3fesozoic and Ccenozoic Geologyand PalcBontology. 173 



western border of the Cretaceous seems, in some places, to follow 

 closely along the base of the Rocky Mountains, but many circum- 

 stances arise to complicate it in that region. 



The Lignitic Group north of the 49th parallel is not bounded by any 

 great physical features of the country, but adheres closely to the upper 

 members of the Cretaceous. Though, no doubt, originally deposited 

 in extensive basin-like depressions, it is now generally found forming 

 slightl}^ elevated plateaus. Denudation must have acted on these 

 rocks on a vast scale, but they still cover an immense area, and con- 

 tain the greatest stores of mineral fuel known to occur in the vicinity 

 of the 49th parallel. The line of their eastern edge crosses the parallel 

 near the 102d meridian, and thence appears to pursue a north-west- 

 ward course, remaining for some distance nearly parallel with the edge 

 of the third plateau. Beyond the elbow of the South Saskatchewan, 

 though the same physical feature continues to the north, it is not 

 known what relation it may bear to the outcrop of this formation, nor 

 has its northern limit been ascertained. 



On leaving the Lake of the Woods, and proceeding westward, the 

 face of the countr}^ is found to be thickly covered with drift and alluv- 

 ial deposits. The Silurian limestones, which probably exist at no very 

 great depth, are not observed, and the first rocks seen are those of the 

 Cretaceous aloAg the base of Pembina mountain, which bounds the 

 Red river valle}^ on the west. From this point westward to the base 

 of the Rocky Mountains no rocks are found older than the Cretaceous. 

 About 25 miles north of the Line, where the Boyne river cuts through 

 the Pembina escarpment the Niobrara Group is found exposed. The 

 rock is a cream-colored or nearly white limestone, breaking easily 

 along horizontal planes, parallel to the surfaces of the shells of Ostrea 

 cojigesta, and InocetYcmus, of which it is in great part composed. The 

 rock also abounds with more or less perfect remains of Foraminifera, 

 Coccoliths, and allied microscopic organisms. Prof. G. M. Dawson 

 here proposes the name of Pembina Mountain Group for what he 

 supposes may be the equivalent of the Fort Pierre Group. It is ex- 

 posed in the vallc}^, by which the Commission Trail ascends Pembina 

 mountain, about ten miles north of the 49th parallel, and where tbe 

 49th parallel cuts the base of the Pembina escarpmtent rocks, and at 

 various other places for about 40 miles west of the foot of Pembina 

 mountain. In some places the exposures vary f]*om 100 to 240 feet. 

 From this point for 350 miles west no exposures of the Cretaceous 

 occur on account of the drift deposits which cover the surface. When 

 the rocks underlying the drift are again seen, near La Roche Percee, 

 they belong to the Lignitic Group. 



