PREFERENTIAL USE OF LARGER CHANNELS. 581 



This conclusion is based on the following facts: Openings in rocks are 

 never of uniform size. It has been seen that the resistance to how in 

 capillary openings is far greater than in supercapillaiy openings. In small 

 supercapillary openings the resistance is greater per unit of flow than in 

 larger ones. Thus there is a strong tendency for the water starting through 

 innumerable small openings to converge into larger and larger openings, 

 because these are the lines of least resistance. Of course, water may go 

 long distances underground without finding larger openings than those 

 near the surface, as in some sandstones; but if large openings exist, they 

 are fully utilized. Finally, when a single opening or a group of openings 

 larger than the average reach the surface at a lower altitude than the 

 average level of entrance of the water, there is a spring. 



This reasoning is confirmed by experimental work of King, who finds 

 that the flow in the Amherst sandstone of Wisconsin is faster along than 

 across the bedding planes. The openings along the bedding planes are 

 larger than those between the grains. The first are largely utilized in 

 flowage along bedding and the second must be utilized in flowage across 

 bedding planes." 



From his experimental work King holds "that the movements of 

 ground water across long distances must take place in considerable 

 measure through passageways larger than those which depend upon the 

 pore space fixed by the diameters of the grains which constitute the beds 

 themselves." l 



While I believe that in proportion as openings are large they are 

 much more fully utilized than a similar area of distributed openings of 

 small size, we must remember that the movement of the widely dispersed 

 deep water is often excessively slow, and that under these circumstances 

 the resistance in the capillary tubes per unit distance is reduced to a very 

 small, almost an infinitesimal, amount. (See pp. 141-142.) Therefore 

 capillary openings between the grains in the cases of great sandstone and 

 similar formations may be the chief channels of circulation for large quan- 

 tities of water and for long distances. That such openings are the chief 

 channels through which the water actually flows in the deeply buried sand- 

 stones bearing artesian waters is indicated by the fact brought out by 



«King, F. H., Principles and conditions of the movement of ground water: Nineteenth Ann. 

 Rept. IT. S. Geol. Survey, pt. 2, 1899, p. 126. 

 ''King, cit., p. 249. 



