602 T. C. CHAMBERLIN 



this is eminently true of land faunas whose migrations are essen- 

 tially dependent on terrestrial connections, and I believe it is 

 scarcely less true that the migration of the more immobile por- 

 tion of shallow water sea faunas is dependent on continental 

 shelves and epicontinental seas. If, therefore, there be a peri- 

 odicity in the great bodily movements of the earth and sea, and 

 a consequent periodicity in the origination of provincial faunas, 

 there will be all the greater field for the application of principles 

 founded on migration and counter-migration to the working out 

 of more precise correlations. 



(#) There is reason to hope that the sea itself may be made 

 an important aid in intercontinental correlation, for it makes, 

 and always has made, a simultaneous record on all the continents. 

 The difficulties lie solely in reading the record. 



The ocean volume may not have been accurately constant at 

 all times, but its variations between closely related periods can 

 never have been more than a negligible fraction of the whole 

 volume. Its record is made on the border of a single complex 

 basin, for all the oceans are united and have a common water level. 

 Apparently there has always been essentially a single complex 

 basin, though this cannot be rigorously affirmed. Assuming it, 

 however, any deformation of the basin in any part, which affects 

 its capacity, is recorded on all continents by a new shore line. 

 Setting aside compensatory warpings, this involves a universal 

 advance or retreat of the sea, and a corresponding change in the 

 areas of sedimentation and erosion. It involves, also, a change 

 of land and sea faunas by expanding and contracting their habi- 

 tats respectively, and by extending or restricting their means of 

 migration. Were it not for the attendant warpings of the land, 

 these sea changes would furnish a simple means of world-wide 

 correlation of the most precise and specific kind. Conjoined 

 with paleontology they would leave little to be desired so far as 

 marine stages are concerned. There remains, however, the 

 problem of eliminating the disturbing effects of concurrent 

 warping. To some large extent it is the warping that changes 

 the capacity of the ocean basins. Warping may even disturb 



