product of the crusher
falls directly into the rotary screen, which revolves on an inclined
axis and empties the separate pieces into small bins below the crusher.
A better form for many purposes includes a larger and more elaborate
outfit, in which the stone is carried by an elevator to the screen and
by the screen emptied into separate bins according to the respective
sizes. From the bins it is easily loaded into wagons or spreading carts
and hauled to any desired point along the line of the road.

"The size to which stone should be broken depends upon the quality of
the stone, the amount of traffic to which the road will be subjected,
and to some extent upon the manner in which the stone is put in place.
If a hard, tough stone is employed it may be broken into rough cubes or
pieces of about one and a half inches in largest face dimensions, and
when broken to such a size the product of the crusher may generally be
used to good advantage without the trouble of screening, since dust
'tailings' and fine stuff do not accumulate in large quantities in the
breaking of the tougher stone.

"If only moderate traffic is to be provided for, the harder limestones
may be broken so the pieces will pass through a two-inch ring, though
sizes running from two and a quarter to two and a half inches will
insure a more durable roadway, and if a steam roller is used in
compacting the metal it will be brought to a smooth surface without much
trouble. As a rule, it may be said that to adhere closely to a size
running from two and a quarter to two and a half inches in largest face
dimensions, and to use care in excluding too large a proportion of
small stuff as well as all pieces of excessive size, will insure a
satisfactory and durable macadam road."

Macadam insisted that no large stone should ever be employed in
road-making, and, indeed, most modern road builders practice his
principle that "small angular fragments are the cardinal requirements."
As a general rule it has been stated that no stone larger than a walnut
should be used for the surfacing of roads.

Stone roads are built in most cases according to the principles laid
down by John L. Macadam, while some are built by the methods advocated
by Telford. The most important difference between these two principles
of construction relates to the propriety or necessity of a paved
foundation beneath the crust of broken stone. Telford advocated this
principle, while Macadam strongly de