188 NEOZOIC TIME. [CHAP. X. 



The first result of the great subsidence was the sub- 

 mergence of the promontory which existed on the site of 

 our eastern counties, and the outspread of the Gault muds 

 over the whole of south-eastern England ; at the same 

 time the western shore of the Cretaceous sea was carried 

 back to Devonshire, and doubtless also to the borders of 

 Wales, though subsequent detrition has destroyed all 

 evidence of the shore-line north of Devon. From the 

 present disposition of the Cretaceous strata, however, we 

 can hardly avoid the conclusion that the whole of central 

 England was once more converted into a sea-bottom, 

 on which sandy and glauconitic deposits were laid down, 

 just as such deposits are now formed along the bor- 

 ders of our great oceans at a certain depth and distance 

 from shore. Such deposits everywhere underlie the Chalk, 

 but we cannot regard them all as of the same absolute age, 

 because they were formed in a sea which was continually 

 spreading further and further to the west and the north, 

 so that the conditions which prevailed in England at the 

 epoch of the Gault and Upper G-reensand did not reach 

 Ireland till the time of the Lower Chalk, and no true 

 chalk was formed in that area till the time of our Upper 

 Chalk. 



At the close of the English Greensand stage, when the 

 Warminster beds were being deposited, the whole of south- 

 eastern and central England was covered by a shallow 

 sea, nowhere apparently more than 100 or 150 fathoms 

 deep, and gradually shallowing westward. In the south- 

 west it stretched to the borders of Dartmoor, and it washed 

 the foot of the North Devon and Quantock Hills ; the 

 valley of the Bristol Channel was a deep inlet, and thence 

 the shore-line swept northward below the hills of Glamor- 

 gan, Monmouth, and Hereford. The height attained by 

 the Greensand in the Blackdown Hills is not more than 

 600 feet, and these are on the same line of longitude as the 



