1906] 



OF DEEP-SEA CIRCULATION. 35 



a gaseous or quasi-gaseous nebula through gravitative condensa- 

 tion. To some of us, however, such a derivation seems inconsistent 

 with the dynamics of the present solar system, and an alternative 

 hypothesis has been formulated to meet the supposed requirements 

 of existing phenomena. The acceptance of this requires a recon- 

 struction of the wdiole conception of -geologic climates. The new 

 view discards the primitive molten state as a necessary condition 

 and presents the alternative of a slow growth of the earth by planet- 

 esimal accessions. This alternative involves a slow growth of the 

 atmosphere also, until it reached a volume similar to the present, 

 when its growth is assumed to have been arrested and thereafter 

 limited by the interplay of opposing agencies. These agencies are 

 thought to have held it ever since within so narrow a range of 

 oscillation as to foster organic evolution. A continuance of the 

 same control offers ground for hope of a perpetuation of conditions 

 congenial to organic and intellectual life, through a period to which 

 no definite limits can now be set beyond the presumption that there 

 must ultimately be a limit. The inevitable cooling of a once white- 

 hot earth plays no part in this prognosis. The agencies of atmos- 

 pheric maintenance and control thus force themselves upon consid- 

 eration as factors of supreme importance. 



The assigned agencies of atmospheric restraint are molecular 

 velocities, chemical combination and condensation. By virtue of the 

 first, the lighter constituents are reduced to a minimum and all con- 

 stituents are restricted within certain large limits. By virtue of 

 the second, the chemically active factors are kept down to states of 

 dilution compatible with organic evolution, while the inert elements 

 have probably been permitted to increase steadily. By the third, the 

 excess of water-vapor has been condensed into the ocean, which has 

 probably increased rather than diminished through the ages. 



The postulated agencies of atmospheric supply are accessions 

 from without and emanations from within, of which \>suvius is 

 just now giving us an impressive illustration. 



To the interplay of these opposing agencies of loss and gain is 

 assigned the maintenance of the requisite narrow range of atmos- 

 pheric constitution, of temperature, and of associated conditions. 

 Under this general resetting of fundamental conceptions, the ques- 



