476 Mr. Hopkins on the Lake District. 



miles an hour, if we allow of paroxysmal elevations* of from 100 

 to 200 feet. This velocity will decrease as the wave expands, 

 unless the current be constrained to pass through a comparatively 

 narrow channel, like that which must have been formed by the pass 

 Stainmoor when just submerged beneath the surface of the ocean. 

 In such case the velocity of the current might be much increased. 



With respect to the magnitude of the blocks which might be 

 moved by a current of given velocity, the author remarks, that the 

 facility with which the transport of a block may be effected 

 depends principally on its form. The more it approximates to per- 

 fect sphericity, the less, cceteris paribus, will be the force necessary 

 to remove it. The author conceives that there is no doubt what- 

 ever but that blocks, not more spherical than many rolled blocks are 

 observed to be, of five tons weight and upwards, might be moved 

 under favourable circumstances, by a current of ten miles an hour. 

 That the force of a current increases in the ratio of the square of 

 its velocity has been distinctly established by experiment for all 

 velocities up to eleven or twelve miles an hour ; nor does there 

 appear to be any reason for doubting that the same law holds for 

 much greater velocities. Assuming this law, the author states it 

 as the result of a simple calculation, that if a certain current be 

 just able to move a block of given weight and form, another cur- 

 rent of double the velocity of the former would move a block of a 

 similar form, whose weight should be that of the former in the 

 ratio of 2 6 : 1, i.e. of 64 to 1. If the velocity of the second cur- 

 rent were treble that of the first, the weights of the two similar 

 blocks would be in the ratio 3 6 : 1, i. e. of 729 to 1, and so on for 

 other velocities. Hence, if a current of ten miles an hour would 

 move a block of five tons, a current of twenty miles an hour might, 

 under similar circumstances, move one of 320 tons. No transported 

 blocks approximating to this weight appear to have been moved 

 from the Cumbrian mountains. The author, therefore, does not 

 hesitate to affirm the entire adequacy of the cause now explained 

 to transport all the erratic blocks which have been identified as be- 

 inf derived from that region, nor can he therefore hesitate to con- 

 clude that such has been the agency by which that transport has 

 actually been effected. 



It has been urged that no current could carry boulders up the 

 escarpment of the Eastern Wolds of Yorkshire, nor does the author 

 contend for any such effect of currents. Whether the blocks now 

 found on the wolds were transported there by currents or by float- 

 ing ice, the transport must have taken place before that region 

 emerged from the ocean. But the author contends that the forma- 

 tion of such an escarpment as that referred to, or like the oolitic 



* If the extent of country elevated be considerable (like that of the 

 district of the Lakes, for instance) the elevation might occupy several 

 minutes and still produce the great wave above described. If the elevation 

 were produced more slowly, the height of the wave, and consequently the 

 velocity of the current, would be proportionably less. 



