Measurements of the thickness of rock sequences and description of their lithology and fauna are much less valuable if the location and elevation of these 'sections' are not known with reasonable accuracy.
Photographs by Nestor John Sander
Therefore, a major part of the work of the geologists in 1950 was to plot the location and to determine the elevation of the the 'sections'. In beds of very low dip the distance from bottom to top of a unit could be measured and the true thickness calculated trigonometrically. They did both tasks using the odometer of the sedan to measure distance in kilometers and surveying altimeters to determine the elevation of a given point in feet. Today, both can be measured via satellite with greater accuracy and much more rapidly.
The elevation and location of the starting point of a traverse are known. The Brunton is set up to determine the azimuth of the first point for the car to drive toward. On the way there, at recognizable and well-marked sites, the bearings or prominent landmarks, locations known or to be determined, are tied into the traverse line. The succeeding legs of the traverse follow the same procedure with the aiming point of the next leg chosen at the end of each. Geologic and topographic data are recorded as the traverse continues. the last leg returns to the starting point or ends at another point with known coordinates. The angles, elevations and distances recorded must bring the calculated end of the final leg as nearly as possible to the origin of the traverse or to the know point where it terminates.
For the odometer to be a reasonably accurate measuring devise, it was calibrated over a measured two kilometers with the tires held thereafter at the same pressure. Heat made regulation of pressure an oft-repeated chore. Calibration was done again when tires where changed. Broken speedometer cables brought surveying to a halt until replaced.
The altimeter marked changes in altitude to a foot, but constant fluctuations in barometric pressure made the use of two altimeters imperative, one remaining at the base or in a long traverse at the previous station until the new station had been reached. Thus a change in reading in both instruments could be used to correct the second reading. This is called 'a double barometer traverse'.