304 EOCENE PERIOD. 



[Ch. XXII. 



been invariably brought back again to the opinion, that the 

 chalk was originally continuous, on a more deliberate review of 

 the whole phenomena. 



It may be useful to consider the only other alternative of the 

 hypothesis before explained. If the marine groups, Nos. 1, 

 2, 3, were not originally continuous, it is necessary to imagine 



No. 77. 



1, Chalk and Upper grcen-sand.| 4j Weal(1 c] .^ 



2, Gault. > Marine. ^Fresh-water. 



3, Lower green-sand. J 5 ; Hastings sands._ 



that they each terminated at some point between their present 

 outgoings and the secondary strata of the Forest ridge. Thus 

 we might suppose them to have thinned out one after the other, 

 as in the above diagram, and never to have covered the entire 

 area occupied by the fresh-water strata, Nos. 4 and 5. 



We grant that had such been the original disposition of the 

 different groups, they might, as they gradually emerged from 

 the sea, have become denuded in the manner explained in the 

 last chapter, so that the country might equally have assumed its 

 present configuration. But, although we know of no invincible 

 objection to such an hypothesis, there are certainly no appear- 

 ances which favour it. If the strata Nos. 4 and 5 had been 

 unconformable to the Lower green-sand No. 3, then, indeed, we 

 might have imagined that the older groups had been disturbed 

 by a series of movements antecedently to the deposition of 

 No. 3, and, in that case, some parts of them might be supposed 

 to have emerged or formed shoals in the ancient sea, interrupt- 

 ing the continuity of the newer marine deposits. But the group 

 No. 4 is conformable to No. 3, and the only change which has 

 been observed to take place at the junction, is an occasional in- 

 termixture of the Weald clay with the superior marine sand, 

 such as might have been caused by a slight superficial move- 

 ment in the waters when the sea first overflowed the fresh- 

 water strata. 



