1856.] 



BABBAGE — OCEAN-CURRENTS. 



367 



are shown in the following table, in which four varieties of sediment, 

 falling respectively through 10, 8, 5, and 4 feet of water per hour, 

 are laid down: — 



No. 



Velocity of 

 fall per hour. 



Nearest di- 

 stance of de- 

 posit to river. 



Length of 

 deposit. 



Greatest di- 

 stance of de- 

 posit from 

 river. 



1. 

 2. 

 3. 



4. 



Feet. 

 10 



8 



5 



4 



Miles . 

 180 



225 



360 



450 



Miles. 

 20 



25 



40 



50 



Miles. 

 200 



250 



400 



500 



Thus four separate deposits will be found at various distances from 

 their common origin. 



The author noticed also how the uniformity of a stratum might be 

 interfered with by the varying conditions both of the sediment and 

 of the sea-bottom. Altered relations between the specific gravity, 

 the shape, and the size of the particles, when duly adjusted, render 

 ocean-currents capable of either separating mixed substances, or of 

 combining together diiferent substances. Hence endless combina- 

 tions arising from the variation of these conditions. 



Local elevations and depressions of the sea-bed, on which sediment 

 brought from a distance is deposited, were pointed out as probable 

 causes of irregularities in stratified deposits, — giving origin, indeed, 

 to outliers or disconnected masses, which might be sometimes sup- 

 posed to have been due to subsequent denudation. 



Sedimentary matter carried by ocean-currents to the profound 

 depths of the ocean subside into these depths beyond the reach both 

 of currents and of wave-action. The downward motion becomes 

 continually diminished, and the particles ultimately come to absolute 

 rest, or move through water of increasing density with excessive slow- 

 ness, so as to cover the ocean-bottom with an incoherent pulpy mass 

 of fluid mud, of great thickness, and less dense for the most part in 

 the upper than in the lower part, — or to form a similar mass of sedi- 

 ment suspended in mid- water. 



It was also pointed out that in the immense period of time during 

 which this sediment is subsiding into the profound ocean- depths and 

 massing itself into a mud-bed, various hydrographical changes might 

 take place and cause new currents to bring diiferent sediments over 

 the same area, which newer deposits might descend into and be 

 mingled with the older precipitates. 



The author proceeded to treat of the effects of an alteration of 

 isothermal surfaces, caused by the interference of this more or less 

 suspended mud- cloud with the conduction of heat from the earth's 

 surface. Consolidation of the lower strata would be caused by the 

 isothermal surfaces below the ocean rising upwards. Currents of 

 heated water, similarly caused, might variously disturb the sediment 

 and give it flexuous stratification. Heated water might be retained 



