LIFE ON THE EARTH. 125 



ceed the expectation of scientific navigators. The 

 fine sediments of the Maranon were still discoverable 

 by Sabine at the discoloured surface of the sea 300 

 miles from the mouth, so that in fact even the deep 

 central valleys and gulphs of the Atlantic may be 

 receiving sediments from the Western Chains of 

 America, mixed with, perhaps alternating with other 

 particles from the interior of Africa. The extent of 

 modern oceanic deposits may thus be admitted as equal 

 to that of the ancient Strata; if so, the Uniformitarian 

 calculation becomes of easy application. 



Take any large surface of the land, which yields 

 to the atmospheric agency unequally in different 

 parts, because granite, limestone, and sandstone, are 

 unequally acted on by rains, and frosts, and carbonic 

 acid; observe and measure what is carried away by 

 one or more rivers from this surface to the sea in 

 one year. Assume this to be a fair average for the 

 whole surface of the land, and, to save trouble, sup- 

 pose the whole of the sediment to be spread out on 

 the sea-bed, over an area equal to that from which 

 it was derived. The thickness wasted from the land, 

 in one year, is thus the same as that added to the 

 sea-bed in one year. Divide by this thickness the 

 measured thickness of the sedimentary strata, the 

 result is the number of Uniformitarian years em- 

 ployed in depositing the strata, if the materials were 



