Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne 1838 Vol.2.djvu/317

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