Deserts 119 



comes in contact. The moisture has no chance of 

 condensing into a cloud, or rain, as it might if it 

 met with cool air, but is dispersed — drunk up and 

 evaporated by the hot, thirsty air from below. No 

 wonder, therefore, that the Sahara is a rainless region. 



The island of St. Helena, again, is a notable instance 

 of what man can do in the way of reducing a luxuriant 

 garden to a barren waste, simply by his ignorant or 

 reckless destruction of its natural vegetation. When 

 first discovered, the island, though very mountainous 

 and bounded by tremendous precipices rising some two 

 or three thousand feet above the sea, was very fertile, 

 and possessed a luxuriant growth of forest. For it is 

 astonishing what a thin film of soil is enough for seeds 

 to sprout in, if only it be moist ; and it is astonishing, 

 too, how little soil will suffice even for hardy evergreens, 

 birches, and other small trees, whose roots often grow 

 in immediate contact with the rock. But one thing is 

 absolutely necessary. If the soil be shallow, moisture 

 must be abundant. 



The soil of St. Helena was rich, being formed by the 

 slow decay of volcanic rocks, but it was not deep, and 

 was only kept in place by the roots which held it fast. 

 The Portuguese brought goats to the island, and by 

 these destructive animals the luxuriant vegetation was 

 in great part destroyed, for they multiplied by 

 thousands. There was a wanton waste of wood, too, 

 on the part of the human inhabitants, though some 

 were far-sighted enough to predict that the island 

 would be ruined when the * Great Wood ' was 

 destroyed. And so, sure enough, it was. 



Gradually the soil became more and more exposed, 

 and whenever this was the case, it was washed away 



