Projection to Geological Plans and Sections. 283 



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 Lime- 

 stone 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. 



