POSTGLACIAL DEVELOPMENT OF CONNECTING BIVEKS OF GREAT LAKES. 481 



the submerged growing parts of the delta between narrow but very ragged and irregular belts 

 of land barely above the mean level of the lake. These form natural levees, broken by man}^ 

 small crevasses through which the water pours into the very shallow bays along the sides. 

 The moment the roily water leaves the deep channel it slackens and deposits the coarser 

 parts of its sediments. Thus the ragged low levees have been built up by the distributaries 

 themselves, and each little crevasse in these levees tends to build its own smaller levees out 

 into the shallow bay into which it enters. These levees in turn are worn away and destroyed 

 by the feeble action of the waves which run in over the shallow bays. 



FRONT OF THE NEW DELTA. 



That growth is at present active in the western part of the delta is shown by the long 

 ragged fingers of the South and Middle channels and the Chenal a Bout Rond, each of which 

 projects its levees about 4 miles bej r ond the general land front of the delta.- The whole area 

 between the active channels and for a mile or more beyond then ends has been extensively 

 built up in recent times and is still actively growing. 



The limits of the newly built delta are clearly shown by the soundings. The new part, 

 which is about 10 miles long from north to south, has been added to the west side of the older 

 delta and projects into the bed of the lake about 5 miles westward from the ill-defined land 

 margin. The 2-fathom (12-foot) contour shows a well-marked reentrant about halfway 

 between the ship canal and the south end of the Bassett Channel. It runs about \\ miles 

 northward into the front of the delta and marks the southeast limit of the newly made part. 

 On the north side the same contour shows a narrow unfilled part of the lake running east to the 

 mouth of Swan Creek from the deeper part of Anchor Bay. The wider, deeper part of Anchor 

 Bay defines the western front. 



CHANNELS OF THE OLD DELTA. 



In the size and character of its channels and in its relatively smooth south front, the old 

 part of the delta east of the South Channel presents a strong contrast to the new part just 

 described. The principal channels in the old part are the Chenal Ecarte and the Johnston 

 Channel, which branches from it, the Blind Channel, and the Bassett Channel. 



These channels, especially the Ecarte and Johnston channels, are very crooked and narrow, 

 being generally not over 400 feet wide. The water is generally 20 to 30 feet deep, but is reduced 

 on bars to 15 to 17 feet. The Blind Channel, which branches from the South Channel a inile. 

 below the head of Russell Island, is more nearly dead than any other that still carries water. 

 At its head it is only 2 feet deep and is very narrow, and through most of its length it is not 

 over 10 to 15 feet deep. An extinct channel, which leaves the river 2 miles above Port Lambton 

 and runs south to the Ecarte a mile below its head, is the oldest known channel of any length. 



The Chenal Ecarte leaves the river 2 miles above Russell Island, and it and the Johnston 

 Channel seem more like artificial canals than natural distributaries. Still, they are of a type 

 common in deltas. They are not intensely active like the North Channel, but seem to have 

 reached a stationary or balanced state, and although half dead and substantially unchanged 

 for a long time, they do not become closed. The Blind Channel has progressed further toward 

 extinction and will probably be closed at a not distant date. 



The Bassett Channel, which branches from the South Channel at the great westward bend, 

 is a dying distributary. Its deep part is not wider than the Ecarte, but for 2 miles down from 

 its head it is bordered on one side or the other by shallows 400 to 800 feet wide. This channel 

 has not progressed so far toward extinction as the Ecarte, which was once large like the South 

 Channel of to-day but has become gradually contracted and now has scarcely any shallows 

 along its sides. Water plants, such as sedges and rushes, are important agents in the con- 

 traction of these channels, when once they begin to decline. The plants slacken the roily waters 

 34407°— 15 31 



