156 DISTRIBUTION AND HABITS OF ARGALI SHEEP 



grazing grounds each one within its margin of desiccated 

 territory. 



But also these large isolated steppes became smaller 

 and the distance between them increased by the growth of 

 sterile sand-belts. 



Possibly there began even now at this early stage a 

 certain tendency to race -individuality caused by the isolation. 



Later, when these smaller steppes became still more 

 barren and poor in grass, the wild sheep retired along the 

 water courses up towards the nearest mountains, at the 

 margin of the desiccating steppe. 



But even these marginal regions became drier and drier 

 still and possibly more insecure (with the advance of man) 

 and the real mountains then became their ultimate refuge. 



The herds of each section of the steppe thus wandered 

 into the hills, the northern ones to the north mountains and 

 so on. Here the broad valley containing the water courses 

 became their highways and where no difficult topography 

 stood in their way they spread further along or in the ranges 

 until they found suitable territory. 



But even these mountain groups became or were 

 already in many cases isolated from each other through 

 desert formation or through original obstacles such as 

 glacier-filled valleys or belts of country, barren or poor in 

 vegetation. Consequently we may assume that the race- 

 difference, already begun through the isolation on the 

 steppes, was maintained or even more accentuated, until 

 we find it now such as it is. 



Except desiccation and such climatogical circum- 

 stances there are undoubtedly other causes to be taken into 

 account, in dealing with the present distribution of the wild 

 sheep. The invasion of agriculturists in the marginal 

 districts of the desert or the use of these regions for rearing 

 domestic cattle must have resulted in making the sheep 

 retire to the more unapproachable valleys in the interior of 

 the ranges. 



With regard to the western districts the probably very 

 early cultivation of the western part of the Tarim Basin resulted 

 in driving certain flocks of wild sheep right up in the high 

 plateaux of the Pamir, others to the less elevated and less 

 distant Tian-Shan and Kuen-Lun. Eastwards in the north- 

 ern or southern marginal ranges of Gobi and Mongolia we 

 find them at lower altitudes, probably because cultivation 

 began at a later date. 



Additional evidence that the wild sheep were originally 

 inhabitants of the plains can be adduced from many 



