.8,,. E VOL UTION OF OCEA NS A ND CONTINENTS. 5 1 1 



portions of the eartli's crust which have been subjected to the greatest 

 pressures and disturbances ; while the deeper parts of the ocean 

 are probably those where the crust has long been in a state of 

 tension and comparative quiescence. It is true that the tension 

 might, and probably has, led to the production of faults ; but the 

 faults developed at any one epoch would be small, and if they formed 

 a system of trough-faults the surface features produced would be 

 quite insignificant. (5) Lastly, if there be any truth in Mr. Fisher's 

 idea of the frequency of sub-oceanic outpourings of lava, such extra- 

 vasations would largely account for the comparative smoothness of the 

 ocean floor. 



Here, so far as Dr. Wallace's arguments are concerned, I might 

 leave the subject, but I wish to make a further suggestion, and, 

 following Dr. Wallace's example, to advance another a priori 

 consideration. 



All who have hitherto discussed the question of the permanence 

 of oceans have done so on the basis of the present physical conditions 

 of the globe, and have assumed that the volume of ocean water, and 

 consequently the mean depth of the ocean, have always been the 

 same. But are we justified in making this assumption ? 



The Rev. Osmond Fisher has done a great service to the science 

 of Geology in showing that the contraction theory is totally inadequate 

 to account for the inequalities of the earth's surface, and in placing 

 the hypothesis of a thin crust with a liquid substratum upon a sound 

 basis by his suggestion that water in the state of gaseous matter is 

 associated with the liquid magma. In this way he explains the pre- 

 sence of water among volcanic products, which has always been a 

 physical difficulty. But, if his theory be true, it follows that every 

 eruption which has taken place on the globe during the long ages of 

 past time has contributed a certain amount of water to swell the 

 volume of the ocean. Hence the oceans have been gradually 

 increasing in depth and extent throughout all geological time, and 

 the area of the land has been as gradually diminished. 



If, therefore, we accept this hypothesis (and it affords by far the 

 most satisfactory basis for the explanation of terrestrial physics that 

 has yet been imagined), we must look back to a time when the oceans 

 were very much smaller and shallower than they are now. Further, 

 if we accept Mr. Fisher's view of the manner in which continents 

 and mountain chains have been ridged up by the pressure of the 

 horizontal connection-currents in the substratum, it seems probable 

 that there has been a tendency toward the condensation of land 

 masses into continental areas, and we may look back to a time when 

 the continental plateaux did not rise so high above the mean level of 

 the ocean floor as they do now. 



It would appear, then, that a geologist is justified in supposing 

 the total area of land in early Palaeozoic time to have been equal to 

 or greater than that of the sea, both being more equally distributed, 



