658 



PKOF. T. M'KENNY HUGHES ON THE ANCIENT 



it once commonly rose. He thinks that the " transportation " of the 

 great boulder of red granite " required more than wave-power 

 merely," and, on the assumption that it was carried on ice, points 

 out that it would necessitate a considerable change of level to float 

 such a large mass of ice to where the boulder now lies. Inciden- 

 tally he notices the vertical shafts in the sand-cliffs, and suggests in 

 explanation that the process begins by the infiltration of rain-water 

 containing carbonic acid in solution, which dissolves the calcareous 

 cement of the consolidated sand, and "■ that in periods of continued 

 drought the water evaporates, the winds disperse much of the dry 

 loose sand, but communicate a rotary motion to the residue, and 

 thus produce the cylindrical or subcylindrical form of the shafts, 

 and that by a repetition of this process the shaft is gradually deep- 

 ened until it passes completely through the sand-beds." 



The points to which I invite attention in the following paper 

 are : — 



(1) Is this deposit on the southern slopes of Saunton Down a 



raised beach ? and 



(2) Were the above-mentioned boulders carried to their present 



position by ice ? 



I would avoid any future misapprehension of my meaning by 

 defining what I understand by a raised beach. 



A raised beach is a portion of the shore-deposits which were 

 accumulated when the land was at a lower level. It is not suffi- 

 cient to show that the deposit could not now be laid down by the 

 sea in the position and at the height at which it is found, unless it 

 can be shown also that no other conditions than a sinking of the 

 land would explain its occurrence in such a position or at such a 

 height. 



High-water mark for the purposes of this inquiry does not mean 

 the level to which the tide rises in calm, but the much higher line 

 up to which wind-driven Atlantic waves in spring- tides carry sand, 

 shells, and blocks of stone. The tidal range in Barnstaple Bay is 

 stated by Mr. Hall to be between 38 and 40 feet ; but enormous 

 masses of rock may be seen thrown up to much higher levels in 

 almost any little cove around this coast. 



We know that stones &c. can be caught in the waves * and 

 hurled to the top of vertical walls of rock ; but this does not give a 

 beach-like deposit. If, however, we have a long slope on an open 

 shore, or still more in a narrowing creek or bay, and ocean waves 

 breaking on it, beach-deposits (stones, sand, shells, &c.) are carried 

 far above what is commonly understood by high-water mark. Alter 

 the coast-line, destroy a promontory or sandbank, turn on a current, 

 or change the outfall of a river and the sand and shingle are swept 

 away ; the sea cuts into the solid rock, and leaves a cliff with the 

 thin end of the long shore slope seen on top of it, now many feet 

 above high-water. mark f. 



That is not a raised beach, for it would require no change of 



* Hughes, Journ. Vict. Inst, or Phil. Soc. Gt. Brit., Feb. 1887, p. 4. 

 t Of. Carne, Trans. R. Geol. Soc. Cornwall, vol. ni. 1828, p. 229 et seq. 



