476 PLEISTOCENE OF INDIANA AND MICHIGAN. 



GRAVELLY RIVER BARS SOUTH OF ST. CLAIR. 



The concentration of the river in one channel north of St. Clair led to rapid downcutting 

 through the soft materials of the moraine. At first the water evidently went through the gap 

 with a rush and emerged on the flat plain south of St. Clair, where it spread in a relatively thin 

 sheet 3 or 4 miles wide. Here it slackened and deposited long bars of gravel which it had washed 

 out of the moraine and out of the newly excavated river bed to the north. All the gravel knolls 

 and ridges south of St. Clair, however, are not of this description; a large ridge extending a mile 

 southward from the Pine Kiver bridge and another lying in central sec. 12, China Township, 

 appear to be glacial. 



The river bars lie east of the large glacial ridges, mainly in East China Township. They 

 trend a little west of south, several of them being cut off at their heads by St. Clair River, which 

 here runs south-southeast. One bar begins a little south of the Oakland Hotel and another 

 nearly a mile farther south, near where the electric railroad turns west from the river bank. 

 Two others run south from the bluff in sec. 18,East China Township. The bars have long, smooth, 

 tapering forms and are a quarter of a mile to a mile in length, 2 to 6 feet high, and not over 

 300 feet wide. They are composed of sandy gravel and small pebbles, resting on clay, and are 

 unmistakable river bars. A number of still smaller, shorter swells of sandy gravel of the same 

 origin and trend are too small to be shown on the map. It seems probable that all of the bars 

 were formed mainly during the active cutting of the river through the moraine rather than later 

 when the channel had been completed and rapid cutting had ceased. 



OLD RIVER BED SOUTH OF ST. CLAIR. 



After quickly cutting through the Port Huron moraine the river reached a relatively stable 

 state as the outlet of Early Lake Algonquin with a descent of about 10 feet from Lake Huron 

 to Lake St. Clair. The Algonquin beach is 605 to 607 feet above sea level or, on the average, 

 about 25 feet above Lake Huron, its level being determined mainly by obstructions in the lower 

 part of Detroit River. (See p. 495.) 



St. Clan* lies mainly on a bench or terrace 10 to 12 feet above the river. The present river 

 flows almost due south, but a steep bluff at the back of the terrace runs southwest for about a 

 mile from the bank of the river at the north end of the village. The bluff is nearly 40 feet high 

 in the village, but along the river to the north it rises steeply to over 55 feet above the water. 

 Its highest point is about 1 \ miles north of the village, just opposite the narrowest, deepest, and 

 swiftest part of the river — the place where the river cuts through the main moraine of the Port 

 Huron morainic system. 



On emerging from its constricted passage through the moraine the river of the Early Algon- 

 quin stage entered abruptly on a wide, low plain. Evidently a strong current of the spreading 

 river pushed southwest over the site of the village and cut into the moraine, makmg the con- 

 spicuous terrace and the high bluff behind it. The first of the large gravel ridges forms the promi- 

 nent knoll just south of Pine River and west of the Oakland Hotel, and the flat between this 

 and the bluff in the southwest part of the village is part of the abandoned river bed of that time- 

 This runs southwest through sees. 1, 11, and 12, China Township, turns directly south to the 

 middle of sec. 24, bends a little to the west, and continues in a straight line to west of Roberts 

 Landing, south of which it gradually fades away on the low sand-covered clay plain. In St. 

 Clair it is from one-third to one-half mile wide, but farther south it is three-fourths of a mile to a 

 little more than a mile in width. 



On entering the old river bed Pine River turns abruptly from southeast to northeast. A 

 short distanco south of the bend the floor is about 15 feet above St. Clair River, and it declines 

 very gradually southward to 3 or 4 feet above the river west of Algonac. The floor was origi- 

 nally nearly all a swamp and a considerable part is so still. The banks are rather peculiar; below 

 Pine River they show very little evidence of scour by the old river. The west bank appears to 

 be a cut bluff in some places, but the cut is now obscured by fine sand which forms a narrow, 



