308 James Croll — On the Glacial Epoch. 



miles at that place. It may be kere mentioned tkat had the section 

 been drawn upon a much larger scale — had it, for instance, been 

 made seven feet long, instead of seven inches — it would have shown 

 to the eye in a more striking manner the thinness of the cap. 



But to avoid all objections on the score of over-estimating the 

 thickness of the cap, I shall assume the angle of the upper surface 

 to be only a quarter of a degree, and the thickness of the sheet 

 one-half what it is represented in the section. The thickness at the 

 Pole will then be only six miles instead of twelve, and the mean 

 thickness of the cap two instead of four miles. 



Is there any well-grounded reason for concluding the above to 

 be an over-estimate of the actual thickness of the Antar-ctic ice ? 

 It is not so much in consequence of any a priori reason that can 

 be urged against the probability of such a thickness of ice, but 

 rather because it so far transcends our previous experience that we 

 are reluctant to admit such an estimate. If we never had any ex- 

 perience of ice thicker than what is to be found in England, we 

 should feel startled on learning for the first time that in the valleys 

 of Switzerland the ice lay from 200 to 300 feet in depth. Again, if 

 we had never heard of glaciers thicker than those of Switzei'land, 

 we could hardly credit the statement that in Greenland they are 

 actually from 2000 to 3000 feet thick. We, in this country, have 

 long been familiar with Greenland; but till very lately no one ever 

 entertained the idea that that continent was buried under one con- 

 tinuous mass of ice, with scarcely a mountain top rising above the 

 icy mantle. And had it not been that the geological phenomena of 

 the Glacial epoch have for so many years accustomed our minds 

 to such an extraordinary condition of things. Dr. Eink's description 

 of the Greenland ice would probably have been regarded as the ex- 

 travagant picture of a wild imaginatiom 



Let us now consider whether or not the facts of observation and 

 experience, so far as they go, bear out the conclusions to which 

 physical considerations lead us in reference to the magnitude of 

 continental ice ; and more especially as regards the ice of the 

 Antarctic regions. 



First. In so far as the Antarctic ice-sheet is concerned, observation 

 and experience to a great extent may be said to be a perfect blank. 

 One or two voyagers have seen the outer edge of the sheet at a few 

 places, and this is all. In fact, we judge of the present condition 

 of the interior of the Antarctic Continent in a great measure from 

 what we know of Greenland. But, again, our experience of Green- 

 land ice is almost wholly confined to the outskirts. No one, with 

 the exception of Dr. Hayes and Prof. Nordenskiold, has penetrated 

 to any distance into the interior. Dr. Hayes's excursion was made, 

 however, not upon the real inland ice, but upon a smaller ice-field 

 connected with it ; while Prof. Nordenskiold's excursion was made 

 at a place too far south to afford an accurate idea of the actual con- 

 dition of the interior of North Greenland, even though he had pene- 

 trated much further than he actually did. However, the state of 



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