116 FLORIDA GEOLQGlCA.k, S.U^EY—J^IIRP. ANNUAL REPORT. 
amount.of water available is ljbpnited on the?one hand by The amount 
of rainfall upon the catchment area. and’^e Ia,oility : .with: which 
the rainfall can obtain entrance to. the, porous stratum* -and on the 
other band by the capacity of the water-bearing rock to transmit 
the water over long distances and diminution through leakage and 
seepage. These two limiting conditions are usually of sufficient 
magnitude to render the overdrawing, pf the/supply a practical 
and present danger which should be constantly kept in mind.’" 
r With regard to the artesian basin at Denver, Colorado, the 
•failure of which was unusually rapid, Slichter says: “This basin 
was discovered in 1884, and in a feW years about 406 wells had 
been drilled within an area extending a distance of 40 miles along 
South Platte River in a strip about 5 'miles wide oil both sides of 
the stream. Most of the wells were within the limits of the city 
itself. Many of the wells had a good pressure and strong flow 
when first constructed. In 1886 it was hot thought that any gen¬ 
eral decrease in the flow of the wells could be detected. Between 
1888 and 1890, however, a continuous decrease in the flow of the 
city wells took place, and by the end of the latter year all but six 
of the city wells had to be pumped, while nufnefous wells in the 
basin were permanently abandoned.” 
CAUSE OF THE LOSS OF FLOW. ; 
The loss of flow may be due to several causes/ it is frequent¬ 
ly the case that the life of an artesian well is limited. The escape 
of water through the well relieves the pressure which results in 
a reduced flow. In some instances pressure has so far been relieved 
that wells have ceased to flow entirely. This may be regarded 
as a natural and unavoidable loss of flow. 
The second cause of reduced flow which may have affected the 
Jacksonville and other wells is interference of wells. Numerous 
instances are on record where one artesian well has affected sur¬ 
rounding wells. 
A third possible cause is clogging of the wells through accum¬ 
ulation of sand or other material in the pipes or in the formations 
through which the water comes. In addition to the accumula¬ 
tion of sand it is not impossible that the porosity of the formation 
immediately around the well may have been more or less affected 
by chemical deposition since the well was drilled. It seems prob¬ 
able, however, that the clogging of the pores of the rock is more 
likely to be caused by material mechanically transported than by 
chemical deposition. 
Improper casing is likewise a frequent cause of failure. It is 
frequently the case that an insufficient length of casing is used in 
