Water 



level 



FIG. 1 8. Relative size and storage ca- 

 pacity of dug and drilled wells. 



sand, gravel and boulders, deposited by glaciers. In texture it 

 varies from porous to impervious, according to whether sand or 

 clay predominates. It is, as a rule, not definitely bedded. The 

 water that it contains generally occurs in small more or less tubular 

 channels a few inches in diameter, but here and there is distributed 

 through interstratified sandy beds. 



In the aggregate, till yields a large amount of water, being the 

 prevailing source of supply in the rural districts at a great number 

 of points throughout the northern portion of the country. Be- 

 cause of the occurrence of the 

 water in definite channels, how- 

 ever, the success of wells in 

 till varies greatly. In general, 

 wells of large diameter give the 

 best success. Figure 18 repre- 

 sents two wells of the same 



depth, one dug and one bored. It will be seen that in the dug 

 well not only is a larger amount of material encountered in cross 

 section, but the area of surface from which water can enter is 

 many times greater than in the bored well. The open well is 

 also of larger storage capacity, and can be employed to utilize 

 small supplies supplies that would be insufficient 

 to furnish enough water to a bored well. 



Waters of Sandstones, Conglomerates and 

 Quartzites. Sandstone is, on the whole, the best 

 water bearer of the solid rocks. Under the most 

 favorable conditions sandstone is saturated through- 

 out its extent below the regular ground-water level, 

 and wherever it is struck by the drill within these 

 limits (see Fig. 19) it yields water freely, as a rule, 

 although some of the finer-grained sandstones yield 

 it less readily. In quality the water in sandstones 

 is, as a rule, better than that in any other material except sand 

 and gravel. Drilled wells are used to recover water from sand- 

 stone, except where it is very near the surface. 



FlG. 19. Ar- 

 rangement of 

 grains in sands 

 and sandstones 

 with interven- 

 ing pores open 

 and capable of 

 holding water. 



