POLAR ICE-CAPS AND SEA LEVELS. 343 



Here is another model, which was only started 

 to-day, placed in water so that the board is just at 

 the water level. You see we have the continental 

 features complete with a long slope down to the sea 

 on one side, a deep gorge, a precipice, and yet 

 another slope down into the sea ; and these varia- 

 tions of boundary are sufficient to show the 

 various effects due to the shape of the land under 

 a plastic body : everywhere ice flowing seawards 

 breaking off when sea-borne, and making ice-bergs. 

 That shoemaker's wax is a substance which we 

 know and see to be plastic ; here is a substance 

 ice which we might not know to be plastic, but 

 which Forbes proved to move as a plastic body in 

 the Swiss glaciers. My brother's theory of the 

 plasticity of ice, in virtue of melting by pressure 

 and regelation, is admirably illustrated by an ex- 

 periment of Mr. J. T. Bottomley. Here is a mass 

 of clear ice having a piece of copper wire hung 

 upon it, with a weight attached of 56 Ibs. This 

 wire will not go through the ice in less than an 

 hour, but we see it already sinking into the ice at 

 the corners it is about half an inch in, and if we 



