102 THE ROYAL SOCIETY OF CANADA 



the rivers were carried muds and sands, the latter composed almost 

 wholly of the finer chert fragments from the residual mantle of the 

 adjacent Palaeozoic limestones to the west. Vegetation was abundant 

 and luxurious, and at several recurrent intervals thick masses of 

 virtually pure vegetable matter were accumulated which to-day form 

 coal seams. As the lakes shifted, shifting some of this vegetable 

 matter with them, it was covered with cherty sands, which form the 

 characteristic Kootenay sandstones of to-day. During this stage of 

 freshwater sedimentation continual sinking took place, and the region 

 was bent down into a trough whose eastern edge is defined by the 

 eastern feather-edge of the Kootenay formation of the present, which 

 is probably not far east of the western edge of the great plains. The 

 western edge of the trough can not be defined at present; the Kootenay 

 river may be set as its boundary. 



The western exposures of the present day Kootenay strata are 

 notably coarser than those occurring farther east, especially in the 

 upper portion of the formation (22, a), (32,b), so it is apparent that 

 the westward land from which the debris came was rising, and its 

 streams gaining in power (26, b), (37,a). Finally an accelerated up- 

 lift raised the westward land relatively higher, drained the eastward 

 region of its lakes, and closed the Kootenay stage. The rejuvenated 

 streams spread over the newly exposed soft lake sediments, and re- 

 moved a portion of them, covering the remainder with a veneer of 

 cherty and quartzitic pebbles, the last remaining coarser residual chert 

 and quartzitic debris of the land to the west. This gravel was spread 

 evenly over an enormous extent of territory and is now found over- 

 lying the Kootenay formation throughout the southern Rocky moun- 

 tains (8,b), (18,a), (24,a), (27,b), (32,b), (41,a). 



Following this erosion and deposition of conglomerate, renewed 

 subsidence again caused freshwater lake basins to form, but the lakes 

 were smaller, shallower, and less persistent than those of Kootenay 

 time, for the sediments are distinctly more lenticular, less sorted, and 

 contain red beds. For these reasons the massive green sandstones 

 of the Blairmore formation of southwest Alberta are unreliable as 

 horizon markers. These sandstones carry plant remains and fresh- 

 water molluscs in thin limestone bands (24,b), (27,b) and have been 

 given the name Blairmore formation by Leach (19, a), (41, b). 

 The upper Blairmore formation contains claret coloured shales and 

 sandstones and these with their ripple-marks and mudcracks indicate 

 terrestrial sedimentation. 



A thin bed of tufï in the Blairmore (18,b) is the result of slight 

 volcanic action, which culminated in the Crowsnest volcanic episode, 



