96 Forest Club Annual 



Charles Maclaren in his Geology of Fife and the Lothians, 

 gives the following rule for estimating the thickness of a 

 formation in the field : 



"If the breadth of inclined strata be measured across their 

 outcrop, at right angles to the strike, their true thickness will 

 be equal to one-twelfth of their apparent thickness for every 5 

 degrees of inclination." Or the rule may be stated thus : 

 Divide 60 by the dip, and you obtain the fraction which ex- 

 presses the thickness. Thus suppose a series of strata meas- 

 ures across the strike 1200 feet if the dip of the beds be 5 

 degrees their thickness is one-twelfth, or 100 feet; if the dip 

 be 10 degrees the thickness is one-sixth, or 200 feet; with a 

 dip of 15 degrees we get a thickness of one-fourth, or 300 feet; 

 and a thickness of one-third, or 400 feet, when the dip is 20 

 degrees. The rule is sufficiently correct for field purposes up 

 to an inclination of 45 degrees. 



Figure 8 illustrates the method of computing thickness 

 from the width of exposure and the angle of dip. 



VII. ORE BODIES 



1. If the ore bodies occur as veins, give: 



a. Width, maximum and average. 



b. Character of the ore or vein filling. 



c. Character of walls or country rock. 



d. Throw or displacement of walls, if any. 



e. Dip and strike of vein. 



f. Location of apex of vein. 



g. Character of ore at outcrop and below the surface. 



2. If the vein or ore body contains "horses," lenticular masses 

 of ore surrounded by country rock, or large concretionary 

 masses of foreign mineral and rock substances, give : 



a. Number, size, location, and material. 



b. Name the gangue minerals. 



3. If the ore occurs as beds or lenses, give: 



a. Number and regularity of lenses. 



b. Character of walls, dip, and strike. 



c. Shape, and size (always giving maximum and average 

 width). 



The width of a vein or bedded deposit at the outcrop 

 is not always the true width, being affected by the inclination 

 of the vein, strata or interbedded deposit, and by the ground 

 plan or topography. When the strata are inclined the outcrop 

 will be broad if the dip is low, and narrow if high. If the 



