Engineering Geology

e neighbourhood will yield, and this of course varies, both in quantity and quality, according to the nature of the rocks themselves. It may be assumed that the local quarries, lime-kilns, brick-yards, etc., will almost certainly be on the outcrop of beds most prolific in building materials, and afford good evidence of the kind required. But geological knowledge is nevertheless requisite to guide the engineer in laying out his works so that they may strike the more valuable strata to the best possible advantage. Building material is frequently brought long distances, when that which is as good, or even better, occurs in the vicinity?although perhaps hidden by a few feet of drift?it may be in abundance. A railway- cutting or a tunnel may be judiciously set out so as to follow exactly the course of a useful stratum, even toa considerable depth from the surface, probably to rail level. On the other hand, it may be planned so as to miss the bed, except just at the surface, or possibly altogether; for the point in question depends upon the direction of the dip of the stratum, its consequent strike, and the actual amount of its inclination. The drift gravels occur in a more irregular manner than any other series of deposits, but if they be previously mapped, and the work be designed accordingly, a great saving may be effected; the labour of excavating a cutting, for instance, may perhaps be made to yield the additional result of affording ballast or road- metal... --This text refers to an alternate Paperback edition.