282 Mr. T. Sopjvith, on the Application of Isometrical 



neated so as to exhibit its depth, and the several strata sunk through, as 

 at Fig. 6, Plate XIII. The levels of Holyfield Vein and Holyfield Sun 

 Vein, which, on a common ground plan, appear on one plane, may be shown in 

 their proper situations, one above and the other below, the stratum of Lime- 

 stone in which the mine is principally wrought. Such parts of the surface as 

 have been correctly levelled can be exactly delineated, and whatever acces- 

 sions of this kind are gained can at any time be added on an Isometrical Plan. 

 Hence, if it is desired to sink a shaft, or drive a level to meet other workings 

 a clear and intelligible record of the relative positions required is at hand, 

 supplying the place of a numerous and unconnected series of Plans and Sec- 

 tions. True it is that when the parts of a mine become very numerous and 

 complicated, the Isometrical Plan will appear so likewise, but this is an imper- 

 fection common to all plans, though certainly not so much to those which 

 include only one plane, instead of a number of planes in all directions. 



From what is here said, it must not be supposed that the advantages of 

 this perspective are such as to supersede the use of other plans ; on the 

 contrary, it must be kept in mind that the common ground plan and ver- 

 tical section are among the very clearest and most perfect aids which 

 drawing can afford to science : the application of one common scale in 

 every direction of them renders them so easily understood, and so much 

 within the reach of even the most ordinary understanding, that no other 

 kind of projection can excel them as a popular and useful mode of 

 delineating subterranean features. But as an auxiliary to these, and as 

 possessing peculiar advantages, Isometrical Projection claims a share of 

 attention, and may be employed with success in a variety of instances. Its 

 minuter details require an eye and hand more intimately familiar with the 

 principles of its projection than ordinary plans, but its general features are 

 easily understood. Those who are at all accustomed to geological plans 

 will have little difficulty in understanding the example given in the Plan of 

 the mining district at Nentsberry Greens, Plate XII* The surface, with its 

 walls, fields, roads and houses appears as if viewed obliquely from a great dis- 

 tance, and where the surface is supposed to be removed, a view of the strata 

 is afforded in numerous vertical sections. By a perpendicular line the thick- 

 ness of the strata can be measured by the same scale in any part of the 





