. Calcutta journal of natural history, and miscellany of the arts and sciences in India. se localities by boring through thehard and massive rocks has naturally failed, and the failuresare easily explicable from the circumstances above stated. The alternations of porous with impervious strata in latersedementary deposits, and the continuity of these over ex-tensive areas, with their occurrence at high as well as lowlevels, furnish us with those dispositions which most favour 24 Economic Geology. the adoption of the Artesian system. The extensive develop-ment of secondary and tertiary formation
. Calcutta journal of natural history, and miscellany of the arts and sciences in India. se localities by boring through thehard and massive rocks has naturally failed, and the failuresare easily explicable from the circumstances above stated. The alternations of porous with impervious strata in latersedementary deposits, and the continuity of these over ex-tensive areas, with their occurrence at high as well as lowlevels, furnish us with those dispositions which most favour 24 Economic Geology. the adoption of the Artesian system. The extensive develop-ment of secondary and tertiary formations over the surfaceof the earth affords a wide field for boring operations, andalready in England, France, Germany, Italy, America, andit is said in China, they have been extensively and success-fully employed. To illustrate the geological principles onwhich the action of Artesian springs depends, let us supposethat the upper part of a hill, A, consists of a soft poroussandstone, and that by noting its dip, it is observed to passat a low angle, beneath the plain B; continuing the exa-. mination of the locality it is found that the sandstone iscompletely covered by a bed of close adhesive clay, overwhich again a certain depth of surface soil reposes. Nowwith this arrangement, which is not an uncommon one, it willreadily be observed, that the water falling on the sand-stone being easily absorbed by it will naturally seek thelower level of the plain, passing underneath clay, andas the process of absorption will have been in progress forages, it is probable that the water-bearing stratum willbe highly charged. Should it have become thoroughlysaturated, a series of natural Artesian springs will befound along the line of junction of the imperviousclay with the sandstone, and should this line be butlittle elevated above the level of the plain, it would beunadvisable to attempt boring, since the water would becarried off by these natural drains. But if no springs arefound, or if they ar
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