OCR Text |
Show 262 ACTION OF TilE SEA ON waves having, in their repeated assaults, forced themselves an entrance. This breach, named the Grind of the Navir (No. 8), is widened every winter by the overwhelming surge that, finding a passage through it, separates large stones from its sides, and forces them to a distance of•no less than one hundred and eighty feet. In two or three spots, the fragments which have been detached are brought together in immense heaps, that appear as an accumulation of cubical masses, the product of some quarry*." It is evident from this example, that although the greater indestructibility of some rocks may enable them to withstand, for a longer time, the action of the elements, yet they cannot permanently resist. There are localities in Shetland, in which rocks of almost every variety of mineral composition are suffering disintegration: thus the sea makes great inroads on the clay slate of Fitfel Head, on the serpentine of the Vord Hill in Fetlar, and on the mica-schist of the Bay of Triesta, on the east coast of the same isle, which decomposes in angular blocks. The quartz rock on the east of Walls, and the gneiss and mica-schist of Garthness, suffer the same fate. Such devastation cannot be incessantly committed for thousands of years without dividing islands, until they become at last mere clusters of rocks, the last shreds of masses once continuous. To this state many appear to have been reduced, and innumerable fantastic forms are assumed by rocks adjoining these isles, to which the name of Drongs is applied, as it is to those of similar shape in Feroc. No.9. Granitic rock• namecllhl DrO"H'' bdwetll Papa Stour and Hill•rvlck Pill• "' Ilibbert, p. 528. THE SII!!:TLAND ISLANDS. 263 The granitic rocks (No.9) between Papa Stour nnd Hillswick N· ess afford an example. A still m ore s1. ngu 1a r c1 u ster of rocks Is seen to ·t he south of Hillswick N ess (No . lO ) , w1 u .c h pre-sents a vanety of forms as viewed f d' tr · f b . rom Iuerent pomts, and has o ten een hkened to a small fleet of v esse 1s w1. t h sprea d sai. ls~. No. 10. GrttTlitlc Rockl to the lOut/• qf Hill•ruick Ntll, Shetland. yv e may imagine that in the course of time Hills wick N Itself may present a similar wreck from the unequal d ess · · f 1 k . . ' ecompo- Sltlon? t 1e ~oc s whereof 1t 1s composed, consisting of gneiss and mtca schist, traversed in all directions by veins of fels porphyry. par Midwa! between the groups of Shetland and Orkney is Fair 1Is lan1d·~,r satd toh be composed of sandstone with high perpe n dl' cu-ar1 c Ius.d T e curren. t runs with such velocity ' that d urm· g a ca ~'an. when there 1s no swell, the rocks on its shores are white Wit? the foam of the sea driven against them. The ~rkney~, 1f carefully examined, would probably afford as much dlustratwn of our present topic as the Shetland Islands. 'rhe n;t.h-east :pro~ontory of Sanda, one of these isles, has been cut o m modern times by the sea, so that it became what is now c~lled S~art .Island, where a lighthouse was erected in 180'7 smce whiCh time the new strait has grown broader. ' East Coast of Scotland.-To pass over to the main land f .S cotland ' we fi n d t h at, m· Inverness-shire there have b o mroads of th e sea a t F ort G eorge, and other' s in Murrayshiereen, * Hibbert, p. 519. |