104 Dr. J. Croll on the Physical Theory 



equator; hence when they are impelled against the American 

 and the Asiatic continents, and become deflected northwards 

 and southwards, the larger portion of the water goes to the 

 north, and thus raises the temperature of the northern hemi- 

 sphere. Now if all this results as a consequence from the 

 present small amount of eccentricity, how much greater must 

 have been the effect during the glacial epoch, when the 

 eccentricity was more than three times its present value and 

 the southern winter also, as now, in aphelion ! All those effects 

 which we have just been considering would then have been 

 magnified far more than threefold. 



Climatic Conditions of the two Hemispheres the Reverse 

 10,000 or 12,000 years ago : Argument from. — Ten or twelve 

 thousand years ago, when our northern winter solstice was 

 last in aphelion, the climatic conditions were in all probability 

 the reverse of what they are at present. There appears to be 

 pretty good geological evidence that such was the case. This, 

 under the present small amount of eccentricity, shows not 

 only to what an extent climate is affected by eccentricity, but 

 also (and with this we are at present more particularly con- 

 cerned) that its tendency is to cool the one hemisphere and 

 warm the other, to accumulate the snow and ice on the one 

 and melt them on the other. And this result, to a large ex- 

 tent, is doubtless brought about by its influence on ocean- 

 currents. 



There are good reasons for concluding, as Prof. J. Geikie 

 has fully shown *, that at a very recent date (during the time 

 of the formation of the 40-feet raised beach and the depo- 

 sition of the Carse-clays) the climate was much colder than 

 it is at present. The seas surrounding our Island appear to 

 have had a lower temperature than they have at present; and 

 our Highland valleys seem to have been occupied by local 

 glaciers t- 



The Carse-clays of Scotland are best developed in the 

 valleys of the Tay, the Earn, and the Forth. These deposits 

 consist of finely laminated clays and silt. " Now and again," 

 says Prof. J. Geikie, " the deposits consist of tough tenacious 

 brick-clay, which does not differ in appearance from similar 

 brick-clays of glacial age." The clay is usually free from 

 stones, but occasionally blocks of six inches or a foot in 



* i Prehistoric Europe/ 



t In a paper " On the Obliquity of the Ecliptic," read before the Geo- 

 logical Society of Glasgow in 1807, I concluded that at the time of the 

 deposition of the Carse-clays the mean winter temperature was probably 

 10° or 15° lower than at present, and the Gulf-stream considerably re- 

 duced. See also ( Climate and Time,' pp. 403-410. 



