May 3, 1912] 
stance of the first inaccuracy the coastal 
plain is put on a par with the soils of gla- 
cial formation, however justified this may 
seem to be from the point of view of agri- 
cultural prominence. In the same line is 
the correlation of material occurring in 
the Ohio River bottom in Mason County, 
Kentucky, with the Norfolk series which is 
a part of the coastal plain. (Since 
changed.) The most serious errors in 
drawing the boundaries of individual types 
result from failure to appreciate the fac- 
tors upon which the larger separations are 
made. These difficulties are pointed out, 
not to minimize the value of the work done, 
for they weigh lightly against the large 
and fundamental value of the surveys 
which have been completed, and which in 
the main are sound, but rather with the 
purpose to illustrate the importance of 
stating as clearly as possible the factors 
which are used in the practical classifica- 
tion of soils and the comparison of these 
with what may be termed an ideal scheme 
of classification. It is objected by some 
persons that it is not possible to devise a 
perfect scheme which is applicable under 
all conditions. The important point is 
rather that we now have a fair understand- 
ing of the primary factors which produce 
agricultural differences in soil and that the 
use of these in the classification, represen- 
tation and study of soils is of great prac- 
tical value. We shall attain nearer a per- 
fect system as we accumulate more infor- 
mation on the subject. All of the elements 
of soil separation which are mentioned in 
the following pages have been employed in 
the work of the Bureau of Soils, but they 
have not been given equal or uniform 
value. 
The most comprehensive review of the 
methods which have been used in the classi- 
fication of soils is that by Coffey prepared 
as a thesis for the doctor’s degree in George 
SCIENCE 
681 
Washington University under the direction 
of Dr. George P. Merrill. 
The aim of this paper is to organize the 
factors which have been used in the classi- 
fication of soils and any others which ap- 
pear to have a controlling influence on the 
agricultural value of soil into a scheme 
which shall point out the fundamental fac- 
tors involved, and the relation of these 
factors to the distribution of soils in the 
field. The requisites and some of the lim- 
itations of such a scheme have been stated. 
It was noted that the crop-producing power 
of a soil is dependent upon its chemical and 
physical properties and the climate. 
Statement of Plan of Classification— 
The climate of a soil has two phases: First, 
the climate of the region in general, due to 
its geographic position. Second, the eli- 
matic conditions within the soil, due to the 
physical and chemical properties of the 
soil itself. Due to the latter two soils of 
different properties situated under the 
same general climatic conditions may pre- 
sent different climatic conditions to the 
plants growing upon them. The tempera- 
ture and humidity of sand and clay may 
be very different, which is illustrated by 
the fact that one is termed an ‘‘early”’ soil 
and the other a ‘‘late’’ soil. 
The physical and chemical properties of 
a soil are due to its mode of formation and 
the kind of materials used. The first in- 
elude the time element or extent of opera- 
tion of the processes and changes subse- 
quent to the general formation of the ma- 
terial such as drainage, climate, ete. The 
second include the kind of rocks from 
which the soil material is derived and may 
be as diverse as the kinds of rock multi- 
plied into the proportionate mixture of any 
combination of these. The scheme is, there- 
fore, genetic and in its broader lines purely 
geological. The relation of these to agri- 
