190.S] 0)1 the Figure and Gonditution of the Earth. 105 



of some of the most important changes that can have been produced 

 by g-ravitational causes, by leaving this iuequaHty out of account. 

 We seek then the changes that can have been produced by the actual 

 diminution of the inequality of the first degree, resulting in an increase 

 of the relative prominence of the inequality of the third degree. 

 The changes, being of the nature of the relief of strain, must take 

 place somewhat spasmodically, l)ut at any one place they would be 

 progressive, not fluctuating, and we should expect that the actual 

 reduction in the inequality of the first degree would be greatest where 

 the inequality is greatest, that is near the centres of the two hemi- 

 spheres, where it gives us elevation and depression respectively. The 

 regions where the computed elevation is greatest contains the 

 Mediterranean and adjacent seas. The idea of a progressive diminution 

 in the amount of the first harmonic suggests, that the formation of 

 these seas, and of the neighbouring mountain ranges, is not to be 

 ascribed entirely to a series of tectonic accidents, but that these move- 

 ments were at least in part conditioned by a gravitational change. The 

 increase in the relative prominence of the third harmonic would bring 

 it about that where the first harmonic gives us elevation and the third 

 depression oceans might be formed, and, if formed, they would get 

 wider and deeper with the lapse of time. This state of things is 

 found in the Arctic, Atlantic and Indian oceans. Where ancient con- 

 tinents are destroyed by inundation we should expect that some rem- 

 nants would survive to mark the ancient sites. In such places the 

 computed elevation would be apt to be too small. This is the case, 

 for example, in South Africa, West Africa, Brazil and the north- 

 eastern part of North America. On the other hand, where the first 

 harmonic gives us depression and the third elevation, there would be 

 a tendency for the continental region to encroach upon the oceanic. 

 This state of things is found around the shores of the Pacific, espe- 

 cially on the American side, and on the greater part of the coast of 

 Australia. Where an ancient ocean is contracted by retreat of the 

 sea, we should expect to find that in some parts the new elevation 

 would fail to be formed and the sea would retain its mastery. In such 

 places the computed elevation w^ould be apt to be too great. This is 

 the case for example, between Australia and the Antarctic continent 

 and to the west of Central and South America. It appears that a 

 change in the actual amount of the inequality answering to the first 

 harmonic, combined with an increase in the relative prominence of 

 the inequality answering to the third harmonic, accounts foi* most of the 

 defects of the theoretical map obtained by combining harmonics. 

 [The statement was illustrated by two maps shown as slides.] The 

 conclusion that the Atlantic and Indian Oceans are modern in com- 

 parison with the Pacific, is one to Avhich geologists have been led by 

 independent evidence, and the differing characters of the coasts around 

 the two great ocean basins has been especially emphasised by Suess. 

 The difference consists in the relations of the coasts to the mountains. 



