Outline for Preliminary Report on Mineral Claims 95 



VI. MEASURING INCLINED STRATA 



It is a simple matter to measure the thickness of a forma- 

 tion or a bedded deposit such as a coal vein or a brick shale, 

 if the strata are in a horizontal or vertical position. Horizontal 

 beds are inconvenient to measure only when covered with 

 debris or talus. Usually, however, horizontal strata are suf- 

 ficiently well exposed along valley and canyon walls to secure 

 measurements without resorting to boring to determine the 

 thickness. If the strata are vertical the beds are practically 

 uninfluenced by the form of the surface and the outcrop is the 

 true thickness of the strata. It is obvious that a line measured 

 across the strike of an exposure of vertical beds gives the 

 exact thickness. Most sedimentary formations have been 

 tilted at angles of greater or lesser degree and the thickness 

 of inclined beds must be computed from the width of the 



Fig. 8. Diagram to illustrate how the thickness of a stratum may be 

 determined from the angle of dip and the width of the surface expos- 

 ure. Width of outcrop multiplied by the sine of the angle of dip 

 gives the true width of stratum (after Hobbs). 



exposure and the angle of dip ; or graphically estimated by il- 

 lustrating the width of surface exposure and the inclination of 

 strata, after which it is a simple matter to draw a line at right 

 angles to the dip from the base to the top of the formation 

 and scale the thickness. 



When obtained by computation, with the width of ex- 

 posure and angle of dip given, the exposure width is multiplied 

 by the sine of the angle of dip. 



