366 



EMBANKMENTS. 



Steeper slope than three feet horizontal for one foot 

 perpendicular. In cuttings in chalk or chalk-marl, 

 the slopes will stand at one to one. In sandstone, 

 if it be solid, hard, and uniform, the slopes will 

 stand at a quarter to one, or nearly perpendicular. 

 If a sandstone stratum alternates with one of clay 

 or marl, it is difficult to say at what rate of inclina- 

 tion the slopes will stand ; this will, in fact, depend 

 upon the inclination of the strata. If the line of 

 the road is parallel to the line of the bearing of the 

 strata, in such cases large masses of the stone be- 

 come detached and slip down over the smooth and 

 glossy surface of the subjacent bed. There are 

 many instances of slips in sandstone and marl stra- 

 ta, under such circu instances as those now descri- 

 bed, where the slopes are as much as four to one. 

 If the road is across such strata, or at right angles 

 to the line of bearing, the slopes may be made 

 one and a half to one ; but if the strata are hori- 

 zontal, even should there be thin layers of mar] 

 between the beds of stone, the slopes will stand at 

 a quarter to one. But it will be necessary, if the 

 beds of marl exceed twelve inches in thickness, to 

 face them with stone. In the Oxford clay, which 

 covers so great a portion of the middle counties 

 of England, the slopes should not be less, in any 

 instance, than two to one, and even in some parts 

 of this formation they should be made three to one 

 if the cuttings are deep. In all such cases, if any 

 beds of gravel or sand are found intermixed with 

 the clay, drains should be cut along the top, and 

 even in the sides of the cuttings ; for if this precau- 

 tion be not taken, the water, which will find its 

 "way into the gravel, will, by its hydrostatic pres- 

 sure, force the body of clay down before it, and 

 slips v^^ill take place even when the inclinations 

 are as much as four to one ; and, when this occurs, 

 it is extremely difficult to re-establish them. In 

 limestone strata, if solid, slopes will stand at a 



