The Country round Lyell the Goal-Field 



sea. From Fig. 21 it will be seen that the depth of a 

 stratum in level country is determined by the distance 

 from the outcrop, measured in the direction of the 

 dip, multiplied by the tangent of the angle of dip. AB 

 is the distance from the outcrop, and BC is the depth 



Rr^ 



of the stratum at B, and -^-g is the tangent of the angle 

 BAG. 



= tan.BAC. - 



BC = ABxtan. BAG. 



From this it follows that the farther we go to the south 

 the greater will be tin ;" depth of the base of the Permian. 

 For this reason we 

 must choose a site 

 as near the outcrop 

 as is consistent with 

 our object of ex- 

 ploring as far to the 

 south as possible. 



On the whole, a 

 point in the valley 

 of the West River 

 could there obtain 



FIG. 21. 



would be most suitable, as we 

 the water necessary for the work, 

 and after looking over the ground we selected a point 

 marked B.H. No. 2 on the map. This lay exactly 

 2 miles south of the outcrop of the base of the Permian, 

 and was at an elevation of 750 feet above sea-level. 



The base of the Permian will fall in i mile, i 

 mile = 5280 feet x tan. 3. From a book of tables we 

 find that tan. 3 = 0*0524. The fall in feet per mile will 

 therefore be 5280 x 0*0524 = 276*6. 



127 



