442 HYDROSTATIC PRESSURE EXEMPLIFIED IN SPRINGS, &C. 



dupoise of a cubic, foot of water ; and the final measure of effect he 

 therefore takes leave to express by 58,635,000,000 million Ibs. and 

 equal to the labour of 80,000,000 millions of men. Now the whole 

 population of the globe being reckoned at 800 millions, of which 

 only half, or less than that, is incapable of labour, it follows, that 

 the power exerted by Nature, in the mere formation of clouds, to 

 produce rain and make rivers and springs, exceeds by two hundred 

 thousand times the whole accumulated toil of mortals, who, if all 

 employed in carrying the water of the ocean to the mountain tops, 

 for streams, and watering the fields, meadows, and woods, could not 

 rival Nature in her simple process of evaporation, absorption, and 

 distribution. 



567. Such is the enormous power exerted in the great laboratory 

 of Nature above the earth. Let us now contemplate her exertions 

 beneath its crust, in the grand hydraulic apparatus of permeable 

 strata the casual introduction of faults and dislocations in imper- 

 vious strata, causing natural vents of water the interposition of 

 syphons, cavities, thermal springs, mineral waters all resulting from 

 the sea co-operating with the atmosphere to irrigate, to fertilize, to 

 bless the habitable earth. 



568. The surface of our own island contains 67,243 square miles, 

 which are watered annually by a pool of water about 36 inches deep, 

 of which, if one-sixth flow to the sea, there is still 2| feet depth left 

 to fertilize the land, to feed the permeable strata, and afford to each 

 individual the most abundant supply of this inestimable blessing. 



569. If a vertical section of Hertfordshire, Middlesex, Kent, and 

 Surrey, be taken, we shall have a pretty fair type of the sources of 

 Artesian or any other wells. Below the London clay we have plastic 

 clay, then chalk, then fire-stone, then gault clay, and below that 

 woborn sand. It is sufficient to bore through the tenderest plastic clay 

 into the chalk, to obtain the finest fresh water in the world. Kent and 

 Surrey abound in chalk, which dips deeply below the plastic clay 

 stratum, and makes its appearance at St. Alban's and Dunstable. 

 The woborn sand met with at Sevenoaks sinks below the fire-stone 

 and gault clay, and re-appears at Leighton Buzzard. Any one may 

 for himself sketch a perpendicular section of these districts, and a 

 few perpendiculars let fall through the London clay, to penetrate 

 into the chalk, by passing entirely through the plastic clay, will 

 exhibit the exact position of the borer in searching for water ; or the 

 reader will find it done to his hand in Dr. Buckland's Geology. 



