Naturally mixed bank sand and gravel are sometimes found in the right
proportions for making concrete. Generally, however, there is far too
much sand for the gravel, and great care should be exercised in using
this class of material. Unless the mixture runs very even throughout
the bank, and is found to be made up of one part sand to two parts
gravel, it is better to screen the sand out of the gravel and prepare
the materials in the usual way.
Herewith is a table showing the quantities for a natural mixture of
bank sand and gravel. The quantities can be found in the same way as in
Table I, on page 11.