in its beating on the Distribution 8^c. of Birds. 237 



presently endeavour to sliow, the stream of bird-life has been 

 continuous from the North Pole to the most southern regions 

 there is no evidence of life having been diffused from the 

 South Pole. There are only two forms of bird-life exclu- 

 sively circumpolar in the southern regions which have not 

 clearly a noi'thern origin^ viz. the Sheath-bills and the Pen- 

 guins. The former are too closely allied in structure to the 

 Oyster-catchers to enable us to found any argument on them ; 

 the latter may be the solitary survivors of a South-Polar 

 avifauna. 



But the physical conditions of the opposite zones are very 

 different. Sir J. Hooker has remarked that he can find no 

 plants in the Antarctic regions which do not bear indis- 

 putable traces of a northern origin^ except, possibly, a few 

 lichens and seaweeds. The results of the soundings of our 

 scientific expeditions show that almost the deepest sea- 

 bottoms on the face of the earth girdle the Antarctic conti- 

 nent, and Mr. Murray has pointed out that we have every 

 reason to believe that the deep ocean-depressions have existed 

 since the earliest solidification of the earth's crust. The 

 dredging of this ocean has produced no trace of sedimentary 

 rocks, but only the detritus of primitive or azoic rocks. Now 

 no spaces present greater obstacles to the transit of life than 

 deep oceans. We may infer, then, that, if bird- life did exist 

 on that primitive continent (and it very probably was created 

 there, as w'cll as at the north), when the temperature gra- 

 dually sank, mammals and birds could have had no escape 

 from the increasing cold, and, having no near lands in which 

 to take refuge, they, with the exception of the Penguin 

 family, ultimately perished. 



On one, and only one, hypothesis can the origin of life at 

 the Poles be controverted, and that is that the axis of the 

 earth may have changed, so that the Poles may formerly 

 have been at very different points of the earth's surface. But 

 our greatest mathematicians have examined this theory — first 

 started to explain the existence of the Miocene flora in the 

 Arctic zone — and Sir W.Thompson, Dr. Haughton, Prof. G. 

 Darwin, and others agree that there is no evidence of such 



