190 A. P. COLEMAN DRY LAND IN GEOLOGY 



differently arranged ? Large amounts of water are withdrawn from cir- 

 culation by the hydration of various minerals. Are they balanced by the 

 amounts restored as juvenile waters and the steam from volcanoes, assum- 

 ing, of course, that volcanoes give off steam and not ammonium chloride ? 

 Probably most geologists take it for granted that the amount of water on 

 the globe is nearly constant from age to age. 



The existence of dry land at all when there is so much water on the 

 earth is a profound mystery not even plausibly explained by the nebular 

 hypothesis, since it demands an inexcusable irregularity in the working 

 of the nebular machinery. 



Have Oceans and Continents ever changed Places? 



Admitting that in the beginning the lithosphere bulged up in places, 

 so as to form continents, and sagged in other places, so as to form ocean 

 beds, there are interesting problems presented as to the permanence of 

 land and seas. All will admit marginal changes affecting large areas, but 

 these encroachments of the sea on the continents and the later retreats 

 may be of quite a subordinate kind, not implying an interchange of deep 

 sea-bottoms and land surfaces. The essential permanence of continents 

 and oceans has been firmly held by many geologists, notably Dana among 

 the older ones, and seems reasonable ; but there are other geologists, espe- 

 cially paleontologists, as Avell as zoologists and botanists, who display 

 great recklessness in rearranging land and sea. The trend of a mountain 

 range, or the convenience of a running bird, or of a marsupial afraid to 

 wet its feet, seems sufficient warrant for hoisting up any sea-bottom to 

 connect continent with continent. A Gondwana Land arises in place of 

 an Indian Ocean and. sweeps across to South America, so that a spore- 

 bearing plant can f oIIoav up an ice age ; or an Atlantis ties New England 

 to Old England to help out the migrations of a shallow-water fauna ; or a 

 "Lost Land of Agulhas" joins South Africa and India. 



It is curious to find these revolutionary suggestions made at a time 

 when geodesists are demonstrating that the earth's crust over large areas, 

 and perhaps everywhere, approaches a state of isostatic equilibrium, and 

 that isostatic compensation is probably complete at a depth of only 76 

 miles. Ha} r ford's results have been ably supported and applied by my 

 predecessor, Doctor Becker, in his address last year; but some geologists 

 hesitate to accept them. Barrell, after an elaborate discussion of the 

 whole question, thinks the equilibrium much less complete than Hay- 

 ford's results would suggest ; but his arguments do not seem entirely con- 

 vincing. 17 Great stress is laid on the submarine deltas of the Nile and 



17 Articles on the strength of the earth's crust. Jour. Geol., vols, xxii and xxiil. 



