494 PLEISTOCENE OF INDIANA AND MICHIGAN. 



DROWNED IHSTUIHUTARY CHANNELS. 



Besides the distributaries described above, a number of elongated depressions on the 

 floor of the estuary of the Detroit River, evidently the remains of former distributary channels 

 now submerged, are very distinctly marked in several places and are traceable to a depth of 

 15 to 17 feet below the present surface of Lake Erie. 



Southward from the vicinity of Humbug Island two narrow troughs lie in the river floor. 

 One on the east side passes between Calf and Snake islands and Grosse Isle. The other one 

 runs south from Humbug Island and turns gradually southeastward to the deeper water 2 or 

 3 miles from Horse Island. Another channel not so well defined runs south from the west side 

 of Calf Island and with some breaks seems traceable almost as far as the other and is closely 

 parallel with it. Both of these lead southward out of the present Trenton Channel. 



On the east side of Grosse Isle there are several well-marked submerged channels. A very 

 distinct one passes between Sugar and Hickory islands and is traceable for 2 or 3 miles to the 

 south. Another passes just east of Sugar Island and within a half mile appears to branch 

 into two parts which run southwest and southeast around the two sides of an extensive area 

 of bedrock. Another larger channel lies west of Bois Blanc Island, where it divides in two, 

 one branch going south and the other southwest to the channel east of Sugar Island. The 

 main channel also divides north of Bois Blanc Island, one branch passing southwest to the 

 channels just described and the other, which is the present main route of navigation, running 

 south between Bois Blanc Island and the mainland at Amherstburg. A considerable part of 

 these channels north of a line passing through the south ends of Hickory and Bois Blanc islands 

 is more than 18 feet deep; on the west side between Humbug and Celeron islands a number of 

 spots are deeper than 18 feet. All of these and many other details are well shown on recent 

 issues of the United States Lake Survey chart of Detroit River. 



The distributaries in the Trenton-Amherstburg district, including those submerged on the 

 floor of the estuary, have been in process of making whenever Detroit River was flowing in full 

 or nearly full volume. Twice, when this great volume was withdrawn, work on the distribu- 

 taries must have ceased. The channels now submerged were made mainly before the recent 

 rise of the waters of Lake Erie on its western shores, and the making of the estuary is intimately 

 related to this earlier work of the river. The making of the distributaries has been accom- 

 plished in three high stages of the river. The first high stage was during the time of Early 

 Lake Algonquin; during this stage all of the older, higher distributaries, including those east 

 of Rockwood, were made and probably abandoned. The second high stage was during the 

 Port Huron-Chicago stage of Lake Algonquin. The Algonquin uplifts occurred chiefly during 

 this stage. The fact that so many clearly defined distributary channels pass 20 feet or more 

 below present lake level and are submerged this much seems to show that the surface of Lake 

 Erie was slightly lower than now during one or both of the earlier high stages, the present being 

 the third high stage. The amount of difference is uncertain. It may have amounted to 20 or 

 30 feet at first, but toward the close of the Algonquin uplifts in the Port Huron-Chicago stage 

 the water was brought very nearly up to its present level in the west end of the lake. 



RECENT AND PR< )( Mi KSNIN' I CHAMiKM IN DKTROIT RIVER. 



Between Stony Island and Amherstburg and in the west channel between Trenton and 

 Grosse Isle the bottom of the river is nearly everywhere stony. Two considerable areas of 

 rock, one south and the other southeast of Stony Island, are covered by not more than 4 or 5 

 feet of water, and at some points by less. The trend of the main deep channel from its wider 

 part north of Stony Island strongly suggests very recent change, and this is corroborated by 

 the character and relations of the narrow deep channel between Bois Blanc and Amherstburg. 

 The main channel from the north runs a little east of south to the Limekiln crossing, where it 

 enters a majestic curve which bends around to the southwest and passes by the north end of 

 Bois Blanc Island. West of the island it turns south, apparently in two branching courses. 

 This channel appears to have been developed by a slow shifting eastward by erosion of the 



