THEORIES REGARDING THE EARTH's INTERIOR. 24I 



the recent work of Jean's, it is found that the earth is pear- 

 shaped with the stalk end in Africa and the bhnit end in the 

 Pacific. The reason for this shape is that nowdiere else in 

 the globe are the sedimentary rocks of post-Archaean age so 

 thinly developed: for immense periods the Continent of Africa 

 has been practically uncovered by the sea. and as a conse- 

 quence, wdiere the rest of the crust has been burdened by 

 thicknesses of strata representing billions of tons. Africa has 

 stood free, Hence, whereas the rest of the globe has_ been 

 depressed, Africa has been bulged out beyond the limits of 

 the sphere. 



In piercing the rocks in Africa we therefore penetrate deeper 

 into the earth's interior than in any other part of the globe, 

 and we find that the temperature increment, instead of being 

 anything like the average of i° F. for every 60 feet, is 1° F. 

 for every 225 feet on the Rand. 



There' are of course other areas of low temperature incre- 

 ment in the globe, such as the granite area of ^^linas Geraes 

 in Brazil, also a region of granite and gneiss thinly covered 

 with sediments, but nowhere else than in Africa is such a vast 

 area of low temperature increment to be reckoned on. If 

 the height of the bulge of Africa above the spherical surface 

 be taken at five miles this would mean that in five miles the 

 temperature increment has fallen from 1° F. for every 60 ft. 

 to 1° F. in 225 feet. 



It is, 'however, impossible to reduce the observations to 

 scale in this way; a contemplation of the rates of increase at 

 various places given in any of the lists makes it quite obvious 

 that no prediction of temperature increase at one place can be 

 made from observations at another, as we have seen was done 

 with unfortunate consequences in the case of the Simplon 

 tunnel; in the British Isles alone the temperature increment 

 vary from 1° F. for every 34 feet to 1° F. for every 130 feet; 

 but, taking all the variations into account, there is sufficient 

 evidence from the observations to bear out the contention that 

 the nearer the interior of the globe the less is the temperature 

 increase for equal distances. This has been long recognised 

 and reg'arded as an insoluble enigma, but in the light of modern 

 geological thought it is not only not an enigma but a neces- 

 sary consequence. 



The belief in a hot interior of the globe has so possessed 

 the minds of people, that when deep level mining is proposed, 

 the public still cling to the belief that it must be impossible 

 because their geological text books say that at such depths 

 the temperature would be prohibitive to working. I venture 

 to trust, therefore, that a more widespread knowledge of 

 Chamberlin's planetismal hypothesis and the developments 

 that have appeared since its publication are not only of 

 academic interest, but have an important bearing on the 

 economic w^elfare of this country. I have. I am afraid, out- 

 lined a number of contentious arguments, but the intention 

 of this paper is more to call attention to the trend of modern 

 investigation in Geology than to prove each step, and I have 

 elsewhere dealt with the whole subject in cxtcuso. 



