MEASUREMENT OF THE " DIP." 21 



crop," and where the surface is level the direction of course 

 can be measured by the " strike." 



In measuring the dip of a bed, or lode, or slope of a hill, 

 the eye can be of great service in doing so approximately ; 

 but an instrument called the clinometer is of more use when 

 accuracy is required. Various kinds of this simple instru- 

 ment are to be met with, some having a prismatic compass 

 and a spirit level in the same apparatus; the principle, 



FIG. 16. CRYSTALLIZED MINEBAL LODE. 



a or, on each side of the lode, is a band of iron pyrites. 



b b represents plates of quartz upon the iron pyrites. 



c c are copper pyrites the yellow sulphide of copper and iron. 



d d are bands of quartz and fluor spar. 



e e are bands of quartz containing veins of copper ore. 



ff are crystalline layers of quartz, with strings of copper ore. 



however, is the same in each. A very simple one can be 

 easily made as follows. On a rectangular piece of wood or 

 cardboard describe a semicircle as in Fig. 17. From c, the 

 centre of the whole circle, draw c D at right angles to A B. 

 Divide A D into 90, and D B into 90, placing the zero mark 

 at D, and the divisions 10, 20, .... 90, as in the illustra- 

 tion. Let a plumb-line, such as a piece of thread with a 

 small weight at the lower end, be suspended from a nail or 

 small pin at C. 



