498 PLEISTOCENE OF INDIANA AND MICHIGAN. 



Milk River. — Milk River is a very small stream, but it shows pronounced drowning, as 

 may be seen from the car on the electric line about 4 miles north of Grosse Pointe. 



Southern tributaries. — On the Canadian side eight small creeks enter Lake St. Clair from the 

 south, and all of them show drowning very clearly. No data as to their depths were obtained, 

 but their condition is readily seen along the Grand Trunk Railway, which skirts the south shore. 



Thames River. — The Thames is the largest tributary of Lake St. Clair. Soundings show 

 depths of 18 to 22 feet for several miles from the lake, and it is navigable for small steamers 

 to Chatham, about 16 miles above the mouth. Baptiste and Jeannette creeks, which enter 

 the Thames on the south side near its mouth, are also plainly drowned. 



Sydenham River. — Sydenham River enters the Ecarte Channel of the St. Clair delta about 

 6 miles above its mouth. At Wallaceburg, about 2\ miles above the channel, the two branches 

 of the Sydenham meet and both show well-marked drowning. The south branch i$ navigable 

 up to Dresden, 10 miles above Wallaceburg. 



TRIBUTARIES OF ST. CLAIR RIVER. 



Belle River. — For about 3 miles above its mouth Belle River resembles a deep natural 

 canal. Its value as a harbor for small lake craft determined the location of Marine City at 

 its mouth. Its general depth is 12 feet. 



Pine River. — The lower mile or two of Pine River has a general depth of 12 feet and is 

 an excellent harbor for small lake craft. This fact determined the location of St. Clair. 



Black River. — Black River is considerably larger than the Pine and the Belle and for 

 about 3 miles above its mouth shows depths of 10 and 16 feet. It is a typical example of 

 an overdeepened and drowned stream. 



Canadian tributaries. — On the Canadian side a few very small creeks, such as Talford Creek, 

 a mile above Corunna, and Clay Creek, 3 miles above Sombra, seem to show (on the Lake 

 Survey chart) slight drowning, but their condition has not been actually observed. 



PROGRESS OP OVERDEEPENING AND DROWNING OR FLOODING. 



During two periods, after the retreating ice sheet began to uncover the Great Lakes region, 

 the upper three lakes discharged eastward from Georgian Bay, and Detroit and St. Clair rivers 

 ran dry. During these two periods the relatively small local streams worked to a new and 

 lower base-level and deepened their lower courses considerably. 



FIRST DEEPENING. 



Early Lake Algonquin had a comparatively short life, for the discharge soon left the Port 

 Huron route and went to Kirkfield, Ontario, where it appears to have remained for a relatively 

 long time. (See p. 410.) During this time some deepening at the mouths and in the lower 

 courses of the tributaries may have been accomplished, but it is doubtful whether any recog- 

 nizable evidence of it now remains. At the close of Early Lake Algonquin, St. Clair and Detroit 

 rivers had probably only cut through the St. Clair and Detroit barriers and the softer parts of 

 the Trenton barrier. They had not sunk into the deep beds in which they now flow. 



The upper Algonquin beach and the first St. Clair and first Rouge beaches represent the 

 water levels at that time. The general bottom levels of St. Clair and Detroit rivers were at that 

 time probably not much, if any, below the present water surfaces of these rivers. During the 

 third or Kirkfield stage of Lake Algonquin the beds of St. Clair and Detroit rivers were dry for 

 a relatively long time. The first period of deepening was, therefore, to a higher base-level than 

 the later one, for it was to the abandoned, immature, and only partly developed channel of the 

 outlet of Early Lake Algonquin. 



When the discharge of the upper lakes left Kirkfield it was probably divided in unknown 

 proportions between two outlets, Port Huron and Chicago. The return of large volume to Port 

 Huron drowned the lower courses of the channels which the tributary streams had cut to the 

 dry beds, but the drowning effect was probably slight. 



