INTERNATIONAL GEOLOGIC INSTITUTE 6oi 



assigned to the same period, though they have no species in 

 common, and the other stages will fall into their proper sequence. 

 This may suffice to illustrate one method by which the migra- 

 tion, and particularly the cross-migration, of faunas maybe brought 

 into service in the correction of the errors of correlation arising 

 from dependence simply on the presence of common fossils. 

 It will furthermore be recognized with acclaim that the tracing 

 out of the origins and migrations of the ancient races of the 

 earth's inhabitants has independent and profound interest, and 

 that it is peculiarly and necessarily an intercontinental work. 



But the origin and migration of faunas and floras is pecul- 

 iarly dependent on physical conditions. I am persuaded that 

 this is most eminently true of the origin of provincial faunas and 

 their evolution into cosmopolitan faunas, as I have endeavored 

 to set forth in. recent papers. 1 While it will doubtless always be 

 quite difficult to detect the point of origin and the course of 

 migration of single species, there is reasonable ground of hope 

 that the origin of provincial faimas may be located, and their 

 migrations and fusions followed until they are lost in cosmo- 

 politan faunas. I have given reasons elsewhere for believing 

 that the general production of provincial marine faunas of the 

 shallow-water type is connected with the withdrawal of the sea 

 from the upper face of the continental platforms, associated with 

 surface warpings, by the first of which the areas of shallow water 

 are restricted, and by the second dissevered from each other. 2 

 It is therefore believed that much aid in rendering paleonto- 

 logic interpretations more significant, more certain, and more 

 precise may be derived from the study of the bodily move- 

 ments of the earth and of the evolution of the geography of the 

 continents in their migratory relations. Certainly and admittedly 



111 The Ulterior Basis of Time Divisions and the Classification of Geologic His- 

 tory," Jour. Geol., Vol. VI, No. 5, July-August 1898, pp. 449-526. 



"A Systematic Source of Evolution of Provincial Faunas," Jour. Geol., Vol. V, 

 No. 6, Sept.-Oct., 1898, pp. 597-608. 



"The Influence of Great Epochs of Limestone Formation on the Constitution of 

 the Atmosphere," Ibid., pp. 609-621. 



2 The first two papers above cited. 



