24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



c. g., Guppv, are inclined to consider the South Equatorial as hipartite 

 throughout, calling the Guiana current the Main Equatorial current. 

 The point is immaterial in the present connection since all I desire 

 to show is that the shape of eastern South America and the latitude of 

 Cape San Roque are purely fortuitous in so far as their relation to 

 climate is concerned, and yet if the latter had happened to lie a few 

 degrees north of its present position much of the water that ultimately 

 contributes to the Gulf Stream would have turned southward to aug- 

 ment the P)razilian current, and the climate, especially of Europe and 

 the Arctic, would he profoundly modified. It has been estimated that 

 if Cape San Roque were 2° north of its present position there would 

 he a shift of Jfi'/v of the E(juatorial current which would be deHected 

 southward instead of northward. The same results would be attained 

 if the southern trades were not stronger and more constant than the 

 northern trades, because of the relative amounts of land and water 

 in the northern and southern hemispheres. 



Scant attention will be devoted to the various theories that have 

 been advanced to explain geological climates. These range from that 

 of Croll, in its original or modified form, based upon the eccentricity 

 of the earth's orbit and the obliquity of the ecliptic, which was doubt- 

 less a factor at all times, but hardly a controlling one; through those 

 theories that rely on changes in the atmosphere, such as alterations 

 in the amount of carbon dioxide (Tyndall, Arrhenius, Chamberlin)' 

 amounts of volcanic dust (Humphreys), to the extreme form of the 

 hypothesis advanced by Manson, and elaborately defended by Knowl- 

 ton, that a combination of cloudiness progressively diminishing dur- 

 ing earth history, and a terrestrial control due to a cooling earth, 

 instead of a solar control as at present, are the primary factors which 

 explain past climates. Finally there are those highly speculative 

 hypotheses such as Chamberlin's reversal of the oceanic circulation, 

 and a group which predicate a wandering of the poles in various 

 ways, now fashionable in the revived form put forward by Wegener. 



I have quite possibly omitted other proposals that might be men- 

 tioned, and I have now to mention the theory, if it can be called a 

 theory, which is the main thesis of the present paper, namely : that 

 it seems to me possil)le to interpret geological climates in the light of 

 demonstrated changes in topography and geography, including under 

 the latter differences in the distribution of land and water and the 

 transfer of energy by currents. 



^It is of interest to note that Neumayr in 1883 pointed out that excesses of CO2 

 would be impossible since the absorption by the oceans would maintain an almost 

 perfect balance. 



