J. B. Tyrrell — Cretaceous of Manitoba. 229 



considerable quantity of carbonaceous material. This shale is 

 evenly bedded and breaks down readily into thin flakes, on 

 which account it generally forms sloping banks. With the 

 dark shales are associated thin beds of white soft sweet-tasting 

 magnesian clay. In the borehole on Vermilion River the Ben- 

 ton appears to be 130 feet thick, and farther north, on the 

 face of the Duck and Porcupine Mountains, it continues of 

 about the same thickness. It is easily recognized, even when 

 good naked exposures are absent, by its characteristic property 

 of breaking into more or less minute graphite-like flakes, and 

 not weathering immediately into a soft clay as usually occurs 

 in the less consolidated beds of the Pierre. 



In the Deloraine well this terrane has been recognized in 

 specimens from a depth of about 1300 feet. Up to the present 

 it appears to be quite destitute of fossils, and ironstone or lime- 

 stone nodules were also only found in one or two localities. 



The Niobrara Group conformably overlies and is an upward 

 extension of the Benton. The character of the rock, however, 

 instead of being a soft fissile shale with little or no admixture 

 of calcareous material, is a lighter gray calcareous shale or marl, 

 sometimes varying to a band of moderately hard limestone. 

 This is especially the case at the top of the formation where a 

 band of grayish chalky limestone is generally met with. This 

 band is often highly charged with pyrite. 



The rock throughout is strongly marked by the presence of 

 a large number of Foraminifera belonging to such genera as 

 Globigerina, Textularia, etc., and of the larger fossils a gigantic 

 Inoceramus is very common, while Ostrea congesta, Belemni- 

 tella Manitobensis, Ptychodus parvulus, JEnchodus Shumardi, 

 and Cladocyclus occidentalis have also been recognized. 



The outcrop of this terrane has already been recorded in 

 Manitoba by Dr. Dawson from the Boyne River, twenty-five 

 miles north of the 49th parallel of latitude. Dr. Selwyn has 

 recognized its occurrence on the Assiniboine River thirty miles 

 above Portage la Prairie, and Dr. Spencer also discovered it in 

 the valley of Swan River. South of the 51st parallel of lati- 

 tude, the Riding Mountain has not been examined, but from 

 the Ochre River northward, along the face of the Riding, Duck 

 and Porcupine Mountains, this formation is easily recognized 

 in the valleys of many of the streams that cut deep gorges 

 through the drift. It often weathers out in steep or vertical 

 cliffs and may easily be recognized as a gray calcareous shale 

 having a more or less mottled appearance from the presence of 

 large numbers of Foraminifera, and occasionally included bands 

 of chalky limestone. 



Throughout the greater portion of the area it does not 



Am. Jour. Sci.— Third Series, Vol. XL, No. 237.— Sept., 1890. 

 15 



