Editing Lake Agassiz (section)

== Glacial lakes draining into Lake Agassiz ==
Glacial [[Lake Souris]] formed along the [[Manitoba]] and [[North Dakota]] border, forming a crescent around the west side of the [[Turtle Mountain Provincial Park|Turtle Mountains]]. Lake Souris had three successive outlets: the [[Sheyenne River]], the Pembina River, and finally the Assiniboine River.<ref>(Upham, 1895), pp. 267; 270–272.</ref><ref>The land around former Lake Souris inclines downhill along a northeast direction; thus, as the ice sheet retreated northwards, it exposed outlets of successively lower elevation. (Upham, 1895), pp. 270–272.</ref>  Initially, Lake Souris' southern bay drained into the Sheyenne River, a tributary of the Red River, which in turn flowed into Lake Agassiz.<ref>(Upham, 1895), p. 268.</ref>  However, after the ice sheet had retreated enough to uncover Turtle Mountain, the northern bay of Lake Souris found an outlet at the "elbow" of the modern [[Souris River]]; the elbow is about {{convert|18|mi|km}} southwest of the present mouth of the Souris River.<ref name=UphamII/>{{rp|57}} From this elbow, the lake's waters flowed southeast and entered the [[Pembina River (Manitoba – North Dakota)|Pembina River]], now a tributary of the [[Red River of the North|Red River]],<ref name=UphamII/>{{rp|57–58,268}} and the Pembina, in turn, entered Lake Agassiz at its [[Assiniboine River|Assiniboine]] embayment.<ref>(Upham, 1895), Plate IX (following p. 36).</ref> When the ice sheet retreated north of the Assiniboine River, Lake Souris drained via that river into Lake Agassiz.<ref>(Upham, 1895), pp. 271–272; see also Plate XXI (following p. 268).</ref>  ([[Pelican Lake (Manitoba)|Pelican Lake]] in Langs Valley of Manitoba occupies what was once the northern shore of Lake Souris.<ref>(Upham, 1895), see Plate XXI (following p. 268).</ref>)

The lower part of the [[Saskatchewan River]] basin near the river's mouth at Cedar Lake was clear of the ice-sheet before Lake Agassiz began to drain to northeast.<ref name=UphamII/>  Lake Saskatchewan existed on about {{convert|135|mi|km}} of the [[North Saskatchewan River]] between [[Saskatoon]] and [[Prince Albert, Saskatchewan|Prince Albert]], Saskatchewan. A few miles east of Lake Saskatchewan's outlet, near the modern junction of the north and south branches, it entered Lake Agassiz. This Saskatchewan embayment extended for {{convert|400|mi|km}} along the modern Saskatchewan River route.<ref name=UphamII/>