Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne 1838 Vol.2.djvu/323

Rh plan, and the perpendicular direction is easily ascertained by means of the angles of the Isometrical Squares.

Near the left hand corner at the bottom of the plan, is Nentsberry engine house and shaft, with adjacent cottages. The shaft is nearly 60 fathoms in depth, and the several strata intersected by it are delineated on the plan. The shaft communicates with the aquaduct of Nentforce Level, which here terminates, at a distance of three miles and a quarter from its entrance at Nentforce, near Alston.

In order to measure the relative height of objects represented on the plan, some fixed horizontal plane must be assumed, and, in the present instance, a plane coinciding with the base of the level mouth of Nentsberry Greens Level is adopted. This plane may be familiarly compared to what would be formed if an immense horizontal plane was inserted in the earth so as to extend over and define every part of the district which is on the same plane or level with the base of Nentsberry Greens Level mouth. On this plane, squares are drawn for convenient reference, the sides of which may form meridian, and east and west lines.

At the distance of 61 fathoms below this plane, a horizontal line is drawn and above it are represented the various strata, together with the line of surface. The continuation of Nentforce Level on the top of the Scar Limestone is also shown.

The south limit of the plan is marked by the termination of the squares on the right hand side of the drawing, and coinciding with this boundary is another section, having for its base a line 61 fathoms below the horizontal plane. Here the strata are seen rapidly rising towards Old Carr's Cross Vein, by which they are thrown down 25 fathoms. The strata then continue level (which is shown by their parallelism with the horizontal base line), until they approach Wellgill Cross Vein, they then rise rapidly towards it, and on the other side of the vein are thrown up about three fathoms.

The Section in the middle of the drawing exhibits the adit or level of Nentsberry Greens Mine, which, by the throw of Old Carr's Vein, suddenly passes from a soft argillaceous bed into a solid mass of Limestone. The upper section exhibits the subterranean workings of Wellgill Cross Vein Mine.