26 THE HABITAT 
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 
15-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. Soil 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 cf 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 
Fig.2, Fraenkel COTE at different depths. Frequently, indeed, a ; 
“soil borer. a hand trowel may be readily used to obtain ee on onan 
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 _ 
