10 
VORKSHIKK NATl llAMSTs' UNION. 
This unifoniiity of (lis})ersal fruin the evolutionary centre is, 
however, in Nature hindeied by physical and other barriers, and, 
therefore, tends to follow certain definite paths which have through- 
out recent geological times V)een obviously determined by the direction 
and character of the great mountain chains, which in Europe and Asia 
are disposed chiefly in a latitudinal or horizontal direction, or from east 
to west, while on the American continent the direction is diametrically 
different, tlie great mountain ranges running longitudinally or from 
north to south. 
Ki(j. 4. — Map illustrating the positions, general arrangement and directions of the great 
mountain ranges of the world, to show their influence in determining and defining the paths 
of life dispersal from Europe. 
In Europe, the Pyrenees, the Alps, the Carpathians and other 
mountain ranges more or less effectually liinder or limit diffusion to 
the Mediterranean region and beyond, while the deserts and bleak 
and lofty table-lands of Central Asia offer almost impassable barriers, 
so that the easterly migrants by the northern route are comj)elled to 
traverse Russia, by a route passing through the South Central 
Provinces and entering Asia to the south of the Tral Mountains, and 
to continue their march along the comparatively fertile tract to the 
north of tlie inhospitable montane and desert region. 
On reaching the Pacific Ocean the migrants diverge, a ])ortion 
turning north and crossing by a formerly e.xistent Aleutian land- 
l>ridge to North America, while the remainder turn southward, 
])assing through China and giving off a contingent which enters India, 
while the larger number enter Siam and neighbouring countries and 
spread over the e([natorial Malayan islands, Australasia, etc. 
The section which crossed to North America dispersed towards 
the south, this direction being necessitated by the longitudinal 
direction of the great mountain ranges, the migrants eventually 
reaching and traversing Central America and })enetrating into and 
