Ch, XX.] TERTIARY OUTLIERS ON CHALK. 283 



Apennines, and Pyrenees, we find the newer formations reposing 

 unconformably upon the truncated edges of the older beds, and 

 it is clear that, in many cases, the latter had been subjected to 

 a complicated series of movements before the more modern 

 strata were formed. The latter rise only to a certain height 

 on the flanks of the mountains which usually tower above 

 them, and are recognized at once by the geologist as having 

 been upraised into land when the tertiary formations were still 

 forming in the sea. The ancient borders also of that sea can 

 often be defined with certainty, and the outline of some of its 

 bays and sea-cliffs traced. 



In England, although undoubtedly the greater portion of the 

 tertiary strata is confined to certain spaces, we find outlying 

 patches here and there at great distances beyond the general 

 limits, and at great heights upon the chalk which separates the 

 basins of London and Hampshire*. I have seen masses of 

 clay extending in this manner to near the edge of the western 

 escarpment of the chalk in Wiltshire, and Mr. Mantell has 

 pointed out the same to me in the South Downs. Near the 

 escarpment at Lewes, for example, there is a fissure in the 

 chalk filled with sand, and with a ferruginous breccia, such 

 as usually marks the lower members of the Plastic clay for- 

 mation. From the fact of these tertiary outliers Dr. Buckland 

 inferred, ' that the basins of London and Hants were origi- 

 nally united together in one continuous deposit across the now 

 intervening chalk of Salisbury Plain in Wilts, and the plains 

 of Andover and Basingstoke in Hants, and that the greater 

 integrity in which the tertiary strata are preserved within the 

 basins has resulted from the protection which their compara- 

 tively low position has afforded them from the ravages of dilu- 

 vial denudation f.' 



We agree so far with this conclusion as to believe that the 



basins of London and Hampshire were not separated until part 



of the tertiary strata were deposited, but we do not think it 



probable that the tertiary beds ever extended continuously over 



* Dr. Buckland, Geol. Trans., Second Series, vol. ii. p. 125. t Ibid., p. 126. 



