92 Forest Club Annual 



In discussing the stratigraphy of a mining district, the 

 examiner should carefully consult the geological reports pub- 

 lished on that district before naming and describing the geolo- 

 gical formations represented. Rocks should be described under 

 the headings Sedimentary or Stratified, Metamorphic, and 

 Igneous. In making cross sections of the formations repre- 

 sented on a claim the various types of rock should be designated 

 by the symbols illustrated in figure 1. These symbols are 

 used in State and Federal Geological Survey reports. In a 

 preliminary report, a convenient method of showing the 

 character of the strata is to combine a photograph with ex- 

 planatory columnar section^ especially if the ore occurs in 

 bedded deposits. The method is illustrated in figure 2 show- 

 ing massive limestone interbedded with shales in a quarry 

 face. 



V. STRUCTURE 



1. Under the heading "structure", describe all intrusive forms, 

 giving the general characteristics of the rock mass. 



2. Discuss folding and faulting, giving numerous dip and strike 

 readings in describing the folds, and if faults occur the 

 amount and direction of displacement and the inclination of 

 the fault. 



It is always essential that the dip and strike of the 

 stratified rocks, coal beds, and mineral veins be given. Al- 

 though it is usually a simple matter to take such readings with 

 the compass, the inexperienced men in the work will have 

 some difficulty in taking and recording such data. 



The dip of a bed or vein has been defined as "the angle 

 of inclination which a tilted stratum makes with the plane of 

 the horizon" and is measured in degrees. "The direction of 

 the dip is the line of steepest inclination of the dipping bed." 

 Thus we may say a stratum or vein has a dip of 20 degrees to 

 the northeast. 



The angle of dip is measured with an instrument called 

 a clinometer. Most of the compasses used by foresters and 

 geologists are provided with clinometers. 



In measuring the dip of mineral veins and coal beds, one 

 should secure as many readings as possible in mines and pros- 

 pect holes in order to compensate the readings taken at the 

 surface which are frequently not the true dips, since the out- 

 crops are affected by terminal curvature (creep or slumping) 

 of the vein at the surface. 



