142 CONSTRUCTION SOURCES OF GRAVEL, MINTZER 
provision has not been made. A highly integrated drainage system with branching tribu- 
taries presents a photo image which can be used to infer poor internal drainage charac- 
teristics. 
Porous materials, like sand and gravel, tend to absorb the moisture. The run-off is 
less effective as an eroding force. Thus drainage systems are less developed. Rivers rushing 
across vast plains of gravel generally disappear beneath the surface. In gravel terraces 
broad systems do not exist, but where soils are less porous infiltration basis tend to 
show up. 
Erosional features. 
Erosion, nature’s mode of transfiguration of the earth’s surface, gives a direct clue 
to the soil texture and profile features. There are three general gully forms; each one 
has been found to be associated with a major soil textural group. The granular have the 
V shape and loessial soils and sand-clays have the U form or modified U; whereas clays 
and silts or combinations thereof have the broad dish or saucer form. 
In some instances the erosional features also reflect the flash type rainfall charac- 
teristic. Areas subjected to erosion from flash type rainfall become bad lands with sharp 
rugged features. 
Soil textures and details of the soil profiles can be partly predicted from the photo 
images of the above described erosional features. The erosional features important in 
prediction of soil types are the gully forms and their gradients. Dense woods obscure 
some pattern features and the gully characteristics are not always observable. Usually 
additional elements are needed to assist with prediction of presence of granular soils. 
Climatic conditions may also temper the erosional features, i.e., even sand and sand clay 
soils in temperate zones have the gully forms of granular terrain. One must use cau- 
tion when making predictions in such regions. 
Photo gray-tones. 
The black, white and gray tones of photo images. form a pattern representing certain 
ground features. The way in which these tones combine themselves in the image gives 
the interpreter a great deal of information which is used to identify a given photo 
pattern as representative of a given soil characteristic. Of course the gray tones of a 
partieular pattern reflect such features as topographic positions, soil texture, soil 
moisture and ground water existing at time of photography, and vegetation. Light color 
tones generally reflect high and dry positions, and the darker tones reflect higher 
moisture conditions. The porousness of the soil can also be observed as a degree of 
grayish blackness of the image. 
One identifying feature of a granular ground condition is observed in form of 
light and dark “tapioca-pudding” type of spottling or mottling shades of gray. These 
mottlings in the photo pattern are generally found to be representative of granular soil 
conditions. 
Vegetation. 
Vegetation may or may not have any significance. Vegetation is of significance 
when the situation is one with the virgin forest, having never been cleared. Civilized 
man has cleared most of the virgin timber except in the far north, in jungles, low 
altitudes, or mountainous inaccessible sites. Another factor is that vegetative ground 
conditions tend to reflect the climatie conditions. For example, dry areas of temperate 
zones are usually grassland, but humid regions of these same zones are covered with 
either forests or croplands. Wherever man allows the forested regions to remain, the 
growth will reflect the soils supporting such vegetation. Agricultural crops such as 
wheat and corn are significant ground cover in some parts of the world. In the arid 
western states of the U.S.A. the drier soil conditions support wheat, and the wetter soil