English Formations. 311 



fig. 72, p. 339, marked w, h, proving that they are 

 intermediate in date to the Oolites and Cretaceous rocks, 

 for in the Isle of Purbeck, near Swanage, they are seen 

 lying between the two (fig. 75, p. 348). 



This episode at last came to an end, by the complete 

 submergence of the Wealden area, and of the greater 

 part of England besides ; and upon these fresh-water 

 strata, and the Oolitic and other formations that partly 

 formed their margins, a set of marine sands and clays 

 were deposited in the south of England, consisting of 

 the Atherfield Clay and the Lower Grreensand s, d (fig. 

 72, p. 3M9) is now often classed with the Upper Neoco- 

 mian beds of the Continent, but in England they have 

 till lately generally been known as the Lower Cretaceous 

 strata. The distinction is not important to my present 

 purpose. Then comes the clay of the Grault, above 

 which lies the Upper Grreensand. Kesting upon the 

 Upper Grreensand comes the Chalk (No. 11, fig. 57, and 

 c. fig. 72), the upper portion of which contains numerous 

 bands of interstratified flints, which originally were 

 partly marine sponges, since silicified. The Chalk, 

 where thickest, is from one thousand to twelve hundred 

 feet in thickness. The Liassic and Oolitic formations 

 were sediments spread in warm seas surrounding an 

 archipelago of which Dartmoor, Wales, Cumberland, 

 and the Highlands of Scotland formed some of the 

 islands. But the Chalk was a deep sea deposit, formed 

 to a great extent of microscopic foraminiferse, and while 

 it was forming in the wide ocean, it seems probable that 

 the old islands of the Oolitic seas subsided so completely, 

 that it is doubtful whether or not even Wales and the 

 other older mountains of Britain were almost entirely 

 submerged. 



During the period that the Oolitic formations formed 



