190 THE PAST AXD FCTURE OF GEOLOGY. 



otberaiul smaller portions of the crust, presenting less resistance, yielded, 

 and rose at right angles to the tangential pressure. 



Now either, if the elevatory force were limited and uniform iu de- 

 gree, a point would be reached at which that force was balanced by 

 the increasing resistance and weight of the strata, and the movement 

 would cease; or else, if the energy was a constantly-generated quantity, 

 and the rigidity such as to prevent yielding beyond a certain extent, 

 (and no solid crust can be perfectly flexible,) then it would be a dy- 

 namical necessity that a time would come when, from the accumulation 

 of that energy, it would overcome the resistance, and the opposing 

 strata be suddenly rent and fractured. This primary resistance re- 

 moved, the full power of the elevatory force would be brought to bear 

 upon the disjointed mass, and the surplus energy expended in at once 

 rapidly forcing forward and tilting up the now yielding strata along the 

 line of fracture to that position and that height required to restore a 

 state of equilibrium and no more. It is not i^ossible for any number of 

 minor forces, where the ultimate resistance exceeds each one taken 

 separately, to accomplish iu any time, however long, that which requires 

 for its execution a major force of infinitely greater power. 



Either a minor force, if sufficient to move a given weight, will go on 

 moving, or else, if from any cause a further or secondary and independ- 

 ent resistance, such as in this case that dependent on the cohesion of 

 the strata, has to be met, additional power must be brought to bear, 

 which, if that secondary resistance be then overcome, the cumulated 

 force, being far in excess of the residual resistance, will be immediately 

 expended with energy in proportion to the magnitude of the resistance 

 mastered. Thus, although a railway-engine could readily move ten car- 

 riages, it could not move one hundred. It is true that if it were allowed 

 to proceed with ten carriages at a time it could perform the removal of 

 the whole in ten journeys, but if that were not practicable it w ould re- 

 quire the simultaneous application, say of ten engines, to accomplish 

 the same journey at one time, and by no other means could the inertia 

 of the mass be overcome, although when once overcome the force em- 

 ployed would be largely in excess of that required for traction only. 



Again, in the case of large faults traversing thick masses of strata, 

 the conditions are nearly the same. For example, in the great Craven 

 fault, which brings the disjointed edges of the Silurian rocks on a level 

 Mith the disjointed edges of the Coal-Measures, the extent of displace- 

 ment is in places as much as 4,000 feet, and the range of the fault ex- 

 ceeds 50 miles. If we take the thickness of the strata so fractured at 

 20,000 or any greater number of feet, it is not possible to conceive any 

 small force ficting through any length of time to have effected their dis- 

 ruption, unless it could be imagined that the fault had proceeded pro- 

 gressivelj' with the gradual accumulation of the strata, which is impossi- 

 ble. In any way, the fracture must have occurred suddenly at the 

 moment the tension overcame the resistance of the mass ; it then neces- 



