Of the works mentioned, wells have fairly a primary claim upon the notice of the sanitary engineer, for, without undervaluing other sources of supply, the water from them certainly possesses the advantage over that from rivers and surface drainage, of being without organic admixture and unimpregnated with those deadly spores which find their way into surface waters and are so fatal in seasons of epidemic visitation. A great deal of the irregularity in the action of wells, and the consequent distrust with which they are regarded by many, is attributable either to improper situation or to the haphazard manner in which the search for underground water is frequently conducted. As regards the first cause, it cannot be too strongly stated that extreme caution is necessary in the choice of situations for wells, and that a sound geological knowledge of the country in which the attempt is to be made should precede any sinking or boring for this purpose, otherwise much useless expense may be incurred without a chance of success. Indeed, the power of indicating those points where wells may, in all probability, be successfully established, is one of the chief practical applications of geology to the useful purposes of life. Two cases in point are before me as I write; in the one 15,000_l._ has been spent in sinking a shaft and driving headings which yield but little water, found abundantly at the same depth in a mine adjoining; and in the other a town would be, but for its surface wells, entirely without water, the waterworks having been idle for weeks, and the sinkers are feebly endeavouring to obtain water by deep sinkings, in a position where its occurrence in any quantity is physically impossible. Ample supplies could be obtained in both these cases by shifting the situation a few hundred yards. The subject-matter of the following pages is divided into chapters which treat of geological considerations, the new red sandstone, well sinking, well boring, the American tube well, well boring at great depths, and examples of wells executed and of localities supplied respectively, with tables and miscellaneous information. Each system with its adjuncts has been kept complete in itself, instead of separating the various tools and appliances into classes, the plan adopted in the most approved French and German technical works. This, however, when too rigidly adhered to, as is the case with German works in particular, renders it troublesome for even a practised engineer to grasp a strange system in its entirety, while the pupil is wearied and retarded in his reading by an over-elaborate classification.