4 
MUSEUM BULLETIN NO. 21. 
of 537 feet above Lake Winnipegosis. One of these old gravel 
bars is exposed at Grand rapids in the Saskatchewan river just 
west of the old cut-off channel. This bar or beach lies about 30 
feet above the river and follows the high ridge northward an 
undetermined distance. South of Pas another of these old 
beaches composed of limestone gravel is seen along the railway. 
It lies upon the morainal ridge of glacial till across which the 
river cuts at Pas. One of these old gravel beaches is crossed 
by the Hudson Bay railway just south of Westray. 
The present drainage system is superposed on the old bed of 
Lake Agassiz. The numberless lakes which represent the last 
stage in the disappearance of the waters of this ancient lake are 
generally connected either permanently or temporarily with the 
Saskatchewan through which their outflow reaches Lake Winni- 
peg. In time of high water, some of these lakes act as temporary 
receivers of the surplus water of the river. The load of silt 
carried by the strong current of the river from its upper reaches, 
finds in these broad, shallow lakes the still- water conditions neces- 
sary for the deposition which will eventually lead to their total 
extinction. In the case of the small lakes of the Saskatchewan 
valley the accumulation of the remains of plants is the most 
important of the agencies which add to their deposits and lead 
to their ultimate filling. A number of plants which thrive best 
in water contribute to this result by adding each season their 
remains to the accumulating mass at the bottom of the lake. 
Some of these, like the rushes which are so universal a feature in 
the muddy shallows of most of the lakes, flourish in water 6 
to 8 feet deep. The most conspicuous and abundant of these is 
the rush Pkragmites communis , growing 12 to 18 feet high and 
thriving best in water 4 to 6 feet deep. This plant always joins 
the advance guard of the water plants and for miles along the 
lower part of the Saskatchewan forms an almost impenetrable 
wall, making approach to the shore often impossible for a con- 
siderable distance. 
The Saskatchewan river has some interesting features in 
the lower part of its course between Pas and Cedar lake. Through- 
out the 100 miles of this part of the course it flows across a flat 
country, its channel cut in the old lake clays of Lake Agassiz. 
