172 ON THE REVOLUTIONS 



viously formed. The action of a current, with the assistance 

 of the solid masses of every size transported by it, upon the 

 substance of any solid rock opposed to it, is subject to certain 

 laws, the principles of which must, in many respects, be com- 

 mon to it in the two cases just mentioned, as we shall have oc- 

 casion to point out more fully in the course of this paper. 



In attempting to apply these principles to the great scale of 

 geology, and to vindicate my opinions on this curious sub- 

 ject, I shall appeal to a series of facts which are very accessible 

 to this assembly, the greatest part of them lying within two or 

 three miles of this city. In that view, I have given, along with 

 this paper, a plan, on actual survey, taken on this account, of 

 a small district in the neighbourhood of Edinburgh, compre- 

 hending the Corstorphine Hill and its immediate neighbour- 

 hood. I thus hope to indicate the place of each specimen al- 

 luded to, in such a manner, that, provided the rock remains in 

 existence, it may be in the power of an observer to discover it 

 at any future period, however much it may have been con- 

 cealed by the accidents to which such specimens are perpe- 

 tually exposed. 



The country in the neighbourhood of Edinburgh is what all 

 are agreed to call Secondary, consisting of beds of sandstone, 

 and occasionally of limestone and coal, interstratified with 

 thick assemblages of shale, in loose and frail strata. This mass 

 is traversed with the utmost irregularity, by dikes or veins of 

 whinstone, which occur also in vast interjected masses, some- 

 times lying in great amorphous blocks, and sometimes in thick 

 beds, parallel to the strata. The strata, themselves, as might 

 be expected, are thrown, by means of its intrusion, into much 

 irregularity, and though nearly parallel to each other in any 

 particular spot, exhibit the utmost variety, when different places 

 are compared together, as to their dip and direction. This 



contrast 



