counties of Devon and Dorset. These eastern streams are comparatively slow and still-flowing. The Dartmoor rivers, rapid, dashing, and rocky, are famous trout streams. None have courses of any great length.
The geological formations of Devonshire are of course the main cause of the general appearance of the county. Dartmoor, as has been said, is a granite region. By far the greater part of central Devon is occupied by Carboniferous rocks, consisting chiefly of sandstones, often siliceous, and of slates. All this formation has been subjected to great disturbances, and the strata (as may be seen on every part of the coast between Boscastle and the mouth of the Taw), are twisted in a manner which defies description, the result being some very extraordinary and picturesque cliff scenery. True coal does not exist, but anthracite occurs near Bideford. These rocks are also associated with trappean and other ashes, which bear a striking analogy to those of existing volcanoes. Underlying the carbonaceous deposits are the grauwacke or Devonian rocks, forming the extreme north of the county, and great part of the South Hams. They extend west of Plymouth, and cover the greater part of Cornwall. These rocks are generally held to be the equivalents of the “ Old Red” system, although the characteristic Old Red rocks, so largely developed in Scotland, Herefordshire, and elsewhere, are not found at all in Devonshire. The Devonian rocks consist of clay-slates, grey limestones, brown sandstones, and flags. The fossils of the two series also differ ; but although these Devonians offer many complexities, this and other differences seem capable of explanation. The third great formation of Devonshire is the New Red, which occupies much of the eastern portion of the county, extends along the coast from Sidmouth to Torbay, and sends out a long spur westward into the Carboniferous district. The upper beds of the series consist principally of marls, the middle of sandstones, and the lower of breccias or coarse conglomerates, coloured red by peroxide of iron. The formation is characterized by a scarcity of organic remains, and by the extreme fertility of some of its soils.
At or near the junction of the Carboniferous and New Red formations, from Washfield, near Tiverton, on the N. to Haldon on the S., occur numerous masses of igneous rock, feldspathic traps. These traps are for the most part excellent building stones, and many of the quarries have been worked for ages. Greenstones and elvans are also associated with the Devonian series. Greensand strata cap the Blackdown hills, and the heights near Axminster, Seaton, and Sidmouth, and, with beds of chalk, occupy a depression in the coast at Beer (near the eastern border of Devonshire), coming down to the level of the sea at Beer Head. A very interesting and remarkable Tertiary deposit, belonging to the Lower Miocene period, occurs at Bovey Tracy, below the eastern escarpment of Dartmoor. It consists of beds of lignite, clay, and sand, with an aggregate thickness of more than 100 feet. In the lignites at least 50 species of plants have been found, all indicating a sub-tropical climate ; but the greater part of the lignite beds is formed by fragments of an enormous coniferous tree, belonging to the genus Sequoia, the only living species of which are to be found in California. Great lumps of inspissated resin occur occasionally. The clay which overlies the lignites is of much more modern date, and contains leaves of the dwarf birch, now an arctic plant, and of 3 species of willow, which all betoken a much colder climate than that of Devonshire at present. Fine potters' clay occurs above this “ head” of coarse clay and sand, and has been turned to account. The lignite called “ Boveycoal” burns with a disagreeable smell, and is not much used.
The ossiferous caverns of Devonshire are famous in geological history. The most important is Kent's Hole, near Torquay, which has been carefully explored, and appears to have been frequented by bears, hyænas, and, at last, by primitive man. There are others at Brixham, at Chudleigh, and at Oreston near Plymouth.[1]
Minerals.—The minerals of most account are tin and copper. Iron occurs, but to no great extent. The silver-lead mines at Combe Martin on the N. coast, and at Beer Alston, on the Devonshire side of the Tamar, were formerly worked to advantage ; but the former have long been abandoned, and the latter, since 1860, have been swamped by water from the river, under the bed of which the principal mine extended. Tin has been found on Dartmoor (in stream works) from an unknown period. Copper was not much worked before the end of the last century. Tin occurs in the granite of Dartmoor, and along its borders, but rather where the Devonian than where the Carboniferous rocks border the granite. It is found most plentifully in the district which surrounds Tavistock, which, for tin and other ores, is in effect the great mining district of the county. Here, about 4 miles from Tavistock, are the Devon Great Consols mines, which from 1843 to 1871 were among the richest copper mines in the world, and by far the largest and most profitable in the kingdom. The divided profits during this period amounted to Pound1,192,960. But the mining interests of Devonshire are affected by the same causes, and in the same way, as those of Cornwall. The quantity of ore has greatly diminished, and the cost of raising it from the deep mines prevents competition with foreign markets. In many mines tin underlies the general depth of the copper, and is worked when the latter has been exhausted. The metalliferous character of the Tavistock district is indeed very mixed, and besides tin and copper, ores of zinc and iron are largely distributed, but these have as yet received no great attention. At the Devon Great Consols more than 2000 tons of refined arsenic are annually produced by elimination from the iron pyrites contained in the various lodes. This amount is calculated to be about one-third of the arsenic produced throughout Europe. Manganese occurs in the neighbourhood of Exeter, in the valley of the Teign, and in N. Devon ; but the most profitable mines, which are shallow, are, like those of tin and copper, in the Tavistock district. The other mineral productions of the county consist of marbles, building-stones, slates, and potters' clay. Marbles occur in the Carboniferous series at Chudleigh and elsewhere, but of very inferior character and beauty to those among the Devonian rocks, at Ipplepen, Babbacombe near Torquay, and Plymouth. These are largely worked, and are used extensively in the decoration of churches and other buildings. Among building stones, the granite of Dartmoor holds the foremost place. It is much quarried near Prince Town, near Moreton Hampstead on the N. of Dartmoor, and elsewhere. The annual export is considerable. There are very large and ancient quarries of a chalky greensand at Beer, near the eastern border of the county. This is an excellent building-stone, nearly white, and composed of carbonate of lime, mixed with argillaceous and siliceous matter, and with particles of green silicate of iron. Hard traps, which occur in many places, are also much used, as are the limestones of Buckfastleigh and of Plymouth. The Roborough stone, used from an early period in Devonshire churches, is found near Tavistock, and is a hard, porphyritic elvan, taking a fine polish. Excellent roofing slates occur in the Devonian series round the S. part of Dartmoor. The chief quarries are near Ashbur-
- ↑ For a full account of the literature connected with the caverns, and of the discoveries made in them, see Transactions of the Devonshire Association, and the annual reports, by Mr W. Pengelly, of the committee appointed by the British Association in 1864.
