Mr. T. Sopwith, on Isometrical Projection. 277 



No. XII. — On the Application of Isometrical Projection to Geological Plans and 

 Sections ; with descriptive Notices of the Mining District at Nentsberry, in 

 the County of Cumberland. By T. Sopwith, F. G. S. 



Read May 21, 1832. 



Jn pursuing geological researches, and especially such as relate to the 

 stratification of important mineral districts, the aid of drawings, plans, and 

 sections, is indispensable. The ablest pen is inadequate to the description 

 of many objects and circumstances which it is highly important should be 

 known, but which the drawings of the artist, or the plans of the engineer, 

 at once present in a clear and definite manner. 



Such being the value of correct delineations of geological phenomena, 

 whatever tends to render such drawings more applicable to scientific pur- 

 poses, or more generally intelligible, is especially deserving the attention of 

 a society so interested as this is, in the Geology and Mining of the North 

 of England, and which derives so much illustration from the plans and 

 sections annexed to many of the papers in its transactions. 



Horizontal and vertical plans and drawings are so commonly used as to 

 be generally well understood. In both these modes of projection the eye 

 is supposed to be at an infinite distance, so that no one part of the surface 

 represented appears less than another, which would be the case if the point 

 of view was considered as being in any finite distance, however great. The 

 horizontal plan and vertical section afford a correct idea of the respective 

 planes which they represent, but they comprehend such objects only as are 

 exactly upon each plane, or parallel to it. Whatever deviates from that 

 plane either cannot be shown at all, or must be more or less distorted. 



These two planes are shown in the Plan of Holyfield Mine, Plate XIII., 

 and it will be seen that the Section comprising one vertical plane only, 

 viz., that above the Holyfield Sun Vein, does not include the northern 



VOL. II. 3 K 



