in.] THE STONES IN THE WALL. 81 



slightly different means, on which a whole chapter of 

 natural philosophy say, rather, natural theology 

 will have to be written some day. 



But now consider what this Lias, and the Oolites 

 and clays upon it mean. They mean that the New 

 Bed sandstone, after it had been dry land, or all but 

 dry land (as is proved by the footprints of animals 

 and the deposits of salt), was sunk again beneath the 

 sea. Each deposit of limestone signifies a long period 

 of time, during which that sea was pure enough to 

 allow reefs of coral to grow, and shells to propagate, 

 at the bottom. Each great band of clay signifies, a 

 long period, during which fine mud was brought down 

 from some wasting land in the neighbourhood. And 

 that land was not far distant is proved by the bones 

 of the Pterodactyle, of Crocodiles, and of Marsupials ; 

 by the fact that the shells are of shallow-water or 

 shore species ; by the presence, mixed with them, of 

 fragments of wood, impressions of plants, and even 

 wing-shells of beetles ; and lastly, if further proof was 

 needed, by the fact that in the " dirt-bed " of the 

 Isle of Portland and the neighbouring shores, stumps 

 of trees allied to the modern sago-palms are found as 

 they grew in the soil, which, with them, has been 

 covered up in layers of freshwater shale and lime- 

 stone. A tropic forest has plainly sunk beneath a 

 lagoon ; and that lagoon, again, beneath the sea. 



And how long did this period of slow sinking go on ? 

 Who can tell ? The thickness of the Lias and Oolites 

 together cannot be less than a thousand feet. Con- 

 sidering, then, the length of time required to lay down 

 a thousand feet of strata, and considering the vast 

 difference between the animals found in them, and the 

 so. G 



