When land abounds with springs, or is subject to the oozing out of subterraneous water, draining is effected in a different manner. Springs have their origin in the accumulation of rain water, which falling upon the earth, after passing the porous strata, lodges upon the impervious, and glides along the sloping surface until it crops out, generally in some valley where it forms a watercourse.
Descending streams are easily taken care of by collecting them into a body before they reach the low lands.
When a morass is to be drained, the strata upon which it reposes should be examined, and if, as is often the case, a layer of clay intervenes between the substratum and the mossy covering, which holds the water, by tapping this in well chosen places, the whole will sink away.
A fine example of embankment upon a bad bottom was performed by Mr. Stephenson, on the Great Western Railroad, England, at the crossing of Chatmoss. This moss was so soft that cattle could not walk upon it, and an iron bar sank into it by its own weight. The moss was first thoroughly drained by a system of longitudinal and cross drains, and the embankment made of the lightest material possible—the dried moss itself. Without this treatment, the moss would have sank beneath the bank alone; it now supports the passage of the heaviest railroad trains.
METHOD OF CONDUCTING OPERATIONS.
122. The organization of the engineer corps upon a railroad is as follows, differing somewhat in different parts of the country.
The Chief Engineer has entire charge of all the work, of all assistants, appointing and dismissing members of the corps, designing of all structures, making of specifications, and of all mechanical operations incident to the thorough, correct, and timely construction of the road; and should be able also to specify, generally, the amount and character of the equipment needed.
The Resident Engineer has charge of the detailed construction of from twenty-five to fifty miles of road, according to the nature of the work, being responsible to the chief engineer for the proper execution of the orders from headquarters; he returns to the chief engineer a monthly account of the exact condition of his work, both as to the amount executed, and also that remaining to be done.
The assistants of the resident engineer are a leveller and transit man; to whom, under his supervision, is the duty of laying out, measuring, and estimating the work. The leveller has with him one or more rodmen. The transit man, two chainmen, and one or more axemen.
In some cases, added to the above are inspectors of masonry, bridging, and superstructure. These are necessary only when the road embraces a great number of mechanical structures; too many to leave the proper time to the resident engineer for his other duties. Once each month the exact amount of graduation, bridging, and masonry executed is obtained by the resident and his assistants. The chief engineer applies the prices to these amounts, and the percentage deduction being made, the estimate is ready for the treasurer.