LIMESTONES. 317 



When the beds are horizontal or nearly so a stream gorge or road 

 cut may furnish a good idea of the character of the different beds. In 

 default of such an exposure, it will be necessary to sink test pits to 

 the rock, unless it is exposed conveniently at the surface, and then 

 secure samples from various depths by drilling. Whenever possible 

 the diamond-drill is the most satisfactory exploring device, for it is 

 practically an automatic sampler. 



When the beds are steeply inclined, a trench cut across at right 

 angles to the bedding will expose a series of beds and enable each to 

 be sampled. 



If the beds are horizontal or nearly so, and the various samples- 

 show little difference in composition, such a preliminary examination 

 as is described above may be all that is required. In case the rock- 

 beds dip at high angles, or if folds or faults are suspected, it will be 

 safest to call in a geologist or mining engineer as associate. If the 

 analyses disagree markedly, it will be advisable to undertake a more 

 detailed examination of the area. 



Detailed Mapping and Sampling. A much more detailed examina- 

 tion is always desirable before the actual erection of the plant is com- 

 menced. Such an examination will decide the best possible location 

 for the quarry, and should also give -data which will aid in keeping a 

 uniform mix. 



For these purposes a contour map, with 1-, 5-, or 10-foot contours, 

 according to the slope, on a scale of 25 feet to the inch, should be care- 

 fully prepared. The area to be examined should be laid out in 25- or 

 50-foot squares and their corners marked and numbered to correspond 

 to their locations on the map. At least three good points should be 

 selected as permanent bench-marks, far enough away from the pros- 

 pective quarry-site as not to be disturbed by excavation or blasting, 

 and the locations and elevations of these points should be carefully 

 determined and placed on the map. 



Sampling should now be taken up carefully. For final work this 

 can be done satisfactorily only with the diamond drill. Drill-holes 

 should be put down at every corner of the 50-foot squares. Each 5 

 feet of the core should be sampled and analyzed separately, to a depth 

 of at least 50 feet. If the rock dips steeply, or if for any other reason 

 a deep, narrow quarry seems probable, the drilling should be continued 

 to 200 feet. If the cores from adjacent bore-holes give closely similar 

 analyses, closer drilling is not necessary. But if two samples taken 

 at the same depth from two adjoining holes show differences of more 

 than 3 per cent in their lime carbonate, or more than 1| per cent in. 



