OF THE EARTH'S SURFACE. 161 



plained. I trust, however, that the same principles will extri- 

 cate us from this difficulty also. 



If my view is correct, as to the violent manner in which our 

 continents have risen from the bottom of the sea, to their ut- 

 most elevation in the atmosphere, it is quite obvious, that the 

 cold and hard external crust, while it communicated such 

 shocks to the ocean, must itself have undergone the greatest 

 agitation, and must have been rent and broken in every con- 

 ceivable mode. The stone, in liquid fusion, introduced into 

 the rents, would assist the elevation, in so far as it tended to 

 facilitate the shifts, by enabling one mass to slide on the other ; 

 but forcing its way upwards, this liquid would at last reach a 

 temperature, in which, as we have said, it would congeal ; its 

 further progress in that direction, with respect to the neigh- 

 bouring substance, being thus effectually stopt, and the propel- 

 ling force from below continuing to act, the local elevation would 

 be converted into a more general one, either where the strata 

 were in a flexible state, by means of an horizontal thrust, pro- 

 ducing an elevation along with the convolution of the strata, 

 (in a manner lately pointed out in this Society), or, where the 

 neighbouring substances were inflexible, by a penetration of 

 the liquid through the mass, giving rise also to a vertical heave 

 of the whole. In either case, a number of rents would be 

 formed, in the hard outer crust, which would widen upwards 

 as the heave advanced *, thus forming the rudiments of valleys 



Vol. VII. X of 



* This elevation may be illustrated, by the familiar example of what happens 

 in the act of digging a piece of firm soil. The gardener first thrusts his spade into 

 the unbroken ground, then leaning on the handle, gradually forces the flat iron up- 

 wards ; by this means, a heave of the soil takes place ; the middle part being 

 raised, while the sides remain more or less attached to the firm soil. A separa- 

 tion between the two is the consequence ; and a formation of rents open upwardsc 

 which gradually become wider and wider as the spade rises. 



