GEOLOGY APPLIED TO CIVIL ENGINEERING. 113 



Geologist required, in proving that by interference with the 

 natural line of drainage (in other words, the dip of the 

 strata) in a manner to throw the surplus of water from the 

 surface soil, along a natural slope, into an exposed mass of 

 earth beneath, the engineer has disturbed the natural drain- 

 age which is beneath the several beds, in the direction above 

 referred to ; and fourthly, whether the intersection of the 

 strata has taken place in such a manner as to leave a portion 

 of earth unsupported, on the slope of the natural dip of the 

 strata, and hence facilitated its descent, however accurately 

 the mechanical laws for slopes in earth work have been 

 observed. These reasons will at once suggest the value of 

 Geological knowledge in the enquiry, and as in this instance 

 we hope to prove that the " slips^^ in question originated 

 from Geological causes, so to speak, that so on future occa- 

 sions, our work may be made the medium for similar enqui- 

 ries, and for preserving the records of the Geological 

 appearances on the various lines of railway in this country. 



On the Croydon Earth-slip. — ^The deep cutting in which 

 this slip occurred is formed in the London clay formation, 

 which is a portion of the great London basin, and possesses 

 a laminated structure in the direction of the line of depo- 

 sition ; although without apparent stratification. In Fig 1^ 



Fig. 1. 



VOL. T. NO. IV. ^ I 



