[dowling] western GAS FIELDS 91 



mutual aid a more ready response was met with. We have on the 

 plains area a great number of shallow wells and a few deep enough to 

 give stability to parts of the area mapped. 



The first approximation to the shape of the beds at present 

 composing the groundwork of the plains indicates that the various 

 layers conform to a very large basin form; that is, a bed which out- 

 crops along the edge of the Cretaceous plateau and is found again 

 in the foothills will be found at various lower levels between these 

 points. In Canada there seems to be two very low points in the basin 

 separated by a slight upraise. Neither of these depressions is open, so 

 that unless since the deposition of the sediments in the sea there had 

 been periods of elevation and local tilting, the porous measures would 

 still contain the original sea water that was not expelled by the load 

 above, and parts of the basin could be considered as saturated and, 

 therefore, of little value for gas production. 



A study of the various wells has shown that this line of saturation 

 exists and is to be found at various levels. The variations may be 

 due to structural causes or the possible addition of water from the 

 surface, or even from gas pressure in the higher parts, but it can be 

 assumed that salt water will be encountered below sea-level. It is 

 necessary then to map the undersurface structure of the various 

 porous beds which may contain gas or oil, but as these beds range 

 from land deposits to offshore sandy silts their continuity cannot be relied 

 upon; so that, as a preliminary, a horizon at the approximate base of 

 the Colorado group has been assumed and structure contours for this 

 plotted in the diagram, Figure 1. From this it is apparent that the 

 areas of the sandy measures from which gas may be expected are 

 reduced by the elimination of all the area below sea-level in so far 

 as the lower sands are concerned, and by the elimination of successively 

 smaller areas of the sands of the Colorado group. The size of the 

 areas of the Colorado group eliminated varies with the elevation as 

 shown in the figure. For example, a sand 500 feet above the approxi- 

 mate base of the Benton formation or above the top of the assumed 

 Dakota horizon may be saturated by salt water and, therefore, of 

 doubtful value in all areas outlined by the contour given on the 

 diagram as 500 feet below sea-level. 



The elimination of large areas as undesirable is thus indicated, so 

 that detailed study and prospective drilling may be directed to the 

 most promising parts at once. 



In reference to the assumed horizon called the top of the Dakota 

 it seems necessary to refer to the difficulty in making, even at the pres- 

 ent time, an accurate correlation of the beds underlying this large 

 area. The Dakota formation is now restricted in the type locality 



