760 



SCIENCE 



[N. S. Vol. XX5C1I. No. 830 



letter entitled " Shackleton's Contribution to 

 Biogeography " was intended as suggestive 

 rather than positive. Such may be gathered 

 from the opening paragraph. But perhaps 

 some may conclude from it that I view Ant- 

 arctica as practically the only land connection 

 that has existed between the various conti- 

 nental masses, or between the eastern and 

 western hemispheres; that I consider that 

 faunal and floral elements have ever traveled 

 northward, and have reached the northern con- 

 tinents through the southern from Antarctica 

 as a center of dispersal. This is not the idea 

 that I wish to convey. There have been north- 

 ward and southward dispersals of types, and 

 eastward and westward dispersals as well. 

 There has certainly been land connection be- 

 tween Eurasia and North America in the 

 Bering region in times past, and many types 

 have passed over that bridge, some going one 

 way and some the other. There are distinct- 

 ively northern types that have spread south- 

 ward into the continents of the southern hemi- 

 sphere, but there are also southern types that 

 have spread northward. There is evidence for 

 believing that the southward dispersals are 

 much more recent than the northward, taken 

 as a whole. 



The biogeographical role which I conceive 

 Antarctica to have played is that of a center 

 of distribution of the earlier forms of life; 

 and later, perhaps, an exchange ground be- 

 tween the southern continents for old-type 

 stocks, many or some of which traveled north- 

 ward into the continents of the northern hemi- 

 sphere. The main point after establishing the 

 Antarctic contacts is to determine the length 

 of their duration with the southern continents. 

 It is quite possible that none of these contacts 

 persisted into Tertiary time, and my sugges- 

 tion that Africa may have been connected 

 with the southern mass until the Miocene is 

 perhaps wide of the mark. The distribution 

 of certain forms which prompted the sugges- 

 tion may have to be otherwise explained. It 

 was during Paleozoic and Mesozoic times that 

 I consider Antarctica to have been especially 

 active as a center of dispersal and exchange. 

 I should better have said in my former com- 



munication that during Mesozoic (Jurassic to 

 Cretaceous) times the continent was probably 

 not dissimilar to present-day South America 

 and Asia in average elevation; and that its 

 subsequent further uplifting, together with 

 the enormous weight at times of its ice-sheet, 

 which has repeatedly extended and decreased 

 in accordance with changing conditions of 

 altitude and temperature, caused its shelf lines 

 to sink beneath the ocean. Its complete isola- 

 tion may have been effected before the Ter- 

 tiary. On the other hand, some of its contacts 

 may have prevailed until the Oligocene. At 

 all events there seems evidence enough to indi- 

 cate that at one time it played an important 

 part in the dispersal of old-type forms. 

 Doubtless Antarctica is the most remotely an- 

 cient of the continents, as indicated by its 

 greatest average elevation. 



I am well aware that most European and 

 North American students consider the great 

 majority of distinctively Tertiary and later 

 types to have originated in the northern hemi- 

 sphere, and I may add that this is also my 

 opinion. But it is well knovni that, at the 

 beginning of the Tertiary, many types of the 

 higher insects were already in existence, some 

 of which have persisted with little change to 

 the present day. This must necessarily have 

 been the case, since we find their remains scat- 

 tered through Eocene, Oligocene and Miocene 

 deposits. While evolution has undovibtedly 

 been most active in the development of new 

 types in the northern hemisphere since early 

 Tertiary time, and the prevailing trend of 

 migration has consequently been to the south- 

 ward, there seems much evidence to indicate 

 that prior to that time the reverse was the 

 case in large part at least. 



I shall be glad to see an expression of views 

 on this subject from paleontologists who have 

 made especial studies of various phyla. 



Charles H. T. Townsend 

 ProEA, Peeu, 



September 27, 1910 



AMERICAN EDUCATION 



To THE Editor op Science: The criticisms 

 passed on American education by Mr. Gunn 



