192 NEOZOIC TIME. [CHAP. X. 



though a thickness of over 400 feet of chalk was accu- 

 mulated in the south and east of England during this 

 time, it is probable that these were the areas of greatest 

 depression, and that the western and northern portions of 

 the British region did not sink to the same vertical extent. 

 We cannot judge of the levels reached by the Cretaceous 

 sea from the present relative levels of the Cretaceous strata 

 in Antrim and Mull, because these areas have undergone 

 an extensive local depression in Tertiary times, after the 

 outpouring of the great lava-streams under which the 

 Mesozoic strata are buried. We may be sure that in Pre- 

 Tertiary times the relative level of these districts was many 

 hundred feet higher than that at which they now lie, while 

 the height attained by the base of the G-reensand in Morvern 

 (Argyleshire) shows that the Cretaceous sea must have 

 covered considerable areas in western Scotland, and makes 

 it probable that all the lowland district was submerged so 

 as to form a strait or channel between the Highlands and 

 the southern uplands. The latter, with the Cheviot Hills 

 and the higher parts of Cumberland, Westmoreland, and 

 Yorkshire, must have formed a group of islands ; and it is 

 not unlikely that Ireland presented a similar appearance, 

 glauconitic deposits like those of Antrim being deposited 

 in the comparatively shallow waters between the islands 

 of the Irish archipelago. On this point we shall never 

 obtain definite information, but the very existence of such 

 deposits in Ireland and of chalk over so large a part of 

 England, makes it certain that no large areas of land then 

 existed, that the Cretaceous sea became more and more 

 oceanic, and that the British region had never been so 

 deeply submerged since the commencement of Neozoic 

 time. 



The subsidence had, however, by no means attained its 

 maximum extent, for at the epoch of the Chalk Rock the 

 downward movement seems to have been arrested ; and if 



