Ch. XIII.] THE INCLINED POSITIONS OF STRATA. 265 



their inclination than that of igneous elevation, to which such 

 phenomena have been referred in almost every instance. 

 But why make this exception ? Because it would be other- 

 wise necessary to imagine horizontal strata of pebbles many 

 miles in thickness. But why be daunted at the contempla- 

 tion of a single member of the tertiary group, only a few 

 miles in depth, after having viewed, unmoved, the supposed 

 elevation of not only the total mass of tertiary rocks, but 

 also of the whole series of secondary rocks, which, subjected 

 to the same measurement, would indicate an incomparably 

 greater thickness ? Yet these are, in every portion of the 

 globe, found resting on each other in an inclined position, 

 for very many leagues from the mountainous ridges of 

 granite : and, surely, if it be no easy matter to conceive 

 strata of tertiary gravel, less than nine miles in thickness, it 

 must require a much greater scope of the fancy to conceive 

 such enormous masses of primary slates and secondary rocks 

 to have been elevated from a horizontal position by the pro- 

 trusion of granite. Some idea may be formed of the great 

 depths from which such horizontal strata must have been 

 raised, since Humboldt has observed a single rock, clay-slate, 

 dipping N.W., at an angle of 70, for forty-five successive 

 miles. We quote from Greenough's " Essay," who adds, 

 " Can it be imagined, that these strata were once horizontal, 

 and consequently fifteen leagues thick ; or that, falling, they 

 found a chasm large enough to receive them ? w * So Mac- 

 culloch says, " the thickness of the erected edges of a series 

 of strata, is the measure of the original depth before eleva- 

 tion : and it has been computed by Playfair, from observ- 

 ations of Pallas in the north of Europe, that we probably 

 by this means gain access to sixty-one miles in depth, or 

 nearly a sixty-fifth part of the radius of the globe." f But it 

 must, in fairness, be observed, that he thus concludes this 

 topic : " According to the rules above laid down for com- 



* Geological Essays, p. 53. f System of Geology, vol. i. p. 96. 



