270 JOSEPH TEESTWICH, P.R.S.^, F.G.S., ON A TOSSIBLE 



intercalated hard bands (of flint), these materials (or rather 

 their debris) alternate in the head — not with the regularity of" 

 stratified strata, but irregularly, and with much confusion, 

 the upper bed especially being rolled over and thrown hack, 

 as though by some sudden strong driving force. It is pos- 

 sible to conceive that a rubble of tliis character might have 

 been projected on the old chff by an ice or snow slide, w^ere 

 it not for the objections I have before urged, and the fact of 

 finding, as at Brighton, large angular blocks of rock that have 

 been transported from a distance of a mile or more inland, 

 and must have required considerable force to move. At the 

 same time there are intercalated beds of fine chalk silt, 

 sometimes laminated, and at Sangatte containing uninjured 

 fragile L-ind shells, which could not have been subjected to 

 rough treatment. A body of water acting under great 

 pressure, and with varying velocity as the land rose, could, 

 1 conceive, alone have accomplished these variable results. 



The late Mr. Hopkins* of Cambridge has shown that, if a 

 considerable area at the bottom of the sea were suddenly 

 elevated, a icave of translation^, accompanied by a current, 

 the velocity of which would depend principally upon the 

 depth of the sea, would diverge in all directions from the 

 central disturbance. Calculations, he says, " prove beyond 

 all doubt that paroxysmal elevations, beneath the sea, 

 varying from 50 to 100 feet in height, may produce currents 

 of which the velocities shall vary from at least 5 or 6 to 

 15 or 20 miles an hour, provided the depth of the sea do not 

 exceed 800 or 1,000 feet." In considering the magnitude of 

 the blocks which might be moved, he fourd that the force 

 exerted on a surface of given magnitude increases as the square 

 of the velocity, and that it " varies as the sixth poicer of the 

 velocity of the ciirrentr But the movements must be repeated 

 for large blocks to travel beyond short distances. 



It is evident that we have in this form of disturbance an 

 engine of enormous poAver, and, though our hypothesis does 

 not deal with the greater movements and powerful currents 

 contemplated by ]\Ir. Hopkins, we may iiifer what the results 

 might be with changes havhig even only a fraction of such 

 magnitude. Movements of this character would, like Nas- 

 myth's hammer, be capable at times, when the uplift was rapid, 

 of exerting enormous force; while at other times, when the 



* Quart. Journ. Geol. Sue, vol. iv, p. 90. 



