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CONSTRUCTION SOURCES OF GRAVEL, MINTZER 143 
situations support corn. Usually these crop types, when associated with each other, 
have specific positions of the terrain, ie. the wheat likes the higher elevated terrain KA 
while corn is found in the lower reaches. When these crops have been identified on a | 
given photo the soil conditions in these areas may then be inferred by the interpreter. | 
Land use. hi 
The features which have been placed on the face of the earth represent how the | 
human being adapts himself to his environment or to changes which suit his needs. If hil 
the ground is too dry for agricultural pursuits of one sort or another, man employs a 
method called dry farming, i.e., cultivating alternate sections each year, and alternating 
the use of parts of the terrain from year to year. In dry areas of the world, such as 
in India, man contour plows the fields to protect loose soil conditions from erosion. 
These plowed fields present regular plowed rows folling the hillside with a tiered effect | |] 
or even striped effect. In humid regions, if the ground is too wet, the farmer uses such MI 
features as dead furrows, field ditching, or tile to redistribute the excess moisture. In 
flat country the roads are usually placed alongside of fields, criss-crossing the country- 
side in regular intervals. Thus, rectangular field patterns usually indicate flat terrain. 
In the case of gravel terraces, or outwash plains, the rectangular pattern is a signifi- 
cant feature. Man, of course, opens quarries in such granular plains. One note worth 
mentioning is that the absence of ditching and tiling is generally observed in gravel 
plains or terraces. This characteristic is an excellent identifying feature when coupled 
with other elements of the pattern. 
Landforms which include gravel sources. 
Application of the areal concept method to locating gravel sources requires appro- 
priate knowledge of the geological origin of the ground surface. Since gravel sources are 
of immediate concern, this discussion gives certain ideas related to the ground patterns 
associated with sources of granular materials. Many landforms contain gravel but those 
of special interest herein are moraines, outwash plains and terraces. 
All terrain situations where a given granular composition of rocks and earth is con- 
cerned have one thing in common, i.e., the underlying material. This common gravelly 
soil gives the engineer, or the photo interpreter, an advantage. In general, gravel sources 
are associated with water or ice deposition, i.e., inland lakes, streams, terminal moraines 
or eskers and kettle-kame terrain. In general, running water was the active force which 
carried heavy to light particles in all sizes from coarse to fine. Depending upon the velo- 
city and changes in velocity, direction and flattening of gradient of the stream, the mate- 
rials were sorted out in accordance with the laws of sedimentation in the downstream 
direction. The carrying capacity of the stream may have varied in magnitude from that 
of a small hill-gully carrying and depositing clay and small pebbles, to the tremendous 
stream of glacial melt waters, many miles in width, flowing outward from beneath a 
mass of ice many thousands of feet in thickness. In the latter, boulders weighing a ton IM 
or two may have been moved by the stream flow. Likewise, the slow flat gradient stream IM | 
may generally have only the very lightest clay-size particles. IM 
The ground forms associated with lakes are usually flat, gently sloping beaches, or 
beach ridges of early ice origin. Sometimes these forms may be situated some distance 
from the present lake shore as in the case of the glacial lakes of extint character like 
Lake Aggasiss. 
The granular deposits associated with streams are found in a topographic situation 
above the level of the present stream bed, forming elevated benches or terraces. Where 
terraces are associated with streams, the interpreter visualizes the physical geographic 
position of the terrace. Towards the upstream positions of the headwaters the coarser 
materials may be found. The proximity of the stream head, say a few miles away, often