BEFORE AND AFTER 79 



ice sheet in Greenland, or other arctic country. No 

 doubt the winters must have been very severe, hard 

 frosts and heavy snows, the ground frozen deep. Some 

 arctic animals would manage to live as they do now just 

 outside the ice sheet in Greenland. Now, have we any 

 deposits formed at that time in the Isle of Wight ? I 

 think we have. A large part of the surface of the Island 

 is covered by sheets of flint gravel. The gravels differ 

 in age and mode of formation. We have already con- 

 sidered the angular gravels of the Chalk downs, com- 

 posed of flints which have accumulated as the chalk which 

 once contained them was dissolved away. But there are 

 other gravel beds, which consist of flints which, after they 

 were set free by the dissolution of the chalk, have been 

 carried down to a lower level by rivers or other agency, 

 and more or less rounded in the process. Many of these 

 beds occur at a high level ; and, as they usually cap flat- 

 topped hills, they are known as Plateau Gravels. Per- 

 haps the most remarkable is the immense sheet of gravel 

 which covers the flat top of St. George's Down between 

 Arreton and Newport. Gravel pits show upwards of 

 30 feet of gravel, consisting of flints with some chert and 

 ironstone, and the greatest thickness is probably con- 

 siderably more than this. The southern edge of the 

 sheet is cut off straight like a wall. To the north it runs 

 out on ridges between combes which have cut into it. In 

 places in the mass of flints occur beds of sand, which have 

 all the appearance of having been laid down by currents 

 of water. The base of the gravel where it is seen on the 

 steep southern slope of the down has been cemented by 

 water containing iron into a solid conglomerate rock. 

 The flints forming this gravel have not simply sunk down 

 from chalk strata dissolved away ; for they lie on the 

 upturned edges of strata from Lower Greensand to Upper 

 Chalk, which have been planed off, and worn into a 

 surface sloping gently to the north ; and over this surface 



