CHAP. X.] CRETACEOUS PERIOD. 193 



the inferences drawn from the facts previously recorded 

 (p. 177) are correct, there was actually an uplift raising 

 the sea-floor in England till the water above it was not 

 more than 100 or 150 fathoms deep. There is no clear 

 evidence of any such oscillation in the Irish succession, 

 but the white sandstones of Morvern (see p. 177) do lend 

 some support to the view that the formation of the Upper 

 Chalk was preceded by a movement of elevation, so that 

 beds of estuarine origin, with the remains of something 

 like a terrestrial surface, are here intercalated between 

 marine deposits. 



The subsequent subsidence must have been more rapid 

 and still more extensive than that which had previously 

 taken place, but we still find deposition prevailing more 

 in the east than the west, and it was not until 250 feet 

 of chalk had been accumulated over the Chalk Rock in the 

 east of England that true chalk began to be formed in 

 Ireland, and even then it was deposited so slowly that only 

 90 feet seem to have been accumulated in the time that 

 600 or 700 feet were formed in England ; we may, there- 

 fore, conclude that the western region was never so deeply 

 submerged as the eastern. 



During the formation of this chalk it would seem that 

 little of England or Wales could have remained above the 

 level of the sea, for we must remember that such chalk i& 

 a deep-sea deposit, and is not now formed in water of less- 

 than 400 or 500 fathoms. If we suppose that at the epoch 

 of the Chalk Marl central Wales was already so submerged 

 that the sea-level stood at the 1,000 feet contour, that 

 during the subsequent subsidence 500 feet of chalk were 

 deposited around it, and that the highest bed of this chalk 

 had 400 fathoms (2,400 feet) of water over it, it is clear 

 that all the present surface of Wales would be under 

 water ; and even if we allow for subsequent detrition by 

 supposing that from 800 to 1,000 feet of rock has been 



o 



