Between the two Devonian areas, and occupying a large part of the centre of the county, are the carboniferous or coal-bearing measures, containing, however, not true coal but anthracite, which has more carbon in it than is found in ordinary coal; and these beds are perhaps more often known as Culm, from the Welsh _cwlwm_, a knot, in allusion to the fragmentary condition in which the mineral is frequently found. Anthracite, which elsewhere and especially in South Wales is a most valuable fuel, is here clayey and impure, and in thin seams. It is worked to a small extent, to be ground and made into a paint called Bideford Black. The Culm measures consist of grits, shales, and sandstones, with beds of chert and limestone containing fossil plants and other forms of marine life. Fish are few, only two species having been identified. The anthracite occurs in the middle Culm, and there are other remains of plants in both the middle and upper beds. The upper Culm is well seen on the coast near Clovelly and by the river Torridge, where it has been bent by volcanic upheaval into curious and beautiful curves. These measures, in general, are characterised by many outcrops of volcanic rock, some of which were probably contemporary, that is to say, they were poured out while the culm was in process of formation; while others are intrusive, or were forced up through the strata after these had been solidified into rock. These igneous rocks are found in great variety. [Illustration: A smoothly-weathered granite Tor, Dartmoor] By far the most important and striking of these volcanic formations is the great granite mass of Dartmoor, one of the most prominent features of the county, measuring 225 square miles in extent, and constituting the largest granitic area in England. Granite is a volcanic rock, formed, it has been suggested, by fusion at a great depth and under great pressure, and consisting in the main of three minerals, quartz, felspar, and mica. That of Dartmoor is, on the whole, grey and coarse-grained, but it varies a good deal in colour, fineness, and composition. Its real origin is obscure. It has been assigned by various experts to various periods, and it has been called "the sphinx of Devon geology." There can, however, be no doubt about the great disturbance which has been caused in the county by upheaval and by the intrusion of melted rock, which has bent, broken, and twisted previously-existing formations in a most extraordinary manner, the results of which are well seen in the picturesque scenery of the Start, Prawle Point, and Bolt Head. Lundy, which is twelve miles from the nearest point of Devonshire mainland, is all granite, except for a small part of its south end, which is Millstone Grit.