324 



SCIENCE. 



[N. S. VOT.. V. No. 113. 



tive, and therefore the more rapidly cooling 

 and contracting areas. This would again 

 increase, and in this case progressively in- 

 crease, the depression of these areas. The 

 two causes — destiny and conductivity, 

 isostasy and contraction — would concur, 

 but the latter would he far the greater, be- 

 cause indefinitely cumulative. The origi- 

 nally evenly spheroidal lithosphere would 

 thus be deformed or distorted, and the dis- 

 toi'tion, fixed by solidification, would be 

 continually increased until now. When 

 the earth cooled sufficiently to precipitate 

 atmospheric vapor the watery envelope 

 thus formed would accumulate in the basins 

 of the lithosphere and form the oceans. It 

 is possible, and even probable, that the de- 

 pressions were at first so shallow that the 

 primeval ocean may have been universal, 

 but the process of greater downward con- 

 traction continuing, the ocean basins would 

 become deeper and the less contracted por- 

 tions of the lithosphere would appear as 

 land. The process still continuing, the 

 land would grow higher and more exten- 

 sive and the ocean basins deeper and less 

 extended throughout all geological time. 

 On the whole, in spite of many oscillations, 

 with increase and decrease of land, to be 

 spoken of later, and in spite, too, of exterior 

 agencies by erosion and sedimentation tend- 

 ing constantly to counteract these effects, 

 such has been, I believe, the fact through- 

 out all geological history. 



It is evident, also, that on this view, since 

 the same causes which originally formed the 

 ocean basins have continued to operate in 

 the same places, the positions of these 

 greatest inequalities of the lithosphere have 

 not substantially changed. This is the 

 doctrine of the permanency of oceanic basins 

 and continental masses, first announced by 

 Dana. Some modification of this idea will 

 come up under another head. 



The objection which may be — which has 

 been — raised against this view is that such 



heterogeneity as is here supposed, in a fused 

 mass and therefore in a mass solidified 

 from a state of fusion, is highly improbable, 

 not to say impossible. This objection, I 

 believe, will disappear when we remember 

 the very small differences in conductivity, 

 and therefore in contraction, that we are 

 here dealing with; small, I mean, in com- 

 parison with the size of the earth. This is 

 evident when we consider the inequalities 

 of the earth's surface. The mean depth of 

 the ocean is about two and one-half miles ; 

 the mean height of the land, about one- 

 third of a mile. The mean inequality of 

 the lithosphere, therefore, is less than three 

 miles. This is xsVt ^f the radius of the 

 earth — less than y^^ of an inch (an almost 

 imperceptible quantity) in a globe two feet 

 in diameter. I believe that a perfectly 

 spheriodal ball of plastic clay allowed to dry, 

 or even a spheriodal ball of red-hot copper 

 allowed to cool, would show more deforma- 

 tion by contraction than the lithosphere of 

 the earth in its present condition. It is true 

 the inequalities are more accentuated in 

 some places, especially on the margins of 

 the continental areas; but this is due to an- 

 other cause, mountain-making, to be taken 

 up later. 



Another objection will doubtless occur to 

 the thoughtful geologist. It would seem at 

 first sight on this view that ocean areas 

 cooling most rapidly ought to be the first to 

 form a solid crust, and the crust (if there 

 be any interior liquid still remaining) ought 

 to be thickest, and therefore least subject to 

 volcanic activity, bhere ; but, on the con- 

 trary, we find that it is just in these areas 

 that volcanoes are most abundant and ac- 

 tive. It is for this reason that Dana be- 

 lieved that land areas were the first and 

 ocean areas the last to crust over. This is 

 probably true ; but a little reflection will 

 show that these two facts, namely, the 

 earlier crusting of the land areas and the 

 more rapid cooling and contraction of the 



