December 2, 1889.] 



KNOWLEDGE. 



23 



yet the potency of sand under its influence upon sandstone 

 cannot be gainsaid.* 



The softer sandstones of the Hastings series in the 

 south-east of England lend themselves readily to this 

 process of weathering, as is well seen in the neighbour- 

 hood of Tunbridge Wells, at West Hoathly, and elsewhere 

 in Sussex, and has been well illustrated in Mr. Topley's 

 Gcdhiiiy iif the U'l'iihl. On Rusthall Common, Tunbridge 

 Wells, stands the Toad-rock, one of the most striking of 

 such pinnacles. Situated in a hollow on the upland 



*^^.^i^;-- 



The Toad Rock, Rdsthall Common. 



heath, snirounded by low cliff-like exposures of the same 

 sanilstiiiir, this rock-mass shows very plainly the eft'ects 

 of the greater impregnation of some of its layers with iron- 

 oxide in resisting the weather, and the action of the sand. 

 Its base is ankle-deep in white sand ; and as surely as we 

 attribute the pot-hole, hollowed in the hard rock beside 

 the bed of the mountain torrent, to the gyrations of the 

 pebbles that now lie within it in the eddies of the stream, 

 so surely do .we assign to this sand, whirled round the 

 pedestal of the toad-like mass, the grooves cut all round 

 this pedestal as if tiu-ned in a lathe. Harrison's Rocks, 

 near by, are but a less complete exemplification of the 



* Tho cutting powei- of Band, like the force of a blow, varies with 

 the 8C|uaro of tho velocity of tho missile — according to experiments 

 described at the Meteorological Society's meeting in May last by Mr. 

 W. 11. Dines. It was found that a pressure gauge, made to whirl round 

 at the end of a long arm by steam jiower, registered a pressure of I lb. 

 per square foot with a velocity of a little more than 17 miles per 

 hour. Consequently, a wind of li!) miles per hour (which would be a 

 very exceptionally liigh wind for England) would give a pressure of 

 about 1(> lbs. per square foot, and a pressure of iiOO lbs. per square 

 in<'h would bo given by a wind blowing with a velocity of 850 miles 

 per hour. I am not disposed to attribute such cutting power to sand 

 blown by winds as Professor Boulger seems inclined to. The sharp- 

 ness of many Egyptian carvings and inscrii)tions which have been 

 bombarded by desert sand for 3,000 years is very remarkable. They 

 are, however, generally cut in very hard rock, and have not been 

 exposed to frost and rain. — A. C. Uanvaki>. 



NoTK ON Mr. Kanvakd's Notk. — It is perhaps the unden-utting that 

 most clearly exempliiies blown-sand action, this not being, I think, ex- 

 plicable liy mere rain and frost. The examples I have quoted are in 

 sandstone or limestone, not in granite or harder rocks. — G. ><. Boui.ii kr. 



same process. At West Hoathly it is in the same series 

 of sandstones — the upper beds of the Lower Tunbridge 

 Wells sand, a sub-division of the Hastings series — 

 that the rock-pinnacles, now in the private groimds of 

 Rockhurst, occur. " Great-upon-Little," the most famous 







Harrison's Rocks, near Tlnbridoe Wells. 



mass, is estimated to weigh between 400 and 500 tons, 

 and is so poised upon its undercut pedestal as to be 

 slightly movable. Though there has here been some 

 slippmg, the isolation of the great blocks can be seen to be 

 prima.rily due to weathering along joints. It is mteresting 

 to notice here, in the shady hollows, the FUmy Fern 

 (Hi/menoplii/lhiiii tunbrid(jenx<') which once graced the 

 sister pinnacles of Kent. 



It is probably to entirely similar causes that we may 

 attribute the often erroneously described Agglestone of 

 Studland Heath, Dorsetshire. Tradition tells us that this 

 mass of iron-shot sand, estimated to weigh 100 tons, was 

 dropped by the Prince of Darkness himself, chief of all 

 " aggies," "hags, witches or warlocks, who had intended it 

 for the destruction of Wimborne Jlinster or Salisbury 

 Cathedral. " Guide " books speak of it as " druidical." and 

 geologists, who can never have examined it, as a transported 

 " Sarsen-stone." A slight examination of the steep little 

 conical hillock, resembling a tunmlus, on which it is 

 perched, reveals tiic fact that it is part and parcel of this 

 said mound, and is, in fact, but an extra hard portion of 

 those Ikgshot sands that form the whole heath and crop 

 out so picturesquely in the Pamted Kocks of Studland 

 Bay. The resistance of a strongly impregnated iron -sand 

 to the weather is the secret of its existence. 



Did we go farther afield, to the arid plateaux of 

 C!olorado, we might tind written yet more legibly, because 

 not so obliterated by rain or frost, the tale of Nature's 

 sand-blast. Here level plains, thousands of square miles 

 in extent, intersected by canons carved perpendicularly 

 thousands of feet down through horizontal limestones, 

 sandstones and shales, liavo been lowered by tho removal 

 of strata thousands of feet in thickness. The proof of this 

 lies in the many-coloured cliffs whose projecting sand- 

 polished ledges were the home of the ancient cliff-dwellers. 



