V.—The Thickness of the Ice-Cap in the various Glacial Periods

Extract

In estimating the maximum load which pressed upon the northern type of Glacial (Dwyka) Conglomerate in Prieska, Cape Colony, I assumed that the calculations of Sir Wyville Thomson and Bernacci were correct, and that the greatest column of ice that could exist on the earth's surface was from 1,400 to 1,600 feet high. This limit, however, is by no means accepted by European glacialists, who, though they do not go as far as Dr. Croll in assuming thicknesses of 120,000 feet, yet see no reason why there could not have been ice-sheets 5,000 feet thick. The publication of Captain Scott's narrative of the voyage of the “Discovery” has given us certain definite data from the Antarctic which enable the case for the 1,600 feet maximum to be put with more confidence, and I will endeavour in the present paper to state the main lines of the argument. The question is of importance not only to us in South Africa with our two Palæozoic ice-ages, but to all geologists, as it affects the problem of the earth's equilibrium. To give a recent example, Professor Penck, in describing the Bodensee, discusses whether the weight of ice pouring down from the Alps in a sheet 3,600 feet thick may not have had some effect in producing a sinking in the earth's crust.