344 DESERT SANDS 



There, ranges of high mountains extend almost all round 

 the coasts, and so completely intercept the rainfall which 

 ought to fertilise the great central plain that the rivers are 

 almost all short and local, and one thirsty waste spreads 

 for miles and miles together over the whole unexplored 

 interior of the continent. 



But why are deserts rocky and sandy ? Why aren't 

 they covered, like the rest of the world, with earth, soil, 

 mould, or dust ? One can see plainly enough why there 

 should be little or no vegetation where no rain falls, but 

 one can't see quite so easily why there should be only sand 

 and rock instead of arid clay-field. 



Well, the answer is that without vegetation there is no 

 such thing as soil on earth anywhere. The top layer of the 

 land in all ordinary and well-behaved countries is composed 

 entirely of vegetable mould, the decaying remains of in- 

 numerable generations of weeds and grasses. Earth to 

 earth is ti}G rule of nature. Soil, in fact, consists entirely 

 of dead leaves. And where there are no leaves to die and 

 decay, there can be no mould or soil to speak of. Darwin 

 showed, indeed, in his last great book, that we owe the 

 whole earthy covering of our hills and plains almost 

 entirely to the perennial exertions of that friend of the 

 farmers, the harmless, necessary earthworm. Year after 

 year the silent worker is busy every night pulling down 

 leaves through his tunnelled burrow into his underground 

 nest, and there converting them by means of his castings 

 into the black mould which produces, in the end, for 

 lordly man, all his cultivable fields and pasture-lands and 

 meadows. Where there are no leaves and no earth-worms, 

 therefore, there can be no soil ; and under those circum- 

 stances we get what we familiarly k^ow as a desert. 



The normal course of events where new land rises 

 above the sea is something like this, as oceanic isles have 



