4 
THE ARTESIAN WELLS OF COLORADO, 
spread throughout Europe. They were, however, known 
and sunk in other countries centuries before, and some¬ 
times of extreme depth. 
The cause of the water rising to the surface and 
flowing, is an illustration of the familiar tendency of 
water to seek its own level. If the source of the water is 
higher than the surface of the ground where it is set free, 
the water rises with a force depending on the height of 
the source above that point, other things being equal. 
Whether a well flows or not will then depend on whether 
the mouth of the well is below or above the source. In 
many regions, where the ground gradually rises, there is 
an area outside of which the wells do not flow, because 
the surface is too high. Examples may be found where 
the water rises almost to the surface, and where the low¬ 
ering of the surface a single foot, as by digging a trench, 
would render it a flowing well. There is evidently no 
essential difference between the two cases, but according 
to the ordinary usage one is artesian while the other is 
not. In both wells the water rises above the stratum 
where encountered. This characteristic was taken as 
the basis of the meaning of the word as used by the 
U. S. Artesian Wells Investigation of 1890. To make a 
distinction between the two classes, which is practically 
important, it has been proposed to distinguish them as 
positive artesian, or simply artesian, and negative arte- 
sion—the former indicating those which flow. 
The conditions for the existence of an artesian well 
basin are, that there should be some source of water sup¬ 
ply higher than the location of the well, and that there 
should be a porous stratum which is confined by im¬ 
pervious strata both above and below. These strata must 
be continuous. In general, the water should have no 
means of escape lower than the point where the well is, 
but when the distance to an outlet is considerable, the 
