CHAP. IX.] LIMITS AND FEATURES. 309 



Sonoran region in America, and of the Ethiopian and Oriental 

 regions in the Old World. The whole area is extra-tropical ; and, 

 as Dr Heilprin remarks, " no other region can compare with the 

 Holarctic in the manifold variety of its physical characteristics. 

 Every form of terrestrial configuration, or condition of soil and 

 climate that may be represented in any other region, is also repre- 

 sented here, and on an imposing scale. From the ice-bound fields 

 of the far north to the burning desert-wastes of Turkestan on the 

 south, and from the deep forest-grown lowlands to mountain- 

 summits soaring thousands of feet above the level of perpetual 

 snow, we pass through all those various gradations of climate 

 which respectively characterise the Frigid, Temperate, and Torrid 

 zones. Densely covered forest-tracts, supporting, as in the north, 

 a sombre growth of pine and other coniferous trees, or, as in the 

 south, a vegetation of almost tropical luxuriance, alternate with 

 broadly open grass or pasture lands (tundras of Siberia, American 

 prairies and plains), which in some cases support over enormous 

 areas only a very scanty vegetation, and in others display a profuse 

 variety of vegetable productions. It is in this region that, in 

 addition to a most bountiful development of desert tracts, we meet 

 with the most elevated table-land (the Central Asian), and, at the 

 same time, with the greatest expanse of lowland on the surface of 

 the globe, the great plain of Siberia and north-eastern Europe." 



Although the essential unity of the greater portion of the 

 Nearctic and Palaearctic regions has long been fully recognised by 

 the American zoologists, several attempts to bolster up the alleged 

 distinctness of these artificial divisions have recently been made in 

 England 1 , one proposal being to recognise an Arctic or Boreal 

 circumpolar province cut off from both areas, although this is 

 practically begging the whole question. 



If I rightly understand his view, Dr C. H. Merriam 2 , who is 

 an ardent advocate for the zoological unity of the more northern 

 portions of both hemispheres, would distinguish a Boreal circum- 

 polar region common to both hemispheres ; while in America he 

 recognises south of this a Transition region, followed still more to 

 the south by the Sonoran. In the Old World he would have an 



1 Appendix, Nos. 28 and 35. 



2 Ibid. No. 19, pp. 24, 63. 



