106 



KNOAA^^LEDGE • 



[March 1, 1889. 



how lonf this village had teen buried no one knew, as no 

 records could anywhere be found to throw light upon the 

 subject. The existence of buried cities beneath the sands of 

 E^ypt is well known, parts of the higher buildings rising 

 like monuments above the desert to mark the tombs beneath. 



On the shores of the Bay of Biscay the drifting sand 

 travels inland at a rate of about 1 G feet in a year, whUe in 

 some parts of Denmark the rate of encroachment reaches 

 24 feet in the same time. A survey made some years ago 

 in Southern India showed that the movement of sand hills 

 with the prevailing wind reached the high average of 

 17 yards per annum. 



The advance of drifting sand may sometimes be checked 

 by planting the dunes with the cluster pine, sand marram, 

 &c. ; these form a network of rootlets binding the sand 

 together, which, with their protective covering of vegeta- 

 tion, prevents further drifting. Sir Wyville Thomson 

 gives a graphic account of the celebrated " sand glacier " at 

 Elbow Bay, in the Bermudas ; it is a dune of pure white 

 coral sand, which has filled a valley, and is slowly advancing 

 inland in a mass 2.5 feet thick ; it threatens to overwhelm 

 cottages and woods, and could only be arrested by the 

 planting of the native juniper and oleander. Many in- 

 stances occur in the Bermudas of houses and woods being 

 buried beneath these coral sand dunes. 



Occasionally, blown sand is mixed with fragments of 

 shells or othef calcareous particles. Eain-water holding 

 carbonic acid in solution may then dissolve these fragments, 

 and rearrange the lime as a cement, and this binds the grains 

 together and forms a friable sandstone. Xear Newquay, in 

 Cornwall, sandstone of this recent subaerial formation 

 occurs in cliffs of considerable height, and the hardest 

 varieties have been used in the construction of Cranstock 

 Church and many other buildings in the neighbourhood. 

 The curious cylinders of indurated sand — " Pixie Holes ' — 

 occurring at Little Fistral, in the same neighbourhood, are 

 the result of similar consolidation ; the sand was com- 

 pacted into a solid mass by means of the calcareous cement, 

 and part of this was again subsequently removed by perco- 

 lating water. 



In the island of Bermudas — which is simply a large bank 

 of di'ifted coral sand — the only rock occurring is " a white 

 granular limestone " formed by the same chemical process. 



On the coast of Gascony, where sand dunes extend for 

 over a hundred miles, more elaboi-ate means had to be 

 adopted in order to save the land from being buried beneath 

 the drifting sand. A wooden palisade was erected along the 

 shore, and as the sand drifting against it accumulated and 

 increased in height, the palisade was continually raised 

 until it reached au altitude sufficient to bar the progress of 

 the sand. 



Drifting sand may be carried to a great height by a 

 strong wind. In our country, during gales, when the sand 

 is dry it may be airried up 200 feet or more ; but in the 

 sand-storms of the deserts, when " sandspouts " occur, it 

 probably reaches a much greater height than this. In the 

 spring of 1SS2 a remarkable sand-storm raged in Iceland 

 for two weeks. The air was so filled with grains of fine 

 sand that it was impossible to see objects a few yards off, 

 and though the sky was clear of clouds the sun was 

 rarely seen. Like the fine volcanic dust that overwhelmed 

 Pompeii, this sand penetrated through the smallest cracks 

 and crevices, entering the houses, and becoming mixed up 

 with the food. Thousands of sheep and horses died owing 

 to the sand being drawn into their lungs at every in- 

 spiration. 



At the late Bath meeting of the British Association, in 

 an interesting communication by General Strachey on the 

 " Sea Temperature in the neighbourhood of Cape Guai-dafui," 



it was shown tliat this cape, the most eastern point of 

 Africa, was, owing to the large and continued increase in 

 the number of ships frequenting the canal route, one of the 

 most important headlands in the world. Homeward-bound 

 vessels from the East by the canal make for Guardafui, just 

 as ships bound for the English Channel steer for the Lizard. 

 During the period of the south-west monsoon, and especially 

 from June to August, the vicinity of Cape Guardafui is 

 enshrouded in a dense haze, extending far out to sea. Xow, 

 this haze is due to the suspension in the air of great quan- 

 tities of fine sand, which have been brought bj' the wind 

 from the African deserts. Vessels thus have great difficulty 

 in making the land, many are frequently lost, and the 

 navigation of the coast is fraught with much danger 

 through the action of wind-borne sand. 



Wherever drifting sand is continually blown against hard 

 rock it polishes the surface by its constant friction. The 

 hard granite cliffs on the Cornish coast are polished and 

 fun-owed in this way, and the Egj-ptian monuments, where 

 exposed to the sand-laden winds of the Libyan desert, pre- 

 sent a .similar polished appeai^ance. 



At the Edinburgh meeting of the British Association in 

 1871, Mr. Grieve described some lai-ge masses of limestone 

 occurring on the shore near Burntisland which were 

 polished by drifting sand, and through the means of which 

 he discovered a new species of a coal measure fossil plant — 

 Dictyoxylon Grievi — occurring in the limestone. 



Many of the desert pebbles are beautifully polished, 

 having a remarkable and characteristic varnished appear- 

 ance, owing to the action of drifting sand, and the scooping 

 out of the dry tcadi/s of Palestine has been effected by the 

 same means. 



In connection with this, Mr. Blake has described the 

 action of diifting sand in the P<iss of San Bernardino, 

 California. He says that the surface of the granite forming 

 the projecting spurs of the mountain of San Gorgonio was 

 beautifully grooved and polished, and long and parallel 

 furrows were cut out by the abrading action of drift- 

 ing sand. The hardest minerals present in the granite — 

 quartz, tourmaline, and garnets — were all cut down and 

 left with polished surfaces. An interesting fact was 

 that some of the garnets, being harder and less easily 

 worn than the other minerals, were left standing in 

 relief upon long pedicles of felspar that had been more 

 quickly worn away. On the lee side of some of these 

 garnets the felspar was protected from the advancing sand, 

 so that it frequently stood out in ridges to the leeward 

 of the gems. It was easy thus to see which was the direc- 

 tion of the prevailing wind, and Mr. Blake says : " These 

 little needles of felspar, tipped with garnets, stood out from 

 the body of the rock in horizontal lines, pointing like 

 jewelled fingers in the direction of the prevailing wind." 



Pillars of Sand suppobting Pebbles ob Shells. 

 1 



! I have often observed a similar phenomenon in walking 

 I along the sands between Bournemouth and Poole Harbour ; 

 dry sand is frequently blown rapidly along the surface of the 

 beach left wet by the retreating tide, the wet sand being 

 usually crowded with pebbles or shells. On the higher part 

 of the beach, where the sand is blown violently against 

 these pebbles, &c., they resist the advancing sand and pro- 

 tect that on the lee side of them ; the wet sand, too, behind 

 the pebbles, owing to the protection it receives, is not dried 

 so quickly as the sui-rounding sand, and the result of this 

 action is that the pebbles and shells are left standing on 



