122 PHYSICAL SCIENCE BK. in 



fall of rock or earth, and the water being held back 

 seeks a fresh exit, which it forces with a certain 

 measure of violence ; or merely by the earth's vibra- 

 tion the course is shifted from one place to another. 

 On the surface of the earth one may observe that 

 rivers that have lost their channels are first of all 

 dammed back, but afterwards, in lieu of the course 



2 they have lost, force a new one. Theophrastus 

 affirms that an incident of the kind took place in the 

 Corycian Mount, 1 where, after a slight shock of earth- 

 quake, a fountain burst out from a fresh source. 



But some writers are of opinion that other causes 

 too are at work to call up water in other ways, or 

 to drive or turn it from its course. Mount Haemus 

 was once destitute of water ; but after a tribe of 

 the Gauls, being hard pressed by Cassander, took 

 refuge there, and felled the woods, an immense 

 supply of water appeared. No doubt the woods 

 had attracted it for their nourishment previously. 

 When they were uprooted, the moisture, ceasing to 



3 be used up by their roots, overflowed. Theo- 

 phrastus affirms that the same thing happened near 

 Magnesia. 



But with all respect to Theophrastus, this is not 

 a very likely story. Everything that is most shady 

 tends most to gather water. But that would not be 

 the case if trees drained off water. Roots draw their 

 nourishment from their immediate vicinity ; but the 

 volume of river water flows from recesses far down, 

 and is derived from a source deeper than roots can 

 penetrate. Besides, when trees are cut down, more 

 moisture than before is required ; the stumps suck 

 up a supply, not merely for life, but for new growth. 



4 Theophrastus tells us, too, that round Arcadia, 



1 In Cilicia. 



