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VoL, XIX, Second Series. 



ROCHESTER, N. Y., FEBRUARY, 1858. 



No. 2. 



NATUEAL AlfD ARTIFICIAI DRAINAGE. 



In the practical operations of underdraining, it 

 is important to Lave a correct knowledge of the 

 nature and sources of springs. 



The crust of the earth is composed of numerous 

 strata, or layers, lying one over the other, some of 

 which, such as gi'avel and sand, are highly porous 

 and absorbent, and readily permit the passage of 

 water ; while others, sucli as clay and some rocks, 

 are nearly, or altogether impervious. 



AVhen rain falls on a tract of country, part of it 

 flows over the surface, and makes its escape by the 

 numerous natural and artificial courses which may 

 e.xi^t; M'hile another portion is absorbed by the soil 

 and the porous strata which lie under it. 



L^t the following diagram (fig. 1) represent such 

 a tract of country, and let the dark portions repre- 



Fia. 1. 

 sent clay or other impervious strata, while the 

 lighter portions represent layers of gravel, sand, or 

 limestone, permitting a free passage to water. 



When rain falls in such a district, after sinking 

 throngli the surface layer (represented in the dia- 

 gram by a narrow band), it reaches the stratified 

 layers beneath. Through these it still further sinks, 

 if tliey are porous, until it reaches some impervi- 

 ous stratum which arrests its directly downward 

 course and compels it to find its way along its 

 upper surface. Thus, the rain which falls on the 

 space between B and D is compelled by the imper- 

 vious strata to flow toward ; here it is at once 

 absorbed, but is again immediately arrested by the 

 impervious layer E; it is, therefore, compelled to 

 pass through the porous stratum 0, along the sur- 

 face of E to A, where it pours forth in a stream, or 

 forms a swamp. 



Sometimes, in an undulating country, large tracts 

 may rest immediately upon some highly porous 

 stratum, as from B to C in the annexed diagram 

 (fig. 2), rendering the necessity for di-aining less 



"1 



Fig. 2. 



apparent ; while the country from A to B and from 

 C to D may be full of springs and swamps, arising 

 partly from the rain itself which falls in these latter 

 districts being unable to find a way of escape, and 

 partly from the natural drainage of the more porous 

 soils adjoining being discharged upon it. 



Sometimes the strata are disposed in the form 

 of a basin. In this ease, the water percolating 

 tlirough the more elevate ground collects in the 

 lower parts of the strata toward the center, there 

 forcing its way to the surface, if the upper imper- 

 vious beds be thin ; or, if otherwise, remaining a 

 concealed reservoir, ready to yield its supplies to 

 the shaft, or boring-rod of the well-sinker, and 

 sometimes forming a living fountain, capable of 

 rising many feet above the surfacfe. It is in this 

 way that Artesian wells are formed. The rakt which 



falls on such a tract of country at A and B (fig. 8"), 

 gradually percolates toward the center of the basin, 

 where it may be made to give rise to an Artesian 

 well, as at C, by boring through the superincum- 

 bent mass of clay ; or it may force itself to the sm*- 

 face through the tliinner part of the layer of clay^ 

 as at D, there forming a spring or swamp. 



