754 



SCIENCE. 



[N. S. Vol. XIV. No. 359. 



to occur just as if no water were en- 

 tering anywhere else, and, therefore, the 

 systems of flowage to be superimposed. Of 

 course this is not a real case. Underground 

 water does not diverge from a single point 

 and converge at another point in independ- 

 ence of the water entering at other points. 

 The water entering at innumerable points 

 in vertical section and in horizontal section 

 mutually interferes, and makes the course 

 for any given particle of water rather 

 simple. This I have tried to represent by 

 another chart (Fig. 5). In this chart I 



Fig. 5. 



have supposed particles of water to enter 

 at equal horizontal intervals, and issue at 

 a single point. You note that the water 

 near the crest begins its journey by almost 

 vertical descent. In proportion as the en- 

 tering water is near the valley the hori- 

 zontal component becomes more important. 

 The water near the valley follows a com- 

 paratively shallow course; but this water 

 uses all the available space near the sur- 

 face, and consequently the water entering 

 at the higher ground necessarily follows a 

 long, circuitous and deep course. The 

 chart (Fig. 5), therefore, represents the 

 flowage with many points of entrance and 



a single point of exit, where there is inter- 

 ference of the circulating waters. 



A portion of the water follows an approx- 

 imately direct path ; a portion of it less 

 direct paths ; and a portion of it a very 

 roundabout path. That is, the underground 

 water, following the lines of least resistance, 

 takes not only the direct passages, but also 

 the indirect passages. The lines in the 

 more direct path are closer together, and 

 the indirect path farther apart. These 

 facts have been ascertained by experiment 

 and by mathematical analysis. But every, 

 where gravitative stress is the driving force. 

 The case represented by the diagram (Fig. 

 5) is an ideal one. Under the complex 

 conditions of nature there is usually great 

 departure from the simplicity represented ; 

 but in some districts this ideal simplicity 

 must have been approached. For instance, 

 except for the disturbance due to cutting 

 dikes, the circulation in the past in the San 

 Juan district of Colorado mast have been 

 very nearly like that represented in the 

 diagram. Early in Tertiary time there was 

 in that district a great volcanic plateau. 

 Early in the erosion history of this plateau, 

 the conditions must have been the same as 

 at present in the Yellowstone Park and 

 other volcanic plateaus of the West. At 

 the stage when the San Juan plateau was 

 still the dominating topographic feature, 

 but cut by canyons, the conditions were 

 practically identical with the conditions 

 represented by the diagram. The water 

 sank into the ground upon the hills aind the 

 plateau ; it issued at the valleys, much of 

 it having first penetrated far below the level 

 at which it issued. The water carried on 

 its search for metals through the volcanics, 

 almost as shown in the diagram, except in 

 so far as it was influenced by larger cracks 

 or crevices, or by cutting dikes, or by im- 

 pervious layers. 



The principles illustrated by these dia- 

 grams show it is not necessary that 



