90 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
configuration as at present, when it is elevated above the surface of 
the sea; and thus an apparent difficulty has been created, which 
im my opinion has been much too strongly insisted upon by the op- 
ponents, and too easily admitted by the friends, of this theory. The 
assumption is, as I conceive, entirely untenable in the majority of 
those cases in which it has been made, and is inconsistent with the 
primary hypothesis of the theory,—the existence of currents sufficient 
in force and in frequency to produce the effects in the transport of blocks 
which the theory attributes to them. The difficulty alluded to arise 
from the supposed existence of irregularities of surface, such as deep 
valleys, or high escarpments in directions transverse to the trans- 
portmg currents. And such a valley might undoubtedly be formed 
as the immediate effect of a great dislocation, and such an escarpment 
might be formed by a great fault; but the formation of the one or 
the other, as the effect of great ocean-currents, is altogether imcon- 
ceivable, even supposing these currents to have the most favourable 
directions ; and especially does it become so when we acknowledge 
_ the existence of great transverse currents, under whatever conditions 
they may have existed. Observations likewise on the forms of sub- 
aqueous surfaces, where the water is sufficiently shallow to subject 
them to the action of ocean-currents, prove the great leveling ten- 
dency of such currents. I contend, therefore, that the surfaces over 
which boulders, according to the theory of currents, must have been 
conveyed, presented in general none of those abrupt inequalities, great 
or small, which usually distinguish subaérial surfaces (and which 
would render the transport of blocks across them difficult or impos- 
sible), with the exception of those cases in which the mequalities are 
attributable to elevation and fracture. The case before us of the 
transport of blocks from Shap Fell to the Kastern Wolds of Yorkshire, 
which I shall discuss in the sequel, will serve to elucidate these 
remarks. 
21. Theory of Currents*.—If a considerable area at the bottom of 
the sea were suddenly elevated, nearly the whole supermcumbent 
mass of water would be elevated in nearly the same degree, and a 
great wave, which has been called a wave of translation, would di- 
verge in all directions from the central disturbance, and would be 
accompanied by a current diverging in like manner, the velocity of 
which would depend principally on the depth of the sea, the height 
of the original elevation of the water, and the distance to which 
the wave had been propagated. These currents may be termed 
currents of elevation, and are those alone with which we shall here 
be concerned. I can conceive no others of sufficient power to have 
* In this memoir, as originally presented to the Society, 1 had entered into 
considerable details respecting the nature of a wave of translation, and the effec- 
tiveness of its attendant current in transporting erratic blocks ; but I have not 
thought it necessary to preserve these details, having subsequently given the ma- 
thematical exposition of the subject in the ‘ Transactions of the Cambridge Philo- 
sophical Society,’ vol. viii. part 2,to0 which I would refer the reader. I shall only 
preserve here a few words of general explanation, and some results of calculation 
with their application to the case before us. 
