112 



THE GEOLOGIST. 



observation of the sub-soil in cases where the harmony of 

 nature is required to be disturbed by the wants or frivohties 

 of mankind. 



We will treat each of these " slips,'^ as they are commonly 

 called, separately;, in order that the respective details may 

 not be confounded ; but previous to so doing, we w411 con- 

 sider the causes from which these effects originate, in order 

 to show the practicability of Geological reasoning in such 

 causes. The natural cause of a " slip^' may be : 



1 — The destruction of the general equilibrium of a mass 

 of earth, by the removal of any portion in such a manner, 

 that the quantity remaining, falls from its own weight — -being 

 unsupported. 



2. — The complete saturation of a mass of earth by cons- 

 tant rain or wet, whereby the equilibrium is destroyed, and 

 the effect may be traced to a gradual weakening of the soil 

 on which it rests, added to the weight attained by the por- 

 tions next the surface which receive the greatest share of 

 moisture. 



3. — The intersection of the strata of any district in such a 

 manner, as to interfere with the natural drainage, whereby 

 the above cause (No. 2) may have originated. 



4. — The like intersection as in the preceding case, inter- 

 fering with the equilibrium of those portions of earth left 

 exposed above or belov/ the dip of the strata. 



We will not offer any remarks on the first case, which 

 must be apparent to every person ; the second is determined 

 by local circumstances only, such as the nature and situation 

 of a particular stratum, whether it is the lowest point of 

 drainage of a district, and hence the greatest receptacle of 

 natural moisture, under which circumstances, it is clear that 

 if a cutting or embankment was made in that part, it would 

 be more lia1)le to slip than in any other situation of that 

 district ; in the third case, we find the knowledge of the 



