92 THE ROYAL SOCIETY OF CANADA 



to a subaerial formation containing a certain flora. As it is difficult 

 to conceive of land conditions as being continuous across a plain 

 which had been at least in part submerged during the Jurassic period, 

 we are obliged to try to trace the marine silts which the Cretaceous 

 sea deposited above these sands. Probably this sea was shallow and 

 parts of it persisted through the time represented by the Dakota; 

 it is quite certain, therefore, that there will be, especially in the areas 

 at a distance from the known land deposit, sands of both earlier and 

 later age. Those sands found along the western margin below the 

 Benton shale are known to have been deposited in successive layers 

 from the close of the Jurassic to the Dakota. On the north, the 

 exact age of the lowest Cretaceous bed is not definitely compared as 

 yet with any American deposit, but may be of Lower Cretaceous age, 

 and as the direction of the transport of the material was from the 

 north the sand beds may not be traced throughout the basin. There 

 seems, however, to be a sand bed or beds beneath the dark marine 

 shales and even in these shales there appear to be some sandy layers. 

 This sandy infiltration is apparently traceable to the western side of 

 the sea where the mountain building was in progress, and is absent 

 in the eastern part. In these sands the best gas accumulations seem 

 to be in beds included in the Benton shales, that is, above the assumed 

 Dakota horizon. Below this there have been traces of oil in some of 

 the lower sands. Whether this is from one horizon or not is not 

 clear, but apparently along the western edge of the basin this oily 

 horizon is Lower Cretaceous, as is also probably that of the Athabaska 

 and Peace River valleys. In the plains area the impregnations seem 

 to be of a very heavy oil. 



In considering the question of oil fields, therefore, the areas 

 probably saturated with salt water are those outlined as having the 

 Dakota horizon beneath sea-level, thus eliminating a very large part 

 of the plains. 



For gas, however, there are larger areas, since the gas is found 

 above the Dakota horizon, but the absence of the Benton sands in 

 the eastern area which apparently includes a large part of Saskatche- 

 wan again reduces the probable parts. Small amounts of gas have been 

 found in the sands above the Benton, so that gas fields of limited extent 

 or flow are possible often where the lower beds cannot be reached. 

 Small flows of gas such as supplied from wells at Castor and Tofield 

 are obtained in the sandy beds of the Belly River formation around 

 the eastern edge of the Alberta syncline. Another instance is the 

 Medicine Hat supply which comes mainly from sands at the top of the 

 Benton. 



