E.— GEOGRAPHY. 99 



whose seeds ripen as the ground dries, and lie dorniiint till moisturu 

 comes again; or tiiey may be bulbous and iuberous forms, having but 

 a short period of vegetative activity, l)ut jjossessing undei'groutul stems 

 capable of withstanding prolonged drought. The result is that man 

 did not require to clear land for crops, Nature periodically cleared it 

 for him. He had but to make the fairly obvious deduction that water 

 alone was necessary for the apparently barren soil to blossom like 

 the rose, and from all the choice of plants which the flooded ground 

 offered, to pick out those of some use to him, and learn to suppress 

 the rest. As has oiten been pointed out, he did not need to trouble 

 greatly about renewing the fertility of his lands, for the flood-water 

 did this for him. 



Sc soon as he had learnt the initial lessons of cultivation, he was 

 tied to the area normally flooded at certain seasons, or to which he could 

 lead the flood-water He intercalated his crops along one of Nature's 

 lines of weakness, in a transitional ai'ea which passed periodically 

 from one climatic zone to another, being, according to the seasons, 

 either a desert or fertile. Fixed in this fashion he could, and did, 

 adapt his mode of life to the natural conditions as precisely as ever 

 bird or insect became structurally fitted for life on an island. 



The bordering desert ensured isolation, and, continuing the island 

 metaphor, we may say that it represented the sea. Its effect was to 

 throw the whole energy of the community towards the centre, for the 

 periphery formed an area in which the characteristic mode of life could 

 not be practised. Similarly, it gave protection, for it is unsuited to 

 any save a highly specialised culture, which must have been of relatively 

 late origin. So far as it formed the boundaries of the incipient state, 

 therefore, the desert constituted a barrier preventing the ingress of 

 potential foes. In neither case, of course, was the desert rim complete, 

 and the conditions upstream varied in the two areas, and were, as has 

 been often pointed out, from the point of view of safety, on the whole 

 less favourable in the case of Babylonia than in that of Egypt. 



As to the third point, it is, I think, easy to show that while the 

 isolation of the areas was markedly conducive to the rise of civilisation 

 and to its growtlr up to a certain point, in the long run it became a 

 danger. In the first place, the contrast between the belt which could 

 be watered and that to which, with the means available, water could 

 not be carried, was exceedingly shai'p. There was little possibility of 

 a gradual spread into areas becoming slowly but progressively different, 

 where new aptitudes could be acquired, new experience gained, and 

 new forms of wealth stored. Specialisation was high within the 

 favoured tract, but the limits set by Nature could not be passed. 



Again, as has often been noted, the conditions led necessarily to 

 a centralised and imperialistic form of social organisation. If there 

 was a sharp line of demarcation between the areas which could and 

 could not be watered, there were great possibilities in the direction of 

 extending by artificial means the belt over which the flood-water spread. 

 This involved the gradual growtli of an elaborate irrigation system, and 

 for the maintenance of this a centralised power was essential. This 

 brought with it, as a correlated advantage, the possibility of organised 

 defence when developing neighboui'ing communities attempted to 



