322 
W. TF. Olive: Tonal 
Lineaments on the 
Aerial Photograph. 
quelques levers de faible étendue ont été réalisés en diverses régions de France. 
La cadence à laquelle sont établies les cartes photogéologiques est de l’ordre de 
20 000 km 2 par mois. Le prix de revient du kilomètre carré varie en fonction de 
l’échelle des cartes demandées et des difficultés locales d’observation et d’inter 
prétation. Il est en moyenne de 500 Frs. pour les cartes au 50 000 e . 
An example of Exploitation of Aerial Photography on an Industrial 
Scale in France 
The rapidly increasing development of mining and petroleum prospecting in the African territories 
of the French Union has led the prospecting companies for some years to use systematic aerial 
photography to establish topographic and geologic maps necessary to their research. Morphologic 
and structural maps may be made from aerial photographs, particularly in regions where no 
topographic maps exist. These maps help in preparing and orientating future research, and 
accelerate and facilitate the work of the field geologists. 
The importance of photogeology has led the Institut Français du Pétrole to create a specialized 
department able to fill the ever increasing needs of the mining and petroleum industries. This 
department does interpretation of aerial photographs on an industrial scale. It was recognized early 
that to reach its maximum efficiency, photogeologic studies should be done on a large scale by 
specialized teams of photogeologists, photogrammeters and cartographers. A trained geologist may 
be able to interpret a few aerial photographs covering a small area by himself, but to interpret a 
large region, the collaboration of photogrammeters and cartographers will be needed to compensate 
for the distortion and the changes of scale before establishing the final map. 
At the present time, the photogeologic department of the Institut Français du Pétrole is divided 
in three sections: 
1°— the bureau of photogeological interpretation where twelve photogeologists analyse and interpret 
aerial photographs. 
2°— the bureau of photogrammetry, where four photogrammeters, three assistant photogrammeters 
and two photographers do triangulation, adjustment and bring the data to scale. 
3°— the bureau of cartography where thirty draftsmen-cartographers are responsible for drawing 
and printing the maps. 
By virtue of this organization, the department of photogeology of the IFP has been able to 
assume the photogeologic interpretation of about 500 000 square kilometers for several petroleum 
companies and Bureau of Alines. Alost of the areas studied are in North Africa and the Sahara. 
A study was done in French Guinea for the »Direction des Alines de l’A. O. F.», and several small 
areas have been surveyed in different regions of France. A coverage of 20 000 square kilometers of 
photogeologic maps is done every month. The cost per square kilometer is a function of the map 
scale, and of the difficulties of flying and interpretation. It is about 500 Frs for maps with a scale 
of 1/50 000. 
Dr. John Roscoe of U.S.A., presented a paper by Mr. W. W. Olive of U.S.A., 
on Tonal Lineaments on the Aerial Photograph: 
Tonal lineaments are narrow bands of light or dark tone that are visible on 
aerial photographs. Many lineaments are seen at a cursory glance; however, others 
are relatively inconspicuous and can best be seen by viewing aerial vertical 
photographs (individual prints or mosaics) at an angle near parallel with the 
surface of the photograph, with the line of sight directed toward a non-reflecting 
background and the surface of the photograph illuminated by a source of light 
placed behind the observer. The magnitude of tonal lineaments seen on photo 
graphs is dependent largely on the scale of the photograph. Local lineaments 
can best be seen on large scale (about 1: 20 000) photographs, and sub-regional 
to regional lineaments can best be seen on small scale (about 1: 200 000) mosaics 
or photographs. Lineaments of even greater extent are visible on high altitude 
photographs such as those taken from rockets 100 miles above the earth. Tonal 
lineaments visible on Mars (as »canals») and the moon are continuous for 
several hundred and even thousands of miles. 
Most tonal lineaments probably have a structural origin. In the Gulf Coastal 
Plain of the southern United States, tonal lineaments that continue for tens of 
miles mark the positions of Recent and Pleistocene faults and fault zones. In 
West Texas tonal lineaments have been observed to mark positions of faults,