138 Physical Geography. 



Mississippi has an area of more than 12,000 square 

 miles, consisting chiefly of sands and clays, with much 

 vegetable matter, and that of the Nile an area of about 

 21,000. The delta of the Ganges and Brahmapootra is 

 more than 48,000 square miles in extent, has peaty 

 beds interstratified with clays and sands, containing 

 freshwater shells and freshwater tortoises, often much 

 below the level of the neighbouring sea. The area of 

 all England and Wales is 57,812 square miles, and 

 the areas of all the coal-fields of Great Britain extended 

 to their original size did not equal that of this great 

 delta. 



It is not to be supposed that, in each coal* field, each 

 bed of coal extends over the whole area. On the con- 

 trary they thicken and thin out, and have their edges 

 like many a modern peat moss, and the vegetation of 

 the Carboniferous epoch flourished and decayed rapidly, 

 on moist ground and in a moist atmosphere, not of 

 excessive warmth, as has often been stated, but, in the 

 opinion of Sir Joseph Hooker, ' in a moist and equable 

 climate,' that could scarcely have been sub-tropical. 



