MUD. 139 



worms secrete an acid, which acts upon the bare surface 

 of rock beneath, and helps to disintegrate it in preparation 

 for plant life in unfavourable places. It is probable that 

 we owe almost more on the whole to these unknown but 

 conscientious and industrious annelids than even to those 

 ' mills of God ' the glaciers, of which the American poet 

 justly observes that though they grind slowly, yet they 

 grind exceedingly small. 



In the last resort, then, it is mainly on mud that the 

 life of humanity in all countries bases itself. Every 

 great plain is the alluvial deposit of a great river, 

 ultimately derived from a great mountain chain. The 

 substance consists as a rule of the debris of torrents, 

 which is often infertile, owing to its stoniness and its 

 purely mineral character ; but wherever it has lain long 

 enough to be covered by earth-worms with a deep black 

 layer of vegetable mould, there the resulting soil shows 

 the surprising fruitfulness one gets (for example) in 

 Lombardy, where twelve crops a year are sometimes 

 taken from the meadows. Everywhere and always 

 the amount and depth of the mud is the measure of 

 possible fertility ; and even where, as in the Great 

 American Desert, want of water converts alluvial plains 

 into arid stretches of sand-waste, the wilderness can be 

 made to blossom like the rose in a very few years by 

 artificial irrigation. The diversion of the Arkansas Eiver 

 has spread plenty over a vast sage scrub ; the finest 

 crops in the world are now raised over a tract of country 

 which was once the terror of the traveller across the 

 wild west of America. 



