Crosby.] 474 [November 7, 



central ocean has been at one time a marginal sea-bottom and the 

 theatre of active and extensive deposition. This means that a 

 large part of the deep sea-bottom has formed not only the 

 shoulders but the dry land of the continents. 



If, as those believing in stable continents and oceans virtually 

 claim, the oceanic portions of the earth's crust have been covered 

 since the beginning of geological time with a sheet of cold water, 

 the frigid zone extending, along the ocean-floor, through all lati- 

 tudes to the equator; and if, during the whole of geological his- 

 tory, deposition has been almost entirely suspended over these 

 vast areas, the sediments of probably not less than a million years 

 being insufficient to cover the teeth of the Eocene shark ; then, 

 since the strength and thickness of the earth's crust are, in the 

 main, due to, and are a measure of, the refrigeration which it has 

 experienced, it must be admitted that the oceanic crust is proba- 

 bly very thick and very stiff. That sediments are in general a 

 source of weakness rather than of strength in the crust is the tes- 

 timony of the ablest students of structural geology; and this 

 proposition forms the basis of the generally accepted explanation 

 of the origin of mountains. 



Now, if volcanoes are evidence of anything, they are evidence 

 of weakness in the earth's crust. They prove the presence of fis- 

 sures reaching down to the plastic zone beneath the crust ; and, 

 as we have already noticed, they are, on the land, intimately con- 

 nected with thick deposits of sediments — with what are gener- 

 ally recognized as weak places in the c^ust. But it is a logical 

 deduction from the hypothesis here combatted that the numerous 

 oceanic volcanoes do not stand on thick accumulations of sedi- 

 ments — for no deposits of sensible thickness are formed in the 

 deep sea, and that they occur on the strongest, rather than the 

 weakest, portions of the earth's crust — for nowhere are the con- 

 ditions more favorable for deep and permanent refrigeration of 

 the crust than under the oceanic abysses and, according to Mr. 

 Wallace and Professor Dana, the site of the deep sea has re- 

 mained unchanged during all the changes of which geology fur- 

 nishes a record. 



Professor Dana says the oscillations of the sea-floor are slight 

 compared with those of the land, the principal movement being a 

 gradual subsidence running through the ages which may be 



