662 



PROF. T. M C KE^NY HUGHES OlST THE ANCIENT 



gafa being the most common, as on the adjoining sand-dunes. Sea- 

 shells are rare, and only such as might have been carried by birds 

 or rolled up the sand-slope by the wind. 



In the lower part of the sand-cliff, however, sea-shells are com- 

 mon, and there are lines of shore shingle which generally forms an 

 irregular conglomerate at the base. It is consolidated into a hard 

 calcareous sandstone, so hard that it is used in the neighbourhood 

 for rough walling. Owing to its being but little jointed, it long- 

 resists the battering of the waves, which have to remove it almost 

 grain b} 7 grain. Here and there, however, great masses are lifted 

 out and trundled by the waves along the shore, furnishing an 

 example of the sea quarrying out and moving along the shore, at the 

 same level as the boulders of granite, masses as large as, if not larger 

 than, those for the transport of which ice-agency is invoked. One 

 such, resting on the cleaved rocks at the foot of the cliff, is shown on 

 the left-hand side of fig. 4. 



The consolidation of the blown sand round the coast of Devon 

 and Cornwall was noticed and explained by Paris *, who ascertained 

 by experiment that the shelly sand contained from 60 to 64 per 

 cent, of carbonate of lime. Boase t describes the same thing, and 

 quotes an old author Avho, fifty years before his time, explained the 

 induration of the sand by infiltration of water charged with car- 

 bonate of lime, only he described it as sparry or coralline juice, such 

 as forms incrustations in the bottoms of culinary vessels and in 

 water-pipes. In a little ravine about half a mile west of Middle 

 Borough I noticed a section as of a transverse gully about twenty 

 feet deep, at the base of which, under some seventeen feet of talus, 

 was three feet of sand, in which were bands about an inch thick of 

 a dark sandy ironstone. This also seemed to be quite a recent 

 formation. 



Where the sand from above has run down through a crevice, like 

 sand in an hour-glass, it has often eaten out a cylindrical hole 

 from two to four feet across. I am inclined to think from what I 

 have seen that, except where there has been a hole quite through, 

 these chimneys are never formed, but that some of them are origi- 

 nally half-cylinders, that is to say, the sand pouring over the edge 

 of a sand-cliff cuts a groove out as would water. I think it certain 

 that when once formed the wind helps to carry on the work and 

 round them off, but that the action of the wind on the top of the 

 sand could never form them by producing a rotatory motion, as the 

 water of an eddying mountain-torrent bores holes in the solid rock 

 by whirling pebbles round in any hollow that arrests them. 



Flints occur in this ancient beach as on the modern shore, and 

 there has been much speculation as to their origin and mode of 

 transport. An examination of the flints themselves will, I think, 



* Paris, " Geological Structure of Cornwall,'' Trans. B. Geol. Soc. Cornwall, 

 vol. i. 1818, p. 194 



t Boase, " On the Submersion of part of the Mount's Bay," &c, Trans. E. 

 Geol. Soc. Cornwall, vol. ii. 1822, p. 143. See also Carrie, "On the Mineral 

 Productions of St. Just," ibid. p. 333. 



