Holzinger: MOSS FLORA OF THE MINNESOTA RIVER. Ill 



The next week (till July 8) was spent in further exploration 

 below Ortonville. On the return trip stops were made at Mon- 

 tevideo (July 8-10), and at Granite Falls (July 10-15), with 

 such good results as the systematic list of species shows. 



The region of the upper Minnesota river thus explored is a 

 part of the area treated by Professor C. W. Hall in the Bulletin 

 of the United States Geological Survey, No. 157 (1899). The 

 prairies back of the general valley are made up entirely of 

 morainic and drift materials. The valley is from two to four 

 miles and more wide ; and the bordering bluffs are from 150 to 

 200 feet high. Scattered over this valley, in numerous clusters, 

 are the ice-rounded, or frequently jagged outcrops of gneisses 

 and granites mentioned above. In and out among these the 

 present river winds. Not so in the recently past geological 

 time, the time of great Lake Agassiz, now shrunken to a mere 

 shadow of its former self, into Lake Winnipeg and the cluster 

 of lakes surrounding it. At that time, the Red river of the 

 North, instead of flowing into Lake Winnipeg and contributing 

 its waters to the Hudson Bay system, was an outlet from Lake 

 Agassiz in the opposite direction, through the present Minne- 

 sota valley, into the Mississippi system. That ancient river, in 

 the height of its use as a drainage channel for these northern 

 waters, must have appeared more like a great estuary, stretching 

 across what is now southern Minnesota, than like an inland river. 

 And, judging from the stately sweep of its valley, it must, in its 

 time, have received the present Mississippi as a secondary 

 stream of comparatively small volume. That this stream has 

 had a great influence upon the distribution of organisms, notably 

 of plants, along its course, especially during interglacial and 

 postglacial time, as the ice cap receded, can hardly be doubted. 

 I take it that the occurrence in this great valley, to which of 

 course we must add the Mississippi valley proper, of such 

 Rocky Mountain species as the two North American Coscino- 

 dons, of Grimmia brandegei, of Ceratodon conicus, and others, 

 was made possible through that ancient channel. Like stranded 

 strangers, these plants persist among the archaean and silurian 

 rocks of these great rivers, far sundered from their kindred by 

 a climatic barrier at present impassable for them. For, the 

 western border of our state, including the region explored, ap- 

 proaches that doubtful strip across the great North American 

 farm lands between the 95th and looth meridians approximately, 



