The highest in the Mainland is Ronas Hill, Northmavine, a great mass of red granite, rising to a height of 1475 feet, forming the culminating point of the North Roe tableland, and having the hilly ridge of the Björgs on its eastern side. A long range of hills extends through the parish of Delting, from Firth Ness to Olnafirth; and from the south side of that inlet it extends southward to Russa Ness on the west side of Weisdale Voe. This is the loftiest range, and the southern ridge forms a complete barrier between the east and west side of that part of the Mainland. The highest hill in this chain is Scallafield, 921 feet. Other two parallel ridges lie east of this, the one from the east side of Weisdale Voe to Dales Voe in Delting; and the other from near Scalloway in a north-east direction to Collafirth. There are breaks in these hilly ridges, notably where the county road crosses over near Sandwater, and again between Olnafirth on the west and Dury Voe on the east. The other range worthy of note extends from the Wart of Scousburgh in Dunrossness, with intervening breaks, to the east of Scalloway, where it divides into two ridges, and stretches onward to the east and west sides of Dales Voe. Fitful Head in the south, 928 feet; Sandness Hill in the west, 817 feet; the Sneug in Foula, 1372 feet; the Wart of Bressay, 742 feet; and the Noup of Noss, 592 feet, are conspicuous land-marks round the coast. The island of Yell is hilly, with parallel ridges running north-east and south-west—highest point, the Ward of Otterswick. A range of hills extends along the west side of Unst—highest point, Vallafield, 708 feet. In the extreme north is Hermaness, 657 feet; while on the opposite side of Burrafirth is the still higher hill of Saxa Vord, 934 feet.
In the larger islands the land is generally lower on the east side than on the west; and in many cases the hills are steeper on the west than on the east. Most of the smaller islands are low-lying and grassy, forming excellent pasture ground for sheep.
There are many fresh-water lochs in the islands, the largest being Girlsta Loch in Tingwall, Loch of Cliff in Unst, and Spiggie in Dunrossness. They are nearly all well stocked with trout, which makes Shetland attractive to anglers. Shetland has no streams large enough to be called rivers; but it has burns in plenty, rippling brooks in summer and brawling torrents of brown peaty water in winter, when the soil is sodden with rain or snow.
5. Geology and Soil
The geological map shows that metamorphic rocks cover the greater part of Shetland. These rocks are represented by the clayslates and schists that extend from Fitful Head to the Mull of Eswick; and by the gneiss found from Scalloway to Delting, and also on Burra Isle and Trondra, Whalsay and Skerries, Yell, the west side of Unst and of Fetlar, the east side of Northmavine, and the north sea-board of the Sandness-Aithsting peninsula. Associated with the two series of metamorphic rock are bands of quartzite; while at Fladdabister, Tingwall, Whiteness, Weisdale, Northmavine and Unst are beds of limestone.
The geological formation of Unst is interesting. The gneiss on the west is succeeded by a band of mica, chlorite and graphite schists. Next come zones of serpentine and gabbro, to be followed by schistose rocks at Muness. Fetlar shows a similar formation.
Of the igneous rocks we may mention first the intrusive granites of Northmavine, Muckle Roe, Vementry, Papa Stour, Melby and South Sandsting. A bed of diorite extends from Ronas Voe to Olnafirth. Part of Muckle Roe also shows diorite. Syenite occurs round Loch Spiggie and is traced northward through Oxna and Hildasay to Bixter and Aith. Lava, tuff, and other volcanic materials appear in various parts of the islands, as between Stennis and Ockran Head, in Northmavine, Papa Stour, the Holm of Melby, Vementry and Bressay.
The predominating sedimentary rocks in Shetland belong to the Old Red Sandstone formation. These are found from Sumburgh Head to Rova Head, and in Fair Isle, Mousa and Bressay. The fault or boundary line between them and the metamorphic rocks is clearly traceable at various points along the east of the Mainland. Foula, Sandness and Papa Stour, on the west, show remnants of Old Red Sandstone. This formation is believed to have once covered the whole area now represented by the Shetlands. To the same geological period the hardened sandstone is considered to belong, which occurs in the western peninsula, covering most of the district of Sandness, Walls, Sandsting and Aithsting.
Glacial phenomena—striae, moraines, boulders—are interesting features in the geology of Shetland. Over Unst, Fetlar, Yell and the north of Mainland the movement of the ice had been uniformly from east to west. Over the middle and southern districts, the glaciers had curved in a north-westerly direction.
The variety of rocks accounts for the variety of soils in the islands. There are many fertile regions of sandy and loamy soil. Perhaps the best is the limestone district of Tingwall. Most of the county, however, is covered with peat moss and peaty soil.