394 THE GLACIAL LAKE AGASSIZ. 



the crest of which is \,\d5 feet above tlie sea, with a descent of about 5 

 feet on the west and 10 feet on the east. A half niik^ farther east it cuts 

 the Liwer Norcross beach, with its crest at 1,167 feet, from which there is a 

 descent of 10 feet to the west and 15 feet to the east. This beach has been 

 extensively excavated for ballast, a spur track being- run along its course a 

 quarter of a mile northwestward from the railway. The excavation, vary- 

 ing along this distance from 6 to 8 rods in width and from 5 to 15 feet in 

 depth, shows that the ridge is composed of interbedded sand and gravel, 

 the layers of sand constituting about half of the entire deposit. The 

 gravel layers differ in coarseness from those that contain no pebbles more 

 than 1 or 2 inches in diameter to others containing waterworn masses of 

 shale a foot across and Archean cobbles 6 inches in diameter. By esti- 

 mate, nearly nine-tenths of the gravel is the hard Fort Pierre shale which 

 makes up the principal mass of the Pembina Mountain, the Tiger Hills, 

 and Riding Mountain, this shale gravel being often almost unmixed with 

 other material ; alwut a twentieth part consists of two classes of limestones, 

 derived in nearlj- equal proportions from the yellowish-gray arenaceous 

 limestone of Niobrara age, plentift;lly fossiliferous, which outcrops beneath 

 this shale on the Boyne and Assiniboine rivers, and from the Paleozoic 

 limestones of the flat country about Lakes Manitoba and AVinnipeg; and 

 the remaining twentieth is from the Archean rocks that lie east and noi'th 

 of Lake Winnipeg. Continuing northwesterly and northerly, this massive 

 beach ridge crosses sections 8 and 17 and the eastern edge of section 19, 

 township 8, range 9, beyond which it is lost sight of on the undulating and 

 pai'tly wind-blown surface of the Assiniboine delta. 



The next definite observations of the Norcross shores of tliis lake are 

 near Neepawa, where the Manitoba and Northwestern Railway, a half mile 

 west of this station, crosses small beach ridges referable to the upi^er Nor- 

 cross stage, with their crests 1,223 to 1,225 feet above the sea. Close to 

 the west is an eroded escarpment of till 15 feet high, rising from 1,225 

 to 1,240 feet. On tlie other side of the station, between a half mile and 

 1 mile east from it, the railway crosses a surface of wind-blown sand with 

 hollows 2 to 4 feet deep, the crests of its low dunes being at 1,193 to 1,192 

 feet. These occupy the level belonging to the lower Norcross beach. The 



