POSTGLACIAL DEVELOPMENT OF CONNECTING EIVEKS OF GREAT LAKES. 493 



back to any great extent by the lake at its present level. This applies to the west shore of 

 the lake from the mouth of Detroit River to Toledo and to the Canadian shore for at least 4 

 or 5 miles east from Bar Point. But from Amherstburg south to Bar Point the land has been 

 cut away in recent times. Whether this cutting has been done by lake waves or by river ero- 

 sion or partly by each is difficult to determine, but for a mile or more south of Amherstburg 

 it seems certain that the cutting has been done almost entirely by the river, for the shore is 

 not much exposed to lake waves and the current is deep and strong. South of Elliott Point 

 the most recent cutting has no doubt been done by the lake waves, but its amount has been 

 slight. Originally the land here was probably cut out by the, river when the level of the lake 

 stood lower. When the lake stood 10 to 15 feet lower than now, the soundings indicate that 

 the general shore line off Point Mouille and Bar Point must have been half a mile to a mile 

 farther lakeward on both sides. 



If the general trend of the coast line from Toledo to Point Mouille is produced it meets 

 the Canadian shore somewhere near Bar Point, and if the line is curved a little eastward to 

 conform to the general trend of the north shore, it will strike about a mile southeast of Bar Point 

 and will then represent more truly the probable position of the shore line and the configuration 

 of the' land as they would have been if not modified by Detroit River. 



The mouth or estuary of Detroit River may be defined as covering the area which lies 

 between Grosse Isle and Bois Blanc Island on the north and a line joining Point Mouille and 

 Bar Point on the south. It measures about 4 miles each way. There is much reason to believe 

 that this area was originally land, like that now lying to the east and west, and had a sur- 

 face substantially of the same character and altitude. In this area only one narrow channel 

 near the east shore (the present line of navigation) is more than 20 feet deep, the depth over 

 the rest of the area averaging about 10 feet. The bordering land is nowhere over 15 feet above 

 the lake and on the west side is mostly under 5 feet. It is certain that at least a large part of 

 the estuary was land, for Grosse Isle and in fact all the islands in this part of the river and 

 also the banks of the mainland on both sides within the estuary are shown by the distribu- 

 taries and the submerged channel beds to have been carved out of a former land mass by the 

 river. But even granting this, the assumption that the whole area was formerly land may seem 

 unwarranted. 



This conclusion, however, is strongly suggested by the early distributaries. On the east 

 side the distributaries ran away to the south from Amherstburg and one to the southeast from 

 Elliott Point. This they woidd hardly have done if there had been anything like a deep chan- 

 nel running south from their heads on the course of the present river. 



On the west side the distributaries east of Rockwood run south, which they could hardly 

 have done if there had been an available channel between the present shore and Celeron Island. 

 The river soon developed a master stream, or possibly two of them, one between Grosse Isle 

 and Bois Blanc Island and another where the Trenton Channel is now, and these rapidly 

 cut back channels in the relatively soft drift to the resistant rock ledges and bowlder beds. At 

 this time, the level of Lake Erie being somewhat lower than now, the streams on the west 

 side naturally turned southeastward toward it ; and those which turned first had the shortest, 

 steepest courses and drew an increasing proportion of the water to themselves, thus causing 

 the Rockwood channels to be abandoned at a very early stage. It seems certain that these 

 channels would not have been made at all, unless, when the water first rushed over the barrier, 

 there was land with no pronounced channel or depression where the estuary now is. (See p. 491 .) 



In the estuary and along the near-by shores of Lake Erie the bottom is generally stony 

 to a depth of about 15 feet, below which it is mostly sand. Possibly this might be ascribed to 

 the action of the undertow from the surf with the lake standing at its present level, but in the 

 light of other evidence this sand may be regarded as a submerged beach, due to the recent rise 

 of the lake upon the land about all its western shores. Several authors pointed long ago to 

 evidences of such a change, and Moseley (see p. 462) finds that the water has recently risen at 

 least 12 to 15 feet upon the land, thus agreeing very closely with the amount of recent change 

 suggested by the various features of the Detroit River estuary. 



