hill Earm (Upper Eagshot), taking the intermediate features of the 

 ground into account. A detailed section (constructed from exca- 

 vations made for me last autumn, the measurement of the beds 

 in the fresh section, and a correlation by measurement of the levels 

 of the beds in the two subsections, one in the old clay-pit, the other 

 in the California brick-yard) was also shown and described. Here 

 it will suffice to state, as the outcome of the investigation, that (1) 



* Further investigation has shown that this level is maintained for about 

 half a mile south of the College. 



t Cf. Whitaker, Quart. Journ. Geol. Soc. vol. xviii. p. 263. 



