574 



EEPEODUCTIVE EFFECTS OF CUKBENTS. 



[Ch. XXII. 



to subside one inch ;* while oxalate and phosphate of lime 

 require nearly an hour to subside about an inch and a half 



and two inches respectively^ so exceedingly small are the 

 particles of which these substances consist. 



When we recollect that the depth of the ocean is supposed 

 frequently to exceed three miles, and that currents run 

 through different parts of that ocean at the rate of four 

 miles an hour, and when at the same time we consider that 

 some fine mud carried away from the mouths of rivers and 

 from sea-beaches, where there is a heavy surf, as well as the 

 impalpable powder showered down by volcanos, may subside 

 at the rate of only an inch per hour, we shall be prepared to 



sediment 



indefinite extent. 



uncommon 

 :e more the 



Suppose 



mud 



feet per hour, and these to be discharged into that part of 



earn 



mean 



the Gulf-st 



miles an hour for a distance of two thousand miles ; in 

 twenty-eight days these particles will be carried 2,016 miles, 

 a.nrl will have fallen onlv to a denth of 224 fathoms. 



exam 



retains its superficial velocity at the depth of 224 fathoms, 

 for which we have as yet no data, although we have seen 

 that the motion of a current may continue at the depth of 

 100 fathoms. (See above, p. 498.) Experiments should be 

 made to ascertain the rate of currents at considerable dis- 

 tances from the surface, and the time taken by the finest 

 sediment to settle in sea-water of a given depth, and then 

 the geologist may determine the area over which homoge- 





mixtures may 



seas. 



* On the authority of Mr. Faraday. f On the authority of Mr. E. Phillips 













. 



r< 



- 







hi 



as : 









^ 







\ 







a; 





>*U 











;... 





