ALLUVIUM. RECENT FORMATIONS. 



783 



Jorullo in Mexico, at a single bound, starts up from a level plain to the height of 1600 feet 

 above the adjoining surface. 



To the preceding causes of geological change at present in action the agency of man 

 must be added, who, during the brief period of the existence of his race, has contributed 

 variously to modify his habitation, both involuntarily and by design. The human 

 population finally mingle their remains with the superficial formations, while large 

 draughts are continually made upon the strata to subserve the purposes of life, the 

 material of our cities, temples, dwellings, and bridges, with the metallic products and 

 carbonaceous matter in daily use, having been abstracted from the bowels of the earth. 

 In many localities man has reclaimed land from the dominion of the ocean by artificial 

 embankments, and now sows his corn where there was a periodical inroad of the tidal 

 waters ; and the degradation or elevation of the surface transpire in the prosecution of 

 his industrial designs. But it is especially upon the occupation of a new country by the 

 human race that a cycle of change commences in its physical character, which becomes 

 most marked upon an extensive multiplication of the species. Forests are cleared away, 

 producing a permanent effect upon the climate ; swamps are drained, and become pasture 

 ground ; the wild animals are supplanted by the domestic varieties ; and the introduction 

 of a new flora ensues, consisting of the leguminous plants and cereal grasses that 

 accompany man in his migrations. How different Britain at present from the island 

 upon which Ccesar landed, when extensive forests and vast morasses occupied the chief 

 part of its area, and the bear, the wolf, and the beaver were its tenants ; and within a 

 far more limited period, a precisely parallel alteration has transpired across the Atlantic, 

 as the effect of colonisation by the civilised races. 



Descent of the Curral, Madeira. 



