BENTON FORMATION 



679 



come greenish and light colored. Cairnes succeeded in finding a few plant 

 remains, but in general the formation is remarkably barren of fossils. 



Benton Formation 



The change from the Kootenay-Blairmore continental conditions to the 

 marine Benton is sharply marked all through the foothills. Everywhere 

 the contrast between the greenish shaly sandstones of the Blairmore and 

 the black, thinly laminated bituminous shales of the Benton is noticeable. 

 The same is true of the upper line between the Benton and the Belly 

 Eiver formation. The folding of the massive sandstones of the Blair- 

 more and Belly River formations is intensified to an extraordinary degree 

 in the weak shales of the included Benton, causing a very complex mass 

 of distorted strata whose thickness is extremely difficult of measurement. 

 From many traverses on all the streams of the region, together with the 

 logs of oil wells, it has been possible to compute the thickness of these 

 shales as 2,400 feet. The formation is remarkably uniform in character, 

 varied here and there by thin calcareous bands never exceeding one foot 

 in thickness, and by oval-shaped ironstone nodules of small diameter. 

 There is a thin sandstone and conglomerate horizon in the northern part 

 of the district, which there attains a thickness of nearly 10 feet and has 

 been named the "Cardium" sandstone by early writers on account of the 

 presence of Cardium pauperculum in considerable numbers. The Car- 

 dium horizon, however, is only of local extent near the Bow River and 

 on the Elbow River. Cairnes had used this as a line of separation of the 

 shale group into two formations, the portion above the Cardium horizon 

 being called Claggett and that below being named Benton. The explora- 

 tion of the Benton shales, however, by the author of this paper has re- 

 peatedly resulted in the finding of typical Benton forms at the very top 

 of the shale group or at the top of Cairnes' Claggett, underlying the sand- 

 stone strata of the Belly River formation. The Geological Survey of 

 Canada has of recent years doubted the presence of the Claggett anywhere 

 in the foothills, and the data of this paper bears out this conclusion. 



Of all the Cretaceous formations in the area described in this paper 

 the Benton formation is the most certain. It is unquestionably the equiv- 

 alent of the Colorado shale of the United States. 



Collections of the fauna were made from the various localities shown 

 in the appended statement. Thanks to Mr. H. R. Johnson, of Los An- 

 geles, California, and to Dr. J. P. Smith, of Leland Stanford University, 

 it is possible to publish this list. The following species have been identi- 

 fied as Benton by Dr. Smith : 



XLIX — Bull. Geol. Soc. Am., Vol. 27, 1915 



