Febeuaet 18, 1910] 



SCIENCE 



243 



geography, geology, oceanography, climat- 

 ology, paleontology and evolution. The 

 principles of astronomy, physics, chemis- 

 try and biology are also involved to the ex- 

 tent that they enter into the development 

 of geographic conditions. 



Because paleogeography is thus compre- 

 hensive, no one investigator can adequately 

 solve its problems. A group of students 

 only can do the science justice. In at- 

 tempting this statement of its general prin- 

 ciples, I do not fail to recognize the fact 

 that it must be incomplete and qualified by 

 inadequate understanding of many of the 

 branches of knowledge involved. 



PEEMANENCE OF OCEAN BASINS 



Oceanography is a science which as yet 

 scarcely ventures over the threshold of the 

 present upon the long vista of the past, but 

 the guidance of paleogeography leads that 

 way. From the study of ancient lands and 

 epicontinental seas we are led directly to 

 the recognition of ancient ocean basins; it 

 is, however, particularly among European 

 geologists, still a mooted question whether 

 the hollows, which the waters occupy, have 

 constantly existed as hollows or may have 

 been sites of continents which have now 

 sunken in. The evidence that the hollows 

 have constantly existed is strong. Upon 

 it rests an assumption, which must be 

 either affirmed or denied, there being no 

 third condition, and which may be stated 

 in the affirmative form as a principle : 



The great ocean hasins are permanent 

 features of the earth's surface and they 

 have existed, where they noiu are, with 

 moderate changes of outline, since the 

 waters first gathered. 



This conclusion rests upon three princi- 

 pal facts : 



The continents have never been sub- 

 merged to oceanic depths and consequently 



can not have been replaced by deep hol- 

 lows. 



The oceanic basins have always been of 

 such capacity that they contained by far 

 the larger part of the waters, which have 

 overflowed on the continents only as rela- 

 tively shallow epicontinental seas; hence 

 no considerable pai-t of the existing basins 

 can ever have been occupied by land. 



There is a relation between the intensity 

 of gravity and the relative altitude of a 

 continental or oceanic plateau, which 

 proves that the plateaus have assumed 

 different altitudes according to the densi- 

 ties of the subjacent material. The trans- 

 formation of a continent into an ocean 

 basin, or vice versa, would require, there- 

 fore, a change in density of an enormous 

 volume of material, and there is neither 

 evidence nor explanation of such a change. 



A few words may be said in support of 

 these propositions, but before doing so a 

 distinction should be made between the 

 great ocean basins and those deep troughs 

 which have from time to time developed 

 within continental plateaus and which 

 Dana called geosynclines. 



In their genesis ocean basins and geo- 

 synclines may have been similar; but in 

 their dimensions, histories and structural 

 relations they are radically different. 



I will not dwell on the great magnitude 

 of the Atlantic or Pacific basins in compar- 

 ison with the Appalachian or Cordilleran 

 geosynclines. They need but be named. 



The history of a geosyncline comprises 

 a prolonged stage of subsidence accom- 

 panied by more or less constant deposit of 

 terrigenous or marine sediment, and often 

 a further stage of compression, folding of 

 strata and elevation as a mountain range. 



The history of ocean basins does not ex- 

 hibit a similar stage of subsidence within 

 the eras of the geologic record, although 

 the hollows have sometimes apparently 



