312 THEORY OF SPRINGS. 



contain will be liable, in periods of heavy rain, to be more or less com- 

 pletely washed out and carried otf by the water that trickles through 

 them. While, therefore, the establishment of drains on all soils may 

 adapt and ])repare them for further improvements, and may make them 

 more grateful for every labour or attention that may be bestowed upon 

 them — yet after drainage they must be more liberally dealt with than 

 before, if the increased fertility they at first exhibit is to be permanently 

 maintained or increased. 



§ 3. Of the theory of Springs. 



In the general drainage of the land a double object is sought to be at- 

 tained. In very rainy districts, the first wish of the farmer is to carry 

 off the surface water from his fields — but where less rain falls, that 

 which ascends from beneath in springs, attracts at least an equal share 

 of the husbandman's regard. In draining, with a view to the removal 

 of this latter source of llperfluous moisture, a knowledge of the true 

 theory of springs, as indicated by an examination of certain geological 

 phenomena, is of the greatest possible service to the practical man, in 

 pointing out the sources from which the water that injures his land pro- 

 ceeds, as well as the lines along which it may be most etiiciently and 

 most economically carried off". 



1°. The rain which falls on the surface of an extensive tract of country 

 partly escapes into the rivers, and partly sinks into the earth. This 

 latter portion descends through the covering of soil and other loose ma- 

 terials till it reaches the rocks on which they rest. If these rocks are 

 porous, like many sand-stones, or are traversed by cracks and vertical 

 fissures, as many sand-stones and lime-stones are, it descends through 

 them also till it reaches a bed, such as one of indurated clay, so close and 

 compact as to resist its further passage. By this impervious bed the wa- 

 ter is arrested, and is, therefore, compelled to spread itself laterally, and 

 gradually to accumulate in the beds that lie above it. Thus, if the 



outline from A to C in the annexed diagram represent the surface of an 

 undulating country, « which the subjacent rocks (1, 2, 3, 4) are covered 

 by a considerable thickness of loose materials, the rain which falls from 

 A to B will sink more or less rapidly to the bed (1), and, if this be im- 

 l)ermoable to water, will rest there, or will slowly drain off' in the di- 

 rection of B and C along the inclined surface of the rock. But if (1) 

 be porous, it will sink through it to the surface of the bed (2), and 

 through this also, if permeable, to (3) or (4), until it reaches the stratum 

 through which it cannot pass. On the surface of this latter bed, or 

 among the rocks above it, the water will accumulate until, flowing 

 downwards towards C, it is enabled either to sink among the deeper 

 rocks or to make its escape again to the surface. 



But if the rocks beneath, as is shown in the same diagram from E to 

 F, be traversed by vertical fissures passing through two or more, or, like 

 the one represented from B to E, through a great number of beds, tha 



