480 PLEISTOCENE OF INDIANA AND MICHIGAN. 



line its -width is about 20 miles and it is estimated to have filled about one-quarter of Lake St. 

 Clair. The delta is made up of islands separated by somewhat winding distributary channels. 

 It has not all been made with the lake at its present level, for the ground toward its head stands 

 about 6 feet above the mean level of the river. The surface of the delta is extremely flat and 

 slopes very evenly, its front being a submerged flat 2 to 3 miles wide. Its outer edge is fairly 

 well defined at a depth of 6 or S feet by a rather definite bank from which the descent is rela- 

 tively abrupt to the deeper part of the lake. The greatest depth of the lake is 22 feet, with a 

 general depth in the central part of about 20 feet. Thus, the delta surface slopes 12 feet from 

 head to front but slopes a little more rapidly near the submerged edge. 



The steepness of the sides of the channels under water is most remarkable, being sometimes almost vertical for a 

 distance, while a greater dip than 45° is probably characteristic. There are nine channels, including Baltimore 

 channel and the ship canal, which have a depth of over 3 fathoms to the bars at their mouths. Throughout the 

 most of then- length the main channels have an average depth of about 30 to 40 feet, but the north channel, in the 

 large bend south of Algonac, reaches a depth of 90 feet and is 60 feet and more deep to some distance below the North 

 Channel clubhouse at the junction of the Chenal a Bout Rond. The river above the head of the south channel ranges 

 in depth from 30 to 60 feet. 1 



Toward the head of the delta large areas on Russell, Herson, Squirrel, and Walpole islands 

 are well above mean water level, are partly covered with heavy forests, and partly under cul- 

 tivation. The height of these islands above mean water level shows that they were built when 

 Lake St. Clair stood higher than now. The fall in the lake level has caused the river to deepen 

 its channels through the older parts of the delta. 



A glance at the excellent chart of Lake St. Clair by the United States Lake Survey (edition 

 of August, 1908, or later), which is indispensable for studying the outline of the delta and the 

 width and depth of its various channels, shows that the delta as a whole is divisible into two 

 main parts, the old and the new. The dividing fine is along the east side of the South Channel. 

 Squirrel, Walpole, and Ste. Anne islands and probably the marshy flats west of the Bassett 

 Channel belong to the old part. Russell, Hereon, and Dickenson islands, though their higher 

 or northern parts are probably as old as Walpole Island, are associated with the new channels 

 and the newly made part of the delta. There are, however, some evidences that Hereon 

 Island is partly of relatively recent date, for irregular shallow sloughs run through its northern 

 hah in several directions. The islands east of the South Channel show no such features 

 containing water. 



The moving current of the river carries the fine sediments in suspension when the water is 

 roily and rolls the sand along the bottoms of the larger channels. The growth of the delta 

 takes place chiefly in the shallow waters along the sides and around the ends of the channels, 

 where these are active and reach nearly to the delta front. Big and Little Muscamoot, Goose, 

 and Fisher bays are being gradually filled up in this way. Even where the channels are deep 

 to within a mile of the submerged edge of the delta, they end abruptly in the shallows behind 

 a wide flat bar. As the platform of the delta is built out the deep channels follow, but never open 

 directly into the deeper part of the lake. 



CHANNELS OF THE NEW DELTA. 



The channels now active are the South, which is the principal fine of navigation, and the 

 North, wliich has two branches from its south side, the first of which is called the Middle 

 Channel and the other, farther west, the Chenal a Bout Rond, or locally the Sny. The main 

 line of the North Channel, which runs westward from Algonac, is the largest in cross section, 

 has the swiftest current, and carries the largest volume of water. The upper part of these 

 channels, for 3 to 4 miles below Algonac, are simply deepened passages through the older part 

 of the delta and vary from an eighth of a mile to half a mile in width. The land there is 

 slightly above high water and can hardly be said to be growing. Farther out, however, the 

 channels pass beyond the dry-land surface and run for 4 or 5 miles out into the shallows of 



i Cole, L. J., Michigan Geol. Survey, vol. 9, pt. 1, 1903, pp. 6-7. 



