150 NEOZOIC TIME. [CHAP. IX. 



the original limits of the latter ; that on the sites of the 

 English and Bristol Channels there were gulfs which 

 narrowed westward, and that the Mendip Hills seem to 

 have formed an island, parts of which remained above the 

 level of the sea throughout the whole epoch, whence we 

 may conclude that the slopes of the hills were then very 

 steep, and that their higher parts rose to a height of 800 

 or 900 feet above the level of the Rhaetic waters. 



From Swansea Bay the coast probably ran through 

 Glamorgan and Monmouth to the Malvern Hills, and 

 thence trended north-westward through Shropshire and 

 Denbighshire, and across the Irish sea to the west coast of 

 Ireland. As to the space now occupied by the Irish 

 Channel no evidence is forthcoming, but if a gulf then 

 existed on its site, it probably opened northward, and 

 narrowed southward. From Ireland the sea extended over 

 the site of the western Scottish lake, and thence probably 

 up the great glen to the north-eastern basin ; here the 

 estuarine beds of the Lower Lias mark the debouchure of 

 a large river, but the overlying marine beds show that as 

 the submergence proceeded the sea gained on the land, 

 while the sandy beds of the Middle Liasr prove that the 

 narrow water spaces were soon silted up. 



With regard to the eastern limits of the Liassic sea we 

 know that it encroached considerably upon the eastern 

 land, for near Northampton, where the Trias is only from 

 50 to 100 feet thick, the Lias is over 700 feet, and this 

 thickness must carry it some 30 or 40 miles further east, 

 unless the slope of the eastern land became very steep. 

 Further south it probably thins out beneath the Chiltern 

 Hills (see fig. 3), and thence we may suppose that its 

 boundary curves round to the south-east below Berkshire, 

 Surrey, and Sussex, and crossing the English Channel 

 enters France a little to the north of Abbeville. 1 North - 



1 De Lapparent, " Trait4 de la Geologie," second edition, p. 912. 



