26 



THE HABITAT 



X 



has a removable rod, flattened into a disk at one end, and bent at the other, 

 for forcing-out the core after it has been cut from the soil. Sets of geotomes 

 have been made in lengths of 5, 10, 12, 15, 20, and 25 inches. The 12- and 

 1 5 -inch forms have been commonly used for herbaceous formations and 

 layers. They are marked in inches so that a sample of any lesser depth may 

 be readily taken. Such a device is very necessary for gravel soils and in 

 mountain regions, where the subsoil of rock lies close to the surface. 



42. 5oil borers. There is a large variety of soil borers to choose from, 

 but none have been found as simple and satisfactory for relatively shallow 

 readings as the geotome just described. For deep-rooted plants, many 

 xerophytes, shrubs, and trees, borers of the -auger type are necessary. 

 These are large and heavy, and of necessity slow in operation. They can 

 not well be carried in an ordinary outfit of instruments, and the size of the 



soil sample itself precludes the use of such 

 instruments far from the base station, except 

 on trips made expressly for obtaining samples 

 from deep-seated layers. For depths from 

 two to eight feet, the Fraenkel borer is per- 

 haps the most satisfactory, except for the 

 coarser gravels; it costs $14 -or $20 according 

 to the length. For greater depths, or when 

 a larger core is desirable, the Bausch & Lomb 

 borer, number 16536, which costs $5.25, 

 should be made use of. This is a ponderous 

 affair and can be employed only on special 

 occasions. On account of the size of samples 

 obtained by these borers, it is usually most 

 satisfactory to take a small sample from the 

 core at different depths. Frequently, indeed, 

 a hand trowel may be readily used to obtain 

 a good sample at a particular depth. 



43. Taking samples of soil. In obtaining soil samples, the usual practice 

 is to remove the air-dried surface, noting its depth, and to sink the geotome 

 with a slow, gentle, boring movement, in order to avoid packing the soil. 

 This difficulty is further obviated by deep notches with sharp, beveled edges 

 which are cut at the lower end. In obtaining a fifteen-inch core, there is 

 also less compression if it be cut five inches at a time. Repeated tests have 

 shown, however, that the single compressed sample is practically as trust- 

 worthy as the one made in sections. The water-content of the former 

 constantly fell within .5 per cent of that of the latter, and both varied less 



Fig. 2. Fraenkel 

 soil borer. 



Fig. 3. Ameri- 

 can soil borer. 



