12 



ties. The last column gives the corresponding value of the space (s ) 

 through which a particle of the water, or any body floating in the 

 water, will be carried by the wave. The expressions for s and s are 



2 Vv { 



s ° ~ Y " v * ' 



V being much greater than u,. [See preceding page.] 



In estimating the magnitude of a block which may be moved by a 

 given current, the transport is supposed to take place over a hori- 

 zontal surface sufficiently hard and even for the block to roll upon it 

 without impediment. In other states of the surface the transport 

 might be more or less impeded. The constant action of denuding 

 causes would be highly favourable to the transport by the successive 

 removal of local impediments. The author conceives that the ob- 

 jection to this mode of transport, founded on inequalities of surface 

 which now exist between the original site of a block and its present 

 position, have been far too much insisted on by some geologists, 

 for, he contends, such inequalities could not generally exist under 

 the continued action of denuding causes, among the most powerful 

 of which may be reckoned the transporting currents themselves. 



It should be remarked, that it appears from the values of 5 given 

 in the preceding table, that the space through which any consider- 

 able block could be moved by a single wave of elevation, is only 

 equal to a small fraction of the breadth of the wave. Consequently, 

 if such a block has been moved by this agency to a considerable di- 

 stance from its original site, the transport must have been effected by 

 a repetition of transporting waves ; and, therefore, since a wave of 

 considerable height can only be produced by a sudden elevation, this 

 theory of transport is ultimately associated with the theory which 

 attributes the more marked phsenomena of geological elevation to a 

 repetition of paroxysmal movements. 



The author concludes with some general observations on the evi- 

 dence by which we may hope to distinguish between the effects of 

 the three different agencies to which the transport of blocks may be 

 attributed — glaciers, floating ice, and currents of water. Large an- 

 gular blocks in the immediate neighbourhood of glacial mountains 

 (such as the alpine blocks) may doubtless, in many cases, be referred 

 to glaciers, while the transport of similar blocks to great distances 

 may be referred to floating ice. Smooth rounded blocks of smaller 

 dimensions, especially when spread out with other detrital matter in 

 layers of considerable horizontal extent, the author would refer to 

 the action of aqueous currents. 



