T6 T. Mellard Eeade — Oceanic Islands. 



present contours of onr continents, would have been submerged 

 to about the 700 feet contour. It is impossible at present to calcu- 

 late with exactness to what extent this would reduce its surface, but 

 probably one-half. If, on the other hand, the land had risen since 

 Cambrian times 1500 feet, it is evident there must have been very 

 little of it to commence with. Therefore, if there has been a 

 pi'eponderance of depression in the oceans and of elevation in the 

 land since Cambrian times, it has acted within very narrow limits, or 

 there would not have existed land enough to provide sediment for the 

 construction of the enormous thickness and extent of the later 

 sedimentary rocks we know of, to say nothing of those which 

 under my hypothesis must be admitted to extend more or less under 

 the sea-bed. 



The volcanic oceanic islands are mostly based upon submarine 

 plateaux, one of which in the Pacific extends from Cape Horn in a 

 north-westerly direction to Tahiti, a distance of some 80 degrees of 

 longitude and 30 degrees of latitude, at a depth of about 1000 

 fathoms.^ It is conceivable, if these plateaux were areas of oscilla- 

 tion of level, that the vertical limits of movement may have been too 

 small to have produced by that means continental islands, and it is 

 also conceivable, though not jDrobable, that the plateaux may now all 

 be at the downward limit of oscillation." Now comes my argument. 



The lapse of time between the Cambrian and Tertiary periods was 

 vastly greater than that between the commencement of the Tertiary 

 and the present time. I will not presume to say how much more, 

 because authorities differ, but Dana puts it down, as nearly as I can 

 interpret him, at about fifteen times as great.^ Are we then to 

 assume that during all this vast interval of time, and over an 

 immense extent of the ocean floor, the volcanic forces of the earth, 

 which some physicists maintain have been gradually dying out, lay 

 dormant, so that no volcanic island or land was built up from even 

 a depth of 1000 fathoms — not two-thirds the height of Etna ? And 

 are we to go further, and say that this stable state of equilibrium 

 was suddenly disturbed by volcanic eruptions during and since the 

 Tertiary period, by which what are called the Oceanic islands were 

 created? I think neither physicists nor geologists will admit this 

 to be probable without very strong evidence, Avhich has yet to be 

 given. 



It may be said in repl}"^ that such Palaeozoic or Secondary volcanic 

 islands may have existed and become since destroyed by atmospheric 

 or oceanic waste; but this admitted, cuts the ground from under the 

 argument, as the same forces would also have destroyed sedimentary 

 rocks, the absence of which is accounted a proof of the permanence 

 of the oceans and continents. 



Properly considered, then, the argument drawn from the volcanic 

 or non-sedimentary nature of the so-called oceanic islands is, as 

 usual with negative evidence, not very much to be relied on. Nay, 



1 Thalassa, pp. 21-2. 



2 This is disproved by Dr. Darwia's own observations. 

 2 Manual of Geology, 2nd edit. p. 586. 



