ElylSHA MITCHELL SCIENTIFIC SOCIETY. 37 



SO that the water that falls upon this surface, instead 

 of running- off in opposite directions, if the soil is suffic- 

 iently porous naturalh' percolates downward and tends 

 to concentrate along- the lower portion of such basin or 

 valley where it may meet with least resistance in the 

 more porous materials. 



By way of exploring- such a reg-ion, a number of 

 holes are bored in line across the basin or valley, so as 

 to determine the existence and location of such an un- 

 derg-round "current" of water. In this way its posi- 

 tion at intervals is determined and the intervening- 

 course is traced by additional borings. If the water 

 supplv is tapped by these boring-s it sometimes over- 

 flows; the output of the pipe at the surface of the g-round 

 and the qtiantity thus overflowing- is measured, and 

 pumps are then applied so that the possible 3'ield of 

 water can be estimated. In these underg-round 'streams' 

 the water usually follows the topographic conditions, 

 as mig-ht be expected, but in some cases it moves more 

 or less obliquely across the ravines, showing- that the 

 overlying- soil has not the same thickness everywhere, 

 and that the topography of the soil surface is not the 

 same as the topography of the underlving rock surface; 

 and the water current moves along down the incline of 

 least resistance of the rock surface, in a measure inde- 

 pendently of the topography of the surface soil. 



The fact that that the water percolates through 

 this more or less porous material at considerable 

 depths below the surface, of course suggests that 

 the mo^'ement must be sluggish; but that there is a 

 definite movement is shown b}' the fact that where 

 there are a number of holes bored at intervals along 

 the line of the "stream" and coloring matters are in- 

 troduced into one of them, in a short time the color ap- 



