1020 



HISTOmCAL GEOLOGY. 



EPEIROGENIC CHANGES DURING THE QUATERNARY. 



The upward continental movements of the early Quaternary and the late 

 Tertiary, by which the greater mountain regions of the globe were elevated 

 from 10,000 to more than 20,000 feet, and, following this, the wide-reaching 

 but feeble downward movement of the Middle Quaternary, and then the more 

 limited elevation closing the Champlain period, and, last, the settling back 

 of the land to the degree of equilibrium characterizing Kecent time, brought 

 gradually and grandly to an end the earth's mountain-making. The move- 

 ments were epeirogenic, and involved the whole sphere. It has been thought 

 incredible that the orographic climax should have come so near the end of 

 geological time, instead of in an early age, when the crust had a plastic layer 

 beneath, and was free to move ; yet the fact is beyond question. The event 

 is made, on cage 392, a legitimate effect of lateral pressure in the contracting 

 crust ; and the coral-island subsidence, or, in more general language, the 

 deepening of great areas over the oceanic basin, is set forth on the same 

 page as the counterpart. 



Why, in the upward movement, the colder latitudes, or those outside of 

 the parallel of 40°, should have been most affected, as the distribution of 

 fiords and other facts make evident, is wholly unexplained. The interest 

 of the problem is greatly enhanced by the new facts proving that the Ant- 

 arctic Continent also was elevated and greatly enlarged, — probably to four 

 times its present area; that not only the lands of the high northern lati- 

 tudes were affected, but also their antipodes in the high southern latitudes. 

 Under these conditions the earth's polar diameter would have received a 

 considerable increase of length, and the waters would have been deepened 

 over the lower latitudes. 



The idea of Croll, that the Glacial periods of the northern and southern 

 hemispheres followed one another, has no support from geological facts, and 

 few supporters among geologists. 



The Champlain subsidence following the elevation has been attributed, 

 on the principle of isostasy, as stated on page 379, to the weight of the 

 load of ice over the glaciated land. The cause is good in principle, but 

 of doubtful sufficiency. The facts stated on page 980, with regard to the 

 departure of the ice from the United States before the subsidence had made 

 much progress, indicate a great lagging in the effect, far greater than is com- 

 patible with the results of a load. Moreover, the coast region of California 

 subsided deeply (page 985) although it had not been covered by ice ; and 

 the land which joined South America with Cuba and probably Florida, and 

 that uniting Africa to Malta and Sicily disappeared, although far outside 

 of the ice-limit. The dry land across the British Channel between England 

 and France continued emerged long after the mild climate, which favored 

 migration of warm climate Mammals, set in ; and it became submerged 

 although the land either side was never under the ice-sheet. France and 



