Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/105
coarse grained variety of this rock, closely allied to the porphyry, and the perpendicular cliffs of Hellhole on the opposite side of the Cheviot consist also of the same rock.
The only metallic ores known to exist in this district are, bog iron-ore, which is found in the bottoms of morasses, and red ochre with nodules of hematite from a small vein traversing the rocks above Langley-ford. The shepherds use the latter for marking their sheep.
Blocks or detached masses of different rocks are found scattered over the surface of all the preceding formations and imbedded in the soil.
Masses of blue coralloid limestone, the produce of the lead-mine district, are found at the surface at Cullercoats above the magnesian limestone. Similar blocks are found dispersed over the other formations.
Masses of close-grained sandstone occur every where in like manner.
Masses of hard black basalt are found every where in abundance. From this stone the ancient inhabitants of Britain formed the heads of their battle-axes, which the people call Celts. They resemble in shape the tomahawks brought from the South Sea islands. Barbed arrow heads, neatly finished, and made of pale-coloured flint, are frequently picked up on the moors, and are called elf-bolts.
Masses of porphyry, resembling that of Cheviot, and of the Cumberland mountains, and of green basaltic porphyry are common. The base of the latter is of a greenish black colour, and contains