52 
FLORIDA GEOLOGICAL SURVEY. 
roughly determined by ascertaining the amount of water 
necessary to fill the interstices of the sand. A simple 
procedure recommended in Farmer’s Bulletin No. 311, U. 
S. Department of Agriculture, p. 10, is as follows: ‘‘Two 
ordinary glass tumblers of the same size are filled to the 
brim, one with dry sand to be tested and the other with 
water. The water is then poured carefully from the one 
glass into the sand in the other until it reaches the point 
of overflowing. The volume of water removed from the 
glass which was originally full of water can be taken as 
an approximate measure of the voids in the unit volume 
of sand contained in the tumbler. A simple calculation 
will reduce this to percentage volume.” 
Since all clay contains more or less sand, it may be 
expected that certain localities will supply clay that con¬ 
tains the right admixture of sand and clay to form a 
natural sand-clay road, or so nearly the proper admixture 
that it will serve that purpose satisfactorily. Fortunately 
for Florida, almost every county is supplied with an 
abundance of clay which serves admirably the purpose 
of road-making. The widespread occurrence of sandy 
clays in the north, west and central Florida has already 
been mentioned. The clay in many of these deposits con¬ 
tains sand and clay so proportioned as to make excellent 
roads. With this material at hand road construction in 
country sections is carried on at a minimum expense, and 
the resulting roads, while not all that could be desired, 
are a great improvement over the ordinary sand roads. 
They find their greatest usefulness in country sections 
where cheapness in road-making is necessary. Their spe¬ 
cial usefulness arises from the fact that owing to their 
widespread occurrence they can often be obtained from 
pits near at hand, thus lessening the expense of transpor¬ 
tation. Many of these clays have the disadvantage of being 
sticky after rains. In the open country, however, where 
these roads find their greatest usefulness a part only of 
the road is clayed, the remainder of the road remaining 
sandy is traveled during seasons of rain, at which time 
