Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne 1838 Vol.2.djvu/320

280 downcast of the east side of the vein 19 fathoms, and Nentsberry Greens Cross Vein has a similar throw of 27 fathoms. By far the most important stratum of this district is the Great Lime- stone, the bassett of which, in this and several adjacent dales, forms the limit of cultivated land and of human habitations. It preserves a nearly uniform thickness of 9 or 10 fathoms, and has produced as much ore as all the other strata put together ; the Rampgill Vein having, in this Limestone alone, produced 400 tons of Lead ore in each fathom of length for a consider- able distance. It is from the Great Limestone also that the mineral riches of Hudgill-burn have been chiefly obtained. The Aqueduct of Nentforce Level is driven for three miles and a quarter under the bed of the River Nent, and may be navigated in boats to the shaft at Nentsberry represented in Plate XII* It was projected by the celebrated Smeaton when one of the receivers of Greenwich Hospital, in 1775, was commenced in the following year, has been regularly prose- cuted since that time, and is now being continued on the top of the Scar Limestone towards the important mining field of Nenthead, the extent originally proposed. The Scar Limestone is next in thickness to the Great Limestone, varying from 7 to 9 fathoms, but has been much less productive of Lead. It forms many romantic features in the scenery of Alston from its precipitous basset, especially at the waterfalls of Eshgill and Nentforce, the latter of which is only a few yards from the entrance of Nentforce Level. Having thus premised a few of the circumstances which attach geological and mining interest to the vale of Nent, it remains to offer some remarks on the application of Isometrical Projection to a plan of a portion of this dis- trict. The situation which I have selected for this purpose is an area of about a mile square at Nentsberry, midway between the source of the River Nent and the market town of Alston. It includes several of the objects alluded to, embracing the strata from above the Great Limestone down to the aqueduct of Nentforce Level, showing the shaft and higher level, the course of Old Carr's, or Nentsberry Greens Cross Vein, the great disruption of the strata, and the subterranean workings in the Great Limestone at Welgill Cross Vein, &c.