546 F. H. KXOAVLTOX EYOLUTIOX OF GEOLOGIC CLIMATES 



Ulrich also adds that there is undoubted evidence, notably in the early 

 Cambrian and early in the Pennsylvanian, when ''frigid conditions oc- 

 cnrred at least locally." This is the very crux of the matter, for it seems 

 clear that while there are undoubted evidences of glaciation. they were, 

 at least for the most part, so very local in their effect that they seem to 

 have made little impress on the temperature of the oceans, and hence 

 on tlie continuity and distribution of marine life. As bearing on this 

 point. Dr. John M. Clarke has expressed his opinion as follows: 



'•There is of course pleuty of evidence of cold weatlior periods and also of 

 local cold tlirougliout Paleozoic history. I can not say that such determina- 

 tions are, in any single particular within my knowledge, dependent upon the 

 fossils of the rocks: nor can I say that the obvious evidences of recurrent 

 land glaciation are connected in any way with or supported by any facts pro- 

 ducible from coexistent faunas or floras. I have worked out with some par- 

 ticularity a somewhat circumscribed glaciation in the later stages of Devonian 

 time. That it has had any effect on the marine faunas I can not say : whether 

 it has affected the estuarine or river faunas represented by the Devonian 

 fishes, we can not tell because we are not able to deduce from their data the 

 adaptations of those creatures." 



The present average temperature of the surface of the oceans varies 

 from about — l.T° C. at the poles to about 2^.88° C. in the warmest 

 (Indian) ocean. The average surface temperature of the oceans as a 

 whole is as follows: Atlantic, 16.9° C. : Pacific, 19.1° C. : Indian, 17° C. 



It is, of course, well known that water is a very poor heat conductor. 

 According to Grabau. it has been calculated 



"that a mass of water 5.0(X) meters deep, and of a uniform temperature of 

 0" C, would, if m contact with a heat source of 30= C. at the surface, experi- 

 ence the following rate of warming, providing no other factor, such as con- 

 vection currents, etc.. entered in. In 100 years no appreciable increase in 

 temperature would be found at a depth of 100 meters; in 1,000 years not one 

 per cent of the surface warmth is to be found at a depth of 300 meters, while 

 it takes 10,000 years to carry this: fraction of the surface warmth to a depth 

 of 1.000 meters, and 1,000.000 years to carry it to a depth of 1.900 meters. 

 After 1.000 years the temperature at a depth of 100 meters will be 7.3° C, 

 while at 200 meters it will be only 0.6= C."" 



In actual practice, however, the warming of a body of water is more 

 rapid, due to the absorption of the sun's rays, vertical convection cur- 

 rents, and the sinking of heated saline waters whose density has been 

 increased by the surface evaporation; but at best the process is a slow 

 one. If, as has now been demonstrated, the process of heating up a great 

 bodv of water is such a slow one, it must follow that it will give tip its 

 heat with an approximate degree of slowness. Xow, the very pertinent 



