HARDWICKE'S SCIENCE-GOSSIP. 



207 



survey of the rock in question. On the shore fore- 

 nent the village of Lochinver, there are to be found 

 numerous beautifully-rounded pebbles of grit and 

 conglomerate, but none of gneiss, and no fine sand 

 whatsoever. Moreover, the comparative uniformity 

 of the lay of the latter formation is conspicuously 

 apparent to any one who has climbed the heights and 

 so surveyed it from an elevation. 



The Lower Silurian formation is well developed in 

 Sutherland, consisting in its fullest range of a sand- 

 stone series at the base divisible into two zones, a 

 partly calcareous and partly sandy series in the 

 middle in three zones, and a markedly calcareous 

 series in seven zones at the top. These strata almost 

 invariably overlie the arch?ean gneiss and not the 

 Cambrian rocks, the latter being now scattered 

 either in isolated patches near the ^seaboard, or pro- 

 jected upwards to form picturesque mountains. Two 

 areas on the north coast known as the Durness and 

 EriboU exhibit the most conspicuous development of 

 the Silurian system. In the former or western area 

 all the series as indicated above are represented ; but 

 the upper limestone series is specially predominant. 

 Owing to excessive disturbance by faults, the position 

 of the strata is very irregular and uneven, yet their 

 thickness, according to estimation, is not less than 

 2,000 feet. Twelve zones in all have been detected 

 from a basal breccia and quartzite, through " fucoid " 

 calcareous rocks of various kinds, and " serpulite 

 grit " of dolomite, with very marked mineral 

 characters and fossils, up into the feeven well-defined 

 limestone groups at the top, well charged with fossil 

 trilobites, annehds, sponges, &c. — the whole com- 

 prising a very decidedly conspicuous and well con- 

 trasted area extending in a sort of tiiangle. 



Between this and the Eriboll or eastern basin there 

 is a prominent ridge of archsean gneiss, which has 

 doubtless been projected from below, shattering and. 

 faulting the overlying beds. Both the western and 

 the eastern slopes of this ridge are covered by huge 

 fragments and patches of the displayed Silurian quartz- 

 ite. On the west shore of Loch Eriboll there is 

 nothing exposed save some grits and "sago-pudding" 

 quartzites ; but on the east shore, at Ant Sron, there 

 is a fine development of calcareous mudstones and 

 bands of dolomite, with overlying dolomites, grits, 

 quartzites, and cleaved shales. These pass under- 

 neath dark serpulite limestones ; and these, again, 

 rapidly give way to unfossiliferous flags and 

 dolomites, and so end the series here (the higher 

 fossiliferous limestones of the Durness area not being 

 found). The strata just described exhibit some very 

 remarkable phenomena, e.g. numerous flexures, and 

 a peculiar aspect of their sharp anticlinal folds, the 

 west limbs of which are sometimes vertical or in- 

 verted, or broken by what is called a reversed fault 

 (i.e. a sloping fault where the under side of the 

 strata of the rocks which have sunk down makes an 

 obtuse angle with the plane of the fault). The eftect 



of these disturbances is, that in traversing the ground 

 the different layers or zones of the beds are seen to 

 be repeated again and again, lower zones sometimes 

 apparently overlying higher ones. Eventually, at 

 various points, by the force of a great reversed fault 

 or thrust-plane (i.e. a reversed fault at so very low 

 an incline that the rocks on the up-throw side have 

 been, as it were, pushed horizontally forward), the 

 archaean gneiss has been violently thrust up from below 

 and projected bodily over the fossiliferous Silurian 

 strata. Furthei; eastwards, again, another great 

 thrust-plane is encountered ushering in a certain 

 series of highly-metamorphosed schists and gneissoid 

 rocks known as the " upper gneiss," or the " igneous 

 rock," which bear unec}uivocal traces of tremendous 

 mechanical energy. A similar schistose series with a 

 similar order of succession in the beds having been 

 discovered lying isolated near Durness, about ten 

 miles westwards, the learned geologist has con- 

 jectured — or rather concluded — that the latter rocks 

 have been pushed forwards for this distance along 

 the surface of this upper and more energetic thrust- 

 plane, i.e. the rocks along the upper thrust-plane 

 override all the other rocks pushed forward by the 

 lower thrust-planes in the Eriboll area, and rest 

 directly on the limestones of the Durness basin. 

 The savant, scratching some mathematical angularity 

 on his elaborate map, and finding some lines or other 

 to " coincide," hastens to the decision that geological 

 or mineralogical phenomena obsequiously obey 

 geometrical formula;. Reviewing, however, the 

 remarkable features here detailed, it may be useful to 

 append, that there can be little doubt about the fact 

 of prodigious terrestrial displacements having taken 

 place ; but that they differ little from what has 

 occurred all over the world where the requisite con- 

 ditions exist, more especially the presence of a 

 highly tough and unyielding chemical compound in 

 association with a material much simpler and more 

 sensitive as to molecular and mechanical energy. 



The Old Red Sandstone (lower division) is repre- 

 sented in Sutherland by numerous patches and 

 outliers in various places, such as on the east shore 

 and hill-ground of the Kyle of Tongue and thence 

 towards Ben Stomino, also on Ben Armine, on Bens 

 Griam More and Beg, etc., about Strathy Bay, and 

 along a great belt, five miles broad, on the east sea- 

 board. These beds consist mainly of a very coarse, 

 dirty, red conglomerate, with red sandstones, red 

 sandy clays, and calcareous flagstones and shales in 

 minor proportions. 



There is a belt about sixteen miles long of Second- 

 ary formations on the east coast of the county. Beds 

 of Triassic age consisting of .sandstone and dirty lime- 

 stone occur on the shore near Dunrobin and Golspie. 

 Following thereon are Lias strata, including sandstone 

 and conglomerates at the base, followed by estuarine 

 sandstones, shales, and very thin coal-seams, gradu- 

 ating into blue micaceous clays and fossiliferous lime- 



