316 CEMENTS, LIMES, AND PLASTERS. 



the work that has been done by geologists in the areas under consider- 

 ation. Most States now have geological surveys, and there are few 

 important limestone deposits that have not been located and examined 

 by these organizations or by the Federal survey. Numerous reports * 

 on these subjects have been issued by State or Federal Geological Sur- 

 veys, and these reports can usually be obtained free or at a merely 

 nominal price on application to the proper officials. If such a 

 report can be obtained covering the area to be examined it will do 

 away with a lot of preliminary work on the part of the prospector or 

 engineer. 



Preliminary Examination. In commencing work, it is desirable 

 to prepare a rough map of the area. For this purpose high accuracy 

 is not required, and a pocket compass or Brunton compass, with a Locke 

 level, and a small protractor will be the only instruments required. 

 With these a map can be made and plotted on a scale of 50 or 100 feet 

 to. the inch, distances being measured by pacing. The location of any 

 natural outcrop, pits, wells, road or railroad cuts, and streams should 

 be shown on the map, and their relative elevations ascertained as exactly 

 as possible. When the rocks are lying almost horizontally, the loca- 

 tions of the outcrops are of far less importance than their elevations. 



If there are sufficient good exposures of the rock, in either natural 

 or artificial cuts, samples should be collected from these outcrops. The 

 weathered part of the rock should be rejected, care being taken that 

 the samples represent the fresh, undecomposed rock. When the natural 

 exposures are not satisfactory, it will be necessary to secure samples 

 by trenches, pits, or boring. 



Most of the limestones with which the cement manufacturer may 

 have to deal occur in beds or layers which are practically horizontal 

 In the Appalachian and other disturbed districts, however, the beds, 

 may be tilted to a considerable angle with the horizontal, and in rare 

 cases they may even be almost vertical. Usually samples from differ- 

 ent parts of the same bed (within reasonable distances of each other) 

 will be very similar in composition; but, on the contrary, two adjoin- 

 ing beds may differ greatly from each other. 



In sampling, therefore, it is desirable to collect at least one speci- 

 men from each bed or layer, noting the thickness and position of the 

 bed. Even thin beds should not be neglected, for a 4-inch layer of 

 highly magnesian rock might prove a serious drawback to the eco- 

 nomical working of the quarry if its presence were unsuspected. 



* See reference lists on pp. 92-94. 



