SEARCHING TOR MARL. 305 



obtained the best possible indications of the probable existence of 

 the same bed in a more desirable situation. As the beds usually 

 lie nearly horizontal, and are continuous for considerable distances, 

 the search should Jbe extended upon nearly the same level. . Natural 

 exposures may have been made by the courses of rivers or smaller 

 streams or artificial, by the digging of ditches, wells, or other 

 excavations. If none of these serve to expose marl to view, the 

 next resort will be to boring. And in using the auger, the same 

 rule should be pursued of being guided by the supposed level of 

 the bed sought. Of course, any nearly horizontal lower bed will 

 have the least covering of upper earth where the surface is most de- 

 pressed. Thus, under swamps, or in deep bottoms or ravines, a hidden 

 bed of marl may be expected to be reached with less depth of boring 

 than on the higher land. But it will not do to rely upon borings 

 in these lowest depressions only. For in many cases, the marl 

 itself, or the upper part of the bed, has been washed away and re- 

 moved by the ancient action of running water, and the cavity sub- 

 sequently filled by other washings of earth, forming the present 

 surface soil and lower layers. Therefore, besides boring in the 

 lowest ground, the nearest rise of the adjacent slope of high land 

 should be tried. There the marl would have been left, even though 

 removed in the former lower channel of the ancient strong current 

 of water. 



If marl reaches the surface, or is cut into anywhere by the wash- 

 ing of rapid streams, it may probably be found by examining the 

 deepest parts of these cuttings. Any of the smallest particles of 

 shells found in the lower part of the course of the stream will 

 clearly indicate that the water has cut into marl somewhere above; 

 and which place may be found by carefully examining the bed of 

 the stream above. 



The auger most convenient for the ordinary searching for marl 

 is a very simple and cheap implement. It is made by welding a 

 straight cylindrical iron rod, five-eighths of an inch in diameter, 

 to the stem of a common screw auger of about one and a half 

 inches bore. If the auger has been so much worn in use as a car- 

 penter's tool, as to be unfit for that work, it will serve well enough 

 for boring in earth. A cross-piece for a handle, also of iron, and 

 14 inches long, should be fitted to slide along the stem (which 

 passes through a hole in the handle), and small indentations are 

 made, two feet apart, on the stem, at which the handle is fixed, at 

 any desired height, by a small thumb-screw, passing through one 

 side of the handle, and the point pressing into the indentation on 

 the stem. The lowest indentation should be 4 feet from the lower 

 end of thfc auger, and the others at every 2 feet above. An 

 auger of 12 feet length will serve for all ordinary operations, 

 and is not too unhandy in use. But, it will be more convenient, 

 26* 



