CHAPTER XI. 

 POET HURON MORAINIC SYSTEM AND PEOBABLE CORRELATIVES. 

 PORT HURON MORAINIC SYSTEM IN HURON AND SAGINAW BASINS. 



By Frank B. Tayxor. 

 GENERAL RELATIONS. 



The Port Huron is a complex system of moraines rather than a single individual, but its 

 component ridges are not so prominent as those of the West Branch-Gladwin group of moraines 

 in the Saginaw Valley. The front ridge seems in most places like a strongly developed single 

 moraine, and for this reason it has in the past been treated as a distinct individual and has been 

 called the Port Huron moraine. It is of the substage order of magnitude and is, in fact, one of 

 the best developed and most clearly defined moraines in the Great Lakes region. 



After the Defiance moraine, which was traced from Ohio into Michigan as far as Adrian by 

 G. K. Gilbert in 1870, the main moraine of the Port Huron system was the first to be distinctly 

 recognized on the east side of the southern peninsula of Michigan. 1 Its relations to the Saginaw 

 Bay and Lake Huron basins and to the intervening ridge of the "thumb" are so simple as to 

 furnish an ideal illustration of the relation of the ice front to the larger elements of relief. On 

 the "thumb," from Caro to Bad Axe and thence southward to Wadhams, it is a typical land-laid 

 moraine, but in the central parts of the Saginaw and St. Clair valleys it is an equally perfect type 

 of water-laid moraine, though when studied in detail it is found to be not a single ridge but a 

 composite system. 



The main moraine of the Port Huron morainic system played a more prominent part in the 

 lake history, so far as that history has been worked out, than any other moraine in the Great 

 Lakes region. The Huron-Erie glacial lakes had a more complicated history than those of any 

 other basin, the principal cause of complexity being the oscillation of the ice front during the 

 general retreat. Where the sequence of retreats and readvances was critically related to the 

 retaining barrier of the lake waters, as it was on the "thumb" of Michigan, every movement of 

 the ice front backward or forward affected the level of the waters. Oscillations of the ice front 

 on the "thumb" of Michigan did not affect the level of the waters in the Saginaw basin, but 

 nearly every movement changed the level of those in the Huron-Erie basin. In the early stages 

 of these waters several changes of this kind occurred, and it has been difficult to unravel the 

 complexities which they produced. 



The main moraine of the Port Huron system marks a pronounced readvance of the ice front 

 and records one of the simplest of these changes, uncomplicated by any later or earlier ones. 

 The ice formed the barrier which retained Lake Whittlesey, and its readvance raised the waters 

 of the lake more than 40 feet, submerging the earlier Arkona beaches. It was in connection 

 with this moraine that the effects of readvance in raising lake waters were first recognized. 



Besides its critical relation to the Huron-Erie lakes, this main moraine is distinguished above 

 the others by having been traced continuously across the Great Lakes region for a greater 

 distance than any other. Mr. Leverett describes its distribution and characteristics at points 

 farther north and west (see pp. 302-315) and the writer has traced it eastward across Ontario 

 into New York. 



Two other fainter water-laid moraines belonging to the Port Huron system he between the 

 main moraines of the system and the shore. The first, the Bay City moraine, surrounds Sag- 

 inaw Bay from Iosco County to northern Huron County. The other, the Tawas moraine, is a 

 fragment which lies near the shore in Iosco and Arenac counties. 



1 Correlation of Erie-Huron beaches with outlets and moraines in southeastern Michigan: Bull. Geol. Soc. America, vol. 8, 1S97, pp. 41-43. 



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