CHAP. X.] CRETACEOUS PEEIOD. 191 



not think that this range was submerged till the time of 

 the Middle or Upper Chalk. 



The remarkable change, however, which takes place in 

 the character of the Eed Chalk when followed along the 

 northern face of the Yorkshire Wolds, and its partially 

 argillaceous condition at Speeton (see p. 171), are facts 

 which suggest that currents carrying fine silt came from a 

 north-easterly direction, and that their influence was felt 

 as far south as the north-east of Yorkshire. This conside- 

 ration leads us to infer that continental land existed at 

 some distance north and north-east of the present outcrop 

 a land which doubtless included Scotland and Scandinavia, 

 and would effectually shut out the Arctic currents ; it is at 

 the same time quite possible that its highest mountains 

 were snow- clad, and they may even have nourished glaciers 

 which reached far down the valleys toward the shores of 

 the great European Ocean. 



There would at length come a time when the barriers 

 which limited the Greensand sea were breached and over- 

 topped, when Wales was nearly isolated, and the hills of 

 Devon and Cornwall converted into islands ; the sea then 

 spread to the north-west, over the areas of the older 

 Mesozoic rocks, to the north of Ireland and the west coast 

 of Scotland. The facts observed in connection with the 

 Chloritic Marl and Cambridge Greensand seem to tally 

 with what we might expect to be the results of such a 

 change. The currents would be altered, and it is probable 

 that strong currents would set either toward or out of the 

 straits between Wales and Derbyshire, and to the scour of 

 such currents the evidences of erosion at this epoch may 

 be due. 



It is very difficult to say how far west this subsidence 

 carried the Cretaceous sea, or to what extent Ireland and 

 the north of England were submerged during the formation 

 of the Lower and Middle Chalk in southern England ; for 



