This method involves the expense of moving the temporary roads, but allows more time for subsidence, and the mass of an embankment is not so exposed to the weather; however, in a dry season, an embankment can often be tipped to the full height, whereas in wet or changeable weather it would not stand if so deposited, and two lifts may be required. Care should be taken that the width is always sufficient to receive the top lift. It is more in the direction of equally reducing the height the material has to be tipped, especially in treacherous soils, that solidity is to be attained, than in an attempt to consolidate earth by endeavouring to cause it to fall together by deposition from two or more separate parallel roads at the same level. Many slips and failures of embankments have been caused by the central portion being deposited of one material, such as clay, and the slopes afterwards made of a different earth, as rock. The latter will then slip upon the greasy surface of the clay, the porous nature of the broken rock readily admitting water and air. In fact, a more flagrant example of effecting that which on no account should be done is not easy to imagine. In treacherous soil the system of tipping an embankment wider than that required from considerations of lateral and vertical settlement, and allowing it to stand at a steeper slope than its permanent angle of repose, and paring down the top unnecessary width is not to be commended, as the earth is then strained, and the lower portion is in the looser condition and the toe the weakest part: however, in the construction of a single line of railway with a narrow formation width, it is very convenient as affording room for roads for loaded and empty waggons, and in any soils other than aluminous and calcareous earths it may be done with impunity, provided all slimy and slippery surfaces are removed. No side tipping should be allowed in depositing a new embankment, and any addition of soil to a slope should be avoided as much as practicable, although in trimming some filling may be necessary, but the slopes should be rough trimmed by the bank-head men as the earth is deposited so as to prevent hollows and depressions, form a comparatively even and regular surface, cause the mass to be equally exposed to the weather, and prevent any lodgment of water. The form a tip head naturally assumes will afford some indication of the stability, for should it be regular and approach a semicircular shape it shows the earth is of a comparatively uniform character and is subsiding equally. When it is uneven and jagged, with streaks down the tip, it indicates unevenness of soil and condition.