306 Dr Ch. Martins on the Marks of Glacial Action 



1400 feet beneath its present level, we have moreover to 

 admit a climate so extremely cold that, even in summer, the 

 temperature of the sea never rose above 32° Fahr., we impli- 

 citly admit an amount of cold much more intense than that 

 which suffices for the explanation by the presence of ancient 

 glaciers for the phenomena in the neighbourhood of Edin- 

 burgh. 



But these objections against the theory of floating icebergs 

 are not the only ones. When one of these enormous frag- 

 ments is separated, and falls into the ocean, it plunges deep, 

 rotates upon itself, reappears upon the surface of the waters, 

 swings and oscillates many times, till it attains a position of 

 equilibrium, which again is dependant upon that of its centre 

 of gravity. Seven-eighths of the floating mass are submerged, 

 one-eighth swims above. Hence, it rarely happens that the 

 inferior surface remains beneath ; and often, in reality it is 

 turned upwards, or upon its sides. Under these circum- 

 stances it can neither wear nor striate the rocks over which 

 it passes, for ice has not the power to polish the harder 

 rocks, such as traps and granites. Hence we perceive, that 

 a very small number of floating icebergs are in the necessary 

 conditions to striate the rocks, — namely, having their in- 

 ferior surface turned downwards, and containing imbedded 

 pebbles. In connection with this, it is not to be forgotten 

 that the roches moutonnee or rounded eminences so common in 

 the environs of Edniburgh, cannot have been produced by 

 casual icebergs. 



We have hitherto all along supposed, with the partizans 

 of the theory we are combating, that a floating iceberg 

 sweeping along with a current, had the power to wear, to 

 polish, and to striate a rock in situ. Nevertheless, we find 

 it impossible to conceal our doubts, and not to express our 

 incredulity in this matter. The existing glaciers produce 

 these effects under our eyes, because they act upon the under- 

 lying rocks like a colossal pressing-machine. Confined by 

 the flanks of a valley they descend slowly, and very much in 

 the same direction: their prodigious weight, varying from 

 that of 200 to 1200 feet of ice, presses upon the rock, and 



