Letters, Announcements, S^c. 527 



The Glacial epoch was comprised in the Pleistocene, with 

 which it may be regarded as practically equivalent. 



Most of the birds' bones which have been found in cave- 

 breccias and other Pleistocene deposits appear to have been 

 those of species that are still living at the present day ; and 

 there is no reason to believe that changes in birds have taken 

 place more rapidly than in Mammalia, the fossil remains of 

 which are far more abundant. Indeed the evidence points 

 rather the other way. Now the majority of the Pleistocene 

 Mammalia are living species and, so far as it is practicable to 

 judge, nearly all — perhaps all truly generic forms, such as 

 are adopted amongst birds by Mr. Seebohra — date from the 

 Pliocene at least, whilst many are older. 



In cases such as those of Scolopax and Cursorius, where 

 the differentiation suggested only extends to a few allied 

 species, there is a greater possibility that Mr. Seebohm may 

 be correct. Indeed some years ago I suggested a similar 

 origin — the intervention of an ice-covered continent in the 

 Glacial epoch — to account for the separation of certain allied 

 species of migratory birds in Eastern and Western Asia ; 

 but the hypothesis should be used with caution. I doubt 

 whether, in any case, all the species of any considerable 

 genus have been differentiated since the commencement of 

 the Pleistocene. 



Mr. Seebohm's geological views are also, I think, in several 

 respects open to exception. It is possible that there may 

 have been half a dozen alternations of glacial and interglacial 

 phases in the Pleistocene epoch (p. 226), but it is at least 

 equally probable there were none ; and certainly the evidence 

 existing for more than one interglacial phase is quite insuffi- 

 cient to justify the founding of arguments upon it. Then 

 what reason is there for supposing that at one portion of the 

 Glacial epoch a glacier (ice-sheet?) stretched '^from the North 

 Pole down the mountains of Greenland'' (p. 226), and that 

 in a subsequent phase of that epoch a different glacier ex- 

 tended '' across the North Pole from the Rocky Mountains 

 either to Novaya Zemlya or to the mountains of Eastern 

 Siberia"? (p. 227). Unless a change in the distribution of 



