Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/124

106 flows sluggishly with many windings through the level country past Bradbury and Darlington to Blackwell. Still further east there is a stream similar in character but shorter and smaller, which from Sedgefield runs south-eastward to Norton and Billingham. Between Hartlepool and Sedgefield the level scarcely anywhere exceeds 100 feet, and southward it falls still lower. The streams and ponds of this level low-lying tract furnish the best stations for water-plants which there are in the two counties, as for instance, Morden Carrs, through which the railway runs between Bradbury and Aycliffe Stations, and the streams and ditches about Norton and Billingham. From the Tees mouth at Seaton Carew northward to Hartlepool there is very little cliff along the shore, but from this latter point northward the Magnesian Limestone borders it with fine cliffs in several places, especially at the Black Hall Rocks, and from Horden Dene northward the rocky wall is carried forward almost without interruption. We have regarded the denes of the Magnesian Limestone from Hawthorn Dene southward as comprised in this drainage tract. The most considerable of these is Castle Eden Dene, a thickly-wooded picturesque craggy ravine which extends from the shore midway between Hartlepool and Sunderland for a distance of five miles due west into the heart of the Magnesian Limestone range. The hills round the upper part are from 400 to 500 feet above sea-level. Hesleden Dene, a similar glen a short distance to the south, is about the same length but narrower. Hawthorn and Horden Denes, nearer Sunderland, are both much smaller and shorter. The area of the district is about 300 square miles.