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Chapter 3: Geologic Structure and Landforms

3.4: Structural Features on the Precambrian Shield Southwest of Shamattawa

The photograph shows part of the poorly drained Precambrian Shield in northeastern Manitoba. In this area the bedrock is mapped as “felsic granulites and associated granitoid complexes with minor gabbro and anorthosite”[i] but organic surficial materials cover most of it. North Opuskiamishes Lake 1 at 137+ metres above sea level[ii] drains via North Opuskiamishes River 2 to Gods River (off the photograph). The course of the former river is structurally determined with a right-angled bend at 3. Other obvious structural lines can be seen at 4, 5, 6 and 7 with less clear examples at 8 and 9 and a complex of joints at 10. The pattern at 11 surrounding a small lake results from strings of vegetation separated by pools of water. The variable tones of the lakes on this photo result from variations in the lake surface/sun angle/camera lens relationship. However, the light tone at 12 in North Opuskiamishes Lake is caused by sediment washed in by a river.

This is the first photograph in a series (contract 711) and the specifications for the job are given in the top left-hand corner 13. The photographs were obtained from a height of 30,000 feet above sea level using a camera with a focal length of 6 inches with a Wratten no. 12 filter. Flight lines were from north to south (photo numbers 1 to 36), south to north (photo numbers 37 to 66), etc. Using the information provided it is possible to calculate the scale of the photograph using the equation f/h=i/o where f=focal length of the camera; h=height of the camera above ground level; i=image distance, that is, the distance between two objects on the photograph; and o=object distance, the distance between the same two objects on the ground. In effect i/o is the scale of the photograph. When doing the calculation, f and h must be expressed in the same units. So in this case

f=6 inches or 0.5 feet

h=30,000-449 (the height above sea level of North Opuskiamishes Lake on the 1:250,000 topographic map, 53 N Gods River).

So the scale is 0.5/29,551 or 1/59,102

The scale is 1:59,000 approximately—allowing for height variations within the area covered by the photograph.

Figure 3.4: Structural Features on the Precambrian Shield Southwest of Shamattawa

Figure 3.4: Structural Features on the Precambrian Shield Southwest of Shamattawa

Figure 3.4

Vertical air photograph: A14215-1

Flight height: 30,000 feet a.s.l.; lens focal length 6 inches

Date: July 7, 1954

Scale: 1:39,000 (approx.)

Location: Township 76, Ranges 9 and 10 EI

Map sheet: 1:250,000 53N Gods River

1:50,000 53N/10 East Niska Lake


[i] Geological Survey of Canada. Geological Highway Map of Manitoba 1994. Winnipeg: Geological Survey of Canada, Manitoba Minerals Division, 1994.

[ii] From NTS 1:250,000 map, 53N Gods River, 1987.