342 
MliNING GEOLOGY 
way construction for a distance of at least as great as that from 
the nearest railroad station (a source of rail-hauled material). 
The quantity and quality of material available are reported upon 
in considerable detail. For concrete pavements this involves 
screen analyses, as well as silt and colorimetric tests, of all gravel 
and sand deposits both developed and undeveloped. Quarries 
and rock-outcrops, as potential sources of crushed rock, are 
given detailed study. One division engineer reported that such a 
survey saved the county $30,000.00 on one project alone. In this 
case the saving was entirely due to reduction in cost of truck haul. 
For surfacing, a search is made for all available material, 
whether this be gravel, shale, limestone, granite, clay, or sand. 
Not only are all available exposures examined, but in the case 
of undeveloped deposits, test-pits are dug. After elimination of 
all but a few of the more desirable deposits, the engineer carries 
on more extensive exploration of these before determining which 
particular deposit should be developed. Mapping on a more 
detailed scale than is possible on published maps is necessary as 
an area too small to appear on such a map may be underlaid by 
sufficient material for a large project. 
This work of course requires geologists of considerable field 
experience, since it involves not merely the making of geological 
observations, such as would be necessary in a glaciated region 
to distinguish terminal moraine, ground moraine and outwash. 
He must determine in what particular knoll of the terminal mor¬ 
aine, or in what small tract of the outwash plain, will be found 
the best kind of road material. This might be accomplished by 
tedious and expensive test-pitting over a whole outwash plain, 
for example, but a properly qualified geologist through his knowl¬ 
edge of the minute details of glacial geology should be able to 
eliminate large areas from consideration, and concentrate his 
efforts on the most favorable ones. In the study of an esker, 
instead of having to make test-pits throughout its length, the 
geologist should be able to select at a glance the places most 
likely to yield that particular kind of material needed for the 
project under consideration. In the area of glacial Lake Wis¬ 
consin, the soils are generally sandy. A search is made for places 
where the underlying lake clays are under only a thin sand¬ 
covering. Such a search involves a careful study of topography 
