FIELD GEOLOGY. 



Note. The particulars of the coal shaft when drawn 

 to scale, and with the beds assigned to their 

 proper formations, constitute what is called 

 a " Vertical Section" (fig. 23). 



By drawing the section (fig. 22) at the surface, from all 

 the dips and particulars obtained, then inserting the data 

 from the coal-shaft in their proper position (with the 

 dips reduced for deviation of the line), we have no 

 difficulty in correlating the beds and uniting the ascer- 

 tained points in their planes of stratification. The coal- 

 seam which comes to the surface where the section 

 crosses the fault is thus shown to be the "Thin-coal " at 

 1080 feet; the one above it, at 800, is doubtless the 

 seam that crops out on the E. side of the area. 



Eruptive Rocks. The rock of different character met 

 with in traversing the Coal-measures area, p. 208, was first 

 seen in a wall-like terrace running in a N.W. direction ; 

 all its outer surface was weathered almost to whiteness. 

 With some trouble a specimen is detached which shows 

 the rock beneath the weathering ; this is grey in colour, 

 does not effervesce under acid, and can be scratched by 

 a knife with difficulty, therefore it consists of silicates. 

 It is compact in texture, even in fracture, and has a 

 vitreous lustre ; it is probably Felstone, and the mass is 

 either eruptive or intrusive. 



There is no difficulty in mapping the mass, as it 

 makes quite a feature standing out from the softer and 

 more easily-denuded Coal-measures ; on one side only 

 are there recent accumulations of rain-wash, but by 

 these the feature is not obliterated. The rock proves 



