PREGLACIAL CONDITIONS AND LIFE 201 



times. 15 Near Des Moines a number of preglacial "cut-outs" have been located 

 while sinking mine shafts. Other buried channels have been found in different 

 parts of the glaciated territory, but they need not be referred to at this time. 

 In southeastern Wisconsin, Alden 15a has traced a number of preglacial channels 

 buried beneath glacial till, several of these draining into Lake Michigan. 



A few years ago, 18 Prof. A. W. Grabau, using the data published by Spencer 

 and other geologists, worked out a theory of preglacial drainage, in which 

 the main or consequent streams are made to flow south westward, or in a trans- 

 verse direction to the Niagara cuesta. Four streams are postulated; (1) a 

 stream flowing thru the narrow straits of Mackinac into the Lake Michigan 

 basin; (2) a large stream, the Saginaw River, flowing southwestward thru 

 Georgian Bay and Lake Huron; (3) a large river, the Duhdas, flowing from the 

 highlands of Canada thru the western end of the Ontario basin, thence by the 

 buried Dundas Valley to the Erie basin; and (4) the ancient Genesee River, 

 flowing across the Ontario basin into southern New York. These four major 

 streams are shown by later adjustment (principally piracy) to develop into 

 two large river systems, the Saginaw and the Dundas (Plate LV). The valleys 

 of Cayuga and Seneca lakes are made to contain southward flowing streams 

 and the beheaded Genesee flows southward. This theory of Tertiary drainage, 

 while highly ingenious, does not seem to accord with the known data, when 

 surveyed as a whole, as well as does that of Spencer. The indicated direction 

 of the Genesee River is not in accord with the facts as presented by an examina- 

 tion of the territory, nor does Prof. Grabau give sufficient weight to the old 

 valley of Irondequoit Bay which has been shown by Fairchild to be the ancient 

 outlet of the Genesee. The buried channel between the Erie and Ontario 

 basins, which is given such weight by Spencer, is not given sufficient promi- 

 nence in this theory. 



Miller 1 6a considers Grabau' s interpretation more tenable than Spencer's 

 theory of a preglacial St. Lawrence drainage. The St. Lawrence is said to be 

 almost certainly postglacial in its course at the Thousand Islands as shown 

 by the lack of any real channel, and by the presence of a belt of hard pre- 

 Cambrian rock extending across the river and connecting the Adirondacks 

 with the Canadian pre-Cambrian rocks. This hard rock belt is thot to have 

 formed a preglacial divide until the recent formation of Lake Ontario and the 

 downwarping of the land, which allowed the drainage to pass over the divide 

 for the first time (p. 82). The drainage of the St. Lawrence is believed to have 



B See Iowa Geol. Sun-., Ill, pp. 239-255, 1895; also Leverett's 111. Glacial Lobe, pp. 

 468^69; Keyes, Iowa Geol. Surv., II, pp. 183-185, 292, 346, 1894. 

 154 Professional Papers, U. S. Geol. Surv., 106, pp. 102-128, 1918. 

 16 Geol. and Pal. of Niagara Falls and Vicinity, pp. 37-54. 

 163 Bull. N. Y. State Museum, No. 168, pp. 82-86; 96-107, 1913. 



