592 



A. W. GRABAU TYPES OF SEDIMENTARY OVERLAP 



ing correspondence in the lithic character of the sections when read from 

 the base upward; but this correspondence is not parallel in synchronous 

 formations, for the base of the Irish Cretacic is much higher than that of 

 the English. The following sections will illustrate this point : 



Figure 3. — Diagrammatic Comparison of Irish and English Cretacic. 



In England the basal formation is the lower Greensand (Aptian), 

 which rests on the non-marine Wealden, and is a glauconite and clay 

 formation with basal conglomerates. The corresponding lithic bed in 

 Antrim county, Ireland, is the Cenomanian, which rests on Lias and 

 Ehaetic. The distance is from 300 to 400 miles, in which interval the 

 lower Greensand and Gault have disappeared by overlap, bringing the 

 Cenomanian directly on the old land surface. During the advance, how- 

 ever, the deepening of the English area, and above all the removal of the 

 coast, permitted the deposition of chalk in that region, so that the 

 Cenomanian of England is a chalk, though it still contains Greensand 

 and marl. It is the Lower Chalk of the British geologists. The corre- 

 sponding lithic bed of Ireland — that is, the Lower Chalk of Ireland, 

 lithically considered — is lower Senonian. Between this and the basal 

 Lower Greensand (Cenomanian of Ireland, Aptian of England) is a 

 glauconitic sand, clay, and marl formation, which in England is the Gault 

 or Upper Greensand (Albian), while in Ireland it is the Turonian, and 



