b) Drainage and erosion:
The density and pattern of drainage channels in a given area directly reflect the nature of the underlying soil and rock.
THIS ANALYSIS IS VERY IMPORTANT. YOU MUST FOLLOW THE FOLLOWING PROCEDURE.
The drainage pattern must be accurately traced on an overlay sheet to allow the pattern to be successfully studied and interpreted. It may be possible to interpret lithology fairly accurately through a study of the drainage pattern.
Drainage patterns and generalized interpretations-
A closely spaced pattern denotes relatively impervious bedrock; widely spaced drainage suggests pervious underlying materials; a tree-like pattern develops in flat lying beds and relatively uniform bedrock; a parallel pattern indicates the presence of a regional slope; a radial pattern indicates a domal structure; a haphazard pattern is found in glaciated areas or in areas subjected to large scale landslides; a feather like pattern is common in areas of severe erosion in rather uniform silty materials. Drainage is often controlled by the structure. Fault-controlled valleys are common in Jamaica.
The shape of gullies appearing on photos may provide clues to surface or near-surface materials: long, smoothly rounded gullies indicate clays; U-shaped gullies, silts; short V-shaped gullies, sands and gravels.
For details on drainage patterns consult standard geomorphology textbooks.

c) Soil tones represent a record of the radiation that has been reflected from the Earth's surface onto the photographic film. On black and white photographs, the tones are merely shades of gray, ranging from black to white. Soil tones are easily recognizable unless there is a heavy vegetation cover. Gray tones are highly respondent to soil moisture conditions on the ground and are, therefore, very important in landslide investigations.

A soil normally registers a dark tone if it has a high moisture content and a light tone if has a low moisture content. Peat soils may appear with dark gray tones; calcareous soils are with a light gray tone.