WORKING GROUP 9 
MOLLARD 
521 
Fig. 6. Stereopair showing an extensive pitted outwash plain. Mapped in connection with 
the search for a large railway ballast deposit. Several million cubic yards of sand and gravel 
are indicated in this stereopair. Note the well-defined shape of the kettleholes. 
capacities and so produce poor crop yields in semi-arid or arid climates. 
9. Natural vegetation. Vegetative pattern and vegetative types must be inter 
preted from the standpoint of texture of near-surface materials as well as 
from a consideration of climate and local surface-drainage conditions. 
The airphoto observer gets to know the appearance, variations in appearance, 
and relative significance of each of these photo-identifying features in the 
regions where he has carried out many airphoto studies. 
On the Canadian prairies most granular deposits are proportionately high in 
sand sizes. On the other hand, deep coarse gravelly deposits are very scarce 
indeed. In this region, accordingly, one must try to discover these airphoto- 
identifying features peculiar to coarse glaciofluvial and alluvial deposits. Among 
these are well-defined current markings; anomalously steep sides on kettle- 
holes where these features are present; sharp, angular V-shaped gullies; 
abrupt changes in slope around the crests of kettleholes and at places where 
shallow to deep former channels were cut into a granular deposit. 
Variability in the stratigraphy of a granular deposit can often be inferred 
from mode of sediment deposition in conjunction with environment of deposi 
tion. Where granular deposits lie in valleys excavated into clay shales below