IfH) ANNALS NEW YORK ACADEMY OF SCIENCES 



probably derived frotn imsubmerged adjoining portions of the existing 

 continents. We are apt to assume that great displacements of strata in- 

 volve correspondingly great changes of level. They do not necessarily: 

 more proliably, in most instances, the erosion has kept pace more or less 

 closely with the displacement. Even where great changes of level have 

 occurred, thev often have been, and more often mav have been, of re- 

 stricted extent and compensated by opposite changes in regions imme- 

 diately adjoining, and most of them have had but little extensive or 

 permanent effect on the general configurations and relations of the conti- 

 nental platforms. 



Tlie relative permanency of the Xorth American continent is very 

 clearly brought forward in Schuchert's maps.^*' Yet even here, if one 

 may venture a criticism on so thorough and conservative a study, there is a 

 certain loss of conservatism where the outlines run into territory where 

 the evidence is inadequate, as in the Antilles and the Arctic seas. The 

 imperfect data available for the South American continent appear to in- 

 dicate general conditions verv similar to those of its northern neighbor ; 

 nor does it appear that Africa and Australia were any less permanent 

 land platforms. Northern Eurasia appears to have been similarly perma- 

 nent, but across Central Europe and extending southeastwardly to the 

 East Indies lies a broad strip of disturbance where great changes have 

 occurred during later geologic time. But the extent and permanency of 

 the great central sea which is so frequently depicted as interposing a 

 broad ocean between the Holarctic and the Ethiopian and Oriental land 

 masses is by no means certain, especially as regards its eastward exten- 

 sion. I cannot find in the recorded facts proof that it afforded any more 

 continuously effective bar to dispersal along the lines of the present con- 

 tinental relations than did the middle Cretaceous overflow in North 

 America or the early Tertiary one in South America. 



Perhaps the most widely accepted departure from the permanency of 

 the ocean basins is the supposed Gondwana Land, invented to account 

 for certain similarities in southern Paleozoic floras, and since used to 

 account for almost all cases of similarity among southern florae and faunae 

 Miiich were not demonstrably due to dispersal from the northern conti- 

 nent. This theory has in its original form gone so long uncontested that 

 it is very generally regarded as incontestable. New discoveries have been 

 interpreted in terms of it, the weakness of the original evidence, the pos- 

 sibility that it might be otherwise interpreted, has been forgotten, and 

 like the Nebular Hypothesis, it has become almost impossible to dislodge 

 it from its place in the affections of the average geologist. 



Cii.\nLKS Si iiichkrt: BuH. (!eol. Soc. Amer.. vol. L'O. pp. 427-006. pll. xlvi-ci. 1910. 



