478 PLEISTOCENE OF INDIANA AND MICHIGAN. 



surf-wasted zone lie near, unless buried under the lake clays. Even if such a zone be present, it 

 is more than 20 feet below the ridge crest and can not be accredited to the waves of so small a 

 lake. On the other hand, these characteristics of situation, trend, composition, and height of 

 the ridge with parallel depressions or flats on the two sides are characteristic of eskers. The 

 feeble waves of Lake St. Clair in the time of Lake Algonquin may have in some degree fash- 

 ioned the gravel along its crest, but they could have done nothing more. 



This gravel ridge, as already stated, lies along the central axis of the St. Clair Valley. At 

 the time of Early Lake Algonquin it divided the bed of the river southward from St. Clair into 

 two channels of probably nearly equal capacity. They appear to be troughs associated with 

 the esker. The river at this stage endured through the time of Early Lake Algonquin and the 

 early part of the third or Port Huron-Chicago stage — long enough for Lake St. Clair to build a 

 distinct though not strong shore line and for the river to accomplish a well-defined work of 

 erosion and deposition. It seems certain that during this early stage of the river the part of its 

 bed which lay east of the esker became deeper than that which lay west, so that later, when 

 Lake St. Clair fell to a lower level, the river abandoned the western channel and became 

 concentrated in the eastern one, in which it now flows. 



ST. CLAIR DELTA. 

 SOURCE AND CHARACTER OF MATERIAL. 



The delta of St. Clair River in Lake St. Clair is exceptional from the fact that it was biu'lt 

 by the outlet river of one of the Great Lakes and by water generally supposed to be clear and free 

 from sediment. (See fig. 11.) 



The peculiar relation of St. Clair River to Lake Huron has been the chief cause for the 

 formation of the delta. Storm waves on the south shores of Lake Huron have done and are still 

 doing a tremendous work cutting away the bordering lands, in some places cutting back 5 to 6 

 feet a year, as established by measurements and surveys. 1 



The storms that do the most effective work on these shores come from northerly direc- 

 tions and tend strongly both by oblique wave action and by wind-driven currents to carry the 

 sediments derived from the cutting toward the south end of the lake. The same thing occurs 

 in Lake Michigan where there is no natural outlet and where the sands have consequently 

 accumulated in enormous quantities as dunes about its south end. Storms make the water 

 of Lake Huron roily all along the shore and for some distance out into the lake. St. Clair River 

 opens from the southern extremity of the lake and the roily water is carried into the river and 

 down to Lake St. Clair. Here, on meeting the still water, the finer sediments are deposited, 

 and it is mainly through a long continuance of this action that the delta has been built. A 

 considerable amount of sand and some gravel also are rolled along the bottom and are added to 

 the delta deposit. 



An excellent detailed study and discussion of the St. Clair delta was made by Cole 2 for the 

 Michigan Geological Survey. His investigations show the delta to be in nearly all respects a 

 normally formed, low-grade (fine sediment) delta, though having some peculiarities and some 

 exceptional features. Cole made 31 borings in the delta and found clay of varying quality 

 to be the main constituent, with considerable quantities of sand and sandy clay. At a certain 

 depth, generally 12 to 17 feet, the borings penetrated a stiff blue clay which in a few feet became 

 soft and waxy and continued uniform in texture to an indefinite depth, in one boring to at least 

 56 feet. Borings at Algonac and Port Huron show this "bottom clay," as Cole calls it, to be 80 

 to 100 feet deep at Port Huron and 150 to 200 feet deep at Algonac. In several borings, at a 

 depth of 11 to 12 feet below the level of Lake St. Clair, Cole found beds of muck composed of 

 decayed vegetation resting on the stiff top layer of the "bottom clay." 



i Gordon, C. H., Wave cutting on west shore of Lake Huron: Ann. Rept. Michigan Geo]. Survey, 1901, pp. 2S3-290, Pis. XI-XV. 

 2 Cole, L. J., The delta of the St. Clair River: Michigan Geol. Survey, vol. 9, pt. 1, 1903, pp. 1-25. 



