F. B. GUTHRIE. LIX. 
amount, and the very striking peculiarity has been pointed 
out by Hilgard that the humus in arid regions is very much 
richer in nitrogen than is the case with the humus in moist 
regions. So much is this the case that the nitrogen in the 
humus in arid regions rises as high as 15 per cent., or about 
three times the amount present in the humus of humid 
regions, which is about 5 per cent. 
Powdery condition of the soil when dry.—A third strik- 
ing characteristic of these soils, and one not shown in the 
tables, is their peculiar powdery condition when dry. 
Everybody who has been in the districts referred to is aware 
that the surface soil over large areas is carried away by 
the wind in the form of a fine dust, which is deposited 
against outstanding obstacles, or, if unobstructed, is carried 
enormous distances, to be ultimately deposited when the 
wind subsides, or carried down in the form of mud by a 
shower of rain. This phenomenon is noticeable in all arid 
regions, and Hilgard attributes it to the larger content of 
lime which these soils contain. It is well known that the 
addition of lime to clay renders the clay pulverulent and 
incoherent on drying. There are, however, reasons which 
make it difficult to accept this as a complete explanation 
of the cause of the incoherent nature of our soils. In the 
first place the quantity of lime, though larger than in the 
case of the soils from the more humid parts of the State, 
is not by any means excessive, and it is only exceptionally 
that they contain as much as is found in the average of the 
soils examined by Hilgard. In connection with this matter, 
Mr. Cohen has made some experiments in our laboratory 
in regard to the behaviour on drying of clay soils mixed 
with different quantities of lime. He finds that a clay soil 
containing °53 per cent. lime (an amount above the average 
in our soils) when moistened and subsequently dried, became 
quite hard—as hard as clay which contained no lime—and 
