Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/101

1436 feet in altitude. From this point down to Alwinton the distance is 14 miles. The most interesting point of the river is at Linn Shiels, 2 miles west of Alwinton. Here, on the east, a precipice of porphyritic crag rises from the stream to a height of 100 feet above it. The opposite bank is also steep and craggy, and a horse-shoe shaped ravine is formed, at the bottom of which the stream, pent within a narrow channel of rock, flows in a succession of leaps and dark peaty pools. This is the point at which, proceeding downwards, the sedimentary strata are first reached in the bed of the river; and below the ravine the Tuedian flagstones may be seen clearly dipping towards the south-east at a steep angle of inclination. The Ridlees Burn, which joins the Coquet just below, is almost coincident along its whole course with the line where the porphyry ceases. At Windyhaugh, 6 miles from its source, the Coquet is only 830 feet above sea-level, and at Alwinton, 8 miles lower down, it has sunk to 500 feet. In the corner between the Alwine and the Coquet, the hills rise to a height of about 1000 feet. The upper part of the Alwine has the same character as that of the Coquet, so that this drainage tract contains almost as much porphyritic hill and dale country as the first district, a tract of about 70 square miles in area, stretching from Alwinton away to the north and west, steep ridges and high rounded knolls with bare grassy banks, diversified but rarely by those same sweeps of grey or brick-red porphyritic rock of which we have already spoken, a monotonous and very lonely region, that seems to be given up almost entirely to the sheep. We have given already a list of the plants of one of the Alwinton cliffs, and must now take a final leave of the porphyritic region. Between Alwinton and Rothbury, on the north side of the river, the ground, stretching away from the Coquet towards the head of the Aln, is flat and cultivated, hardly anywhere exceeding 500 feet above sea-level. The lowness of this tract, when the stream lower down on the same side is bordered by high heathery moorland, seems anomalous to one accustomed to the gradually rising banks of hill that usually margin the streams that flow from the Pennine chain on the east. On the south side of the Coquet the physical