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CHAPTER IV. 



DUST-MAKERS AND DUST-CARRIERS RUNNING WATER. 



Running Water : the Tools with which it Works The. Colorado and its 

 Canons Loads, seen and unseen, transported by Rivers Caverns 

 in Limestone Rocks. 



SOMETHING more than three-fifths of the rain which 

 falls over England and Wales sinks into the ground 

 and goes to feed the springs, from which, in dry weather, 

 except in the neighbourhood of snow-clad mountains, all 

 brooks, streams, and rivers, derive their whole supply 01 

 water. And as these increase in volume the farther they 

 flow, it is evident that they must receive supplies, not only 

 at their source, but at various points along their course. The 

 river Churn, for instance, starts with a flow of eleven cubic 

 feet of water per minute ; but a quarter of a mile from the 

 spring head, though it has not been joined by any visible 

 tributary streams, the flow has increased to thirty-one cubic 

 feet, and at a distance of five miles and a half it has in- 

 creased again to 320 cubic feet, so that other and perhaps 

 many small springs must have discharged themselves in- 

 to it. 



Now all running water, whether it flows above or below 

 ground, has some power of wearing away its channel. Flowing 

 at the rate of but three inches a second, it will tear up 

 fine clay ; at double this speed it will remove fine sand ; at 

 twelve inches it will sweep away fine gravel, and at three 



