BOOK II.

THEORY AND PRACTICE OE ENGINEERING.

CHAPTER I.

GEOLOGY.

Geology and Mineralogy are equally important to the civil engineer, and it is in proportionto his acquaintance with these comparatively modern sciences, that he is rendered skilful inthe formation of roads, canals, harbours, mining operations, building of bridges, or formingfoundations of any kind, and draining ; wherever the scene of his labours may lie, he cannotbe entirely successful, without a careful consideration of the various layers or strata com-posing the earth’s crust.

When Smeaton was called upon to construct the Eddystonc lighthouse, he commencedby examining the structure of the rock on which it was to be based ; and as far as waspossible endeavoured to imitate nature in his arrangement of the first and subsequentcourses. Had the builders of the Leaning 'lower at Pisa been equally careful, or had theybeen acquainted with the composition of the earth on which they laid their foundations, theworld would never have had the opportunity of supposing that its inclination was the effectof design, instead of the consequence of an insecure base, which might have been con-solidated by art; had the alluvial matter on which the footings are laid been convertedinto a mass of conglomerate or artificial rock, this famed Campanile would have stood asupright as the Eddystone lighthouse , a position which would certainly have been more inunison with the beauty of its architecture, though perhaps not so conducive to its celebrity.For all the purposes of building, it is necessary that the constructor should be acquaintedwith life formation and properties of the matter with which he has to deal ; he shouldunderstand the cause of the durability of a substance, whatever it may be, as well as whatdisintegrates or destroys it.

On examining the geological structure of England, we shall find that it exhibits nearlyall the variety of strata discoverable on the continent of Europe, in the same successiveorder ; the dip, though occasionally broken, generally inclines towards the east or south-east, and in this direction is the drainage effected. It is possible that before the rocks,which make up the greater portion of our island, were deposited, the general outlinewas marked out or defined on the bed of the ocean, and this platform, after having beenelevated by some disturbing forces, and the protrusion of igneous rocks, then received theseveral deposits, the succession of which with the variety of plants and animals of extinctgenera, the disturbance of the several strata after their formation, sometimes by theirelevation, at others by their depression, afford ample subject for consideration and en-quiry ; and from the talent and ability of the various geologists, who are giving free scopeto their researches, and diligently observing all that is opened to their view in the severalmilling districts, or where any deep cutting is made, we may hope in time to obtain a clearand satisfactory solution of those phenomena which are at present involved in doubt andobscurity. ,

In travelling through a country the geologist knows by the strike of a stratum, or seriesof strata, in a range of hills, with a steep fall on one side, and a gradual rising on the other,that the latter indicates the dip ; the prevailing strike being generally found to extend overthe whole tract of country ; and as by the inclination of the strata the drainage of the districtis effected, so the various rivulets may be accounted for, and their sources ascertained.

To the miner an acquaintance with geology seems indispensible, to enable him to tracethe various disruptured strata, which often baffle the observations of others. A correctestimate of the mineral veins, and the circumstances under which they have been formed, aswell as their general direction, can only be ascertained by a study of this science, and apractical acquaintance with the various rocks in which they abound ; but the mechanicalcontrivances by which the miner is to test his theories, and make them profitable, are pro-vided by the civil engineer : both private and public interest, therefore, demand that heshould be acquainted with these subjects, for if not conversant with the matter to be workedupon, it is scarcely possible that he should apply the proper means, certainly not with therequisite economy. On the coal fields, which are a most important study, we have scarcelyany thing written that is practically useful, although the subject of ventilation, and the pre-vention of accidents in mines, has obtained much consideration