CHAP. I.] DRIFTING OF ICEBERGS. 17 



100 fathoms deep, the average depth over the Great Bank being 

 from forty to fifty fathoms. That they should be arrested in. 

 their course is not; surprising, when we consider that the mass of 

 floating ice below water is eight times greater than that above ; 

 and Sir James Ross saw icebergs which had rur. aground in 

 Baffin s Bay, in water 1500 feet deep. If we reflect on the 

 weight of these enormous masses, and the momentum which 

 they accjuire when impelled by winds and currents, and when 

 they are moving at the rate of several miles an hour, it seems 

 difficult to over-estimate the disturbance which they must create 

 on a soft bottom of mud or loose sand, or the grinding power they 

 must exert when they grate along a shelf of solid rock overspread 

 with a layer of sand. 



Mr. Redfield of New York has lately published * a chart show 

 ing the positions of the icebergs observed in the North Atlantic 

 daring the last fifteen years, and it will be remarked, that they 

 have been met with at various points between the 47th and 36th 

 parallels of latitude, the most southern being that which Captain 

 Couthuoy encountered, lat. 36 10 N., long. 39 W., a mile 

 long and 100 feet high. This berg w^as on the extreme southern 

 boundary of the gulf stream, which it had crossed against the 

 direction of the superficial current, so as to get as far south as the 

 latitude of the Straits of Gibraltar. In fact, these great ice- 

 islands coming from the Greenland seas are not stopped by the 

 gulf-stream, which is a mere superficial current of warmer water 

 flowing in an opposite direction, but are borne along from N.E. 

 to S.W. by the force of the arctic under-current, consisting of 

 colder water, into which the icebergs descend to a great depth. 



All the circumstances connected with the geographical outline 

 of the coast, the shape of the sea-bottom, the oceanic currents, 

 and the prevailing winds, although liable to be modified and 

 greatly altered in the course of time, may continue nearly the 

 same for the next ten thousand or twenty thousand years ; and 

 in that period thousands of bergs, occasionally charged with frag 

 ments of rock, and many of them running aground in a variety 

 of places, will be conveyed in every century over certain tracts 

 * Amer. Journ. Science, vol. xlviii. 1844, 



