406 PLEISTOCENE OF INDIANA AND MICHIGAN. 



" seems to be quite horizontal in its course around the ' thumb' " seems incorrect. The facts now 

 in hand show that the Warren beach rises about 100 feet from the area of horizontality to its 

 highest point northeast of Bad Axe, and also that the uplift which tilted and split the Grass- 

 mere and Lundy beaches amounted altogether to nearly 100 feet at the north line of Sanilac 

 County. 



The relations in Sanilac County show clearly that the uplift which raised and tilted the 

 Wayne and Warren beaches occurred after the formation of both these beaches and before the 

 formation of the Algonquin beach. The Grassmere and Lundy beaches fill the interval both 

 in time and space and their tilting and northward splitting is in close accord both in amount 

 and distribution with the uplift of the Warren beach. 



In view of these facts it seems certain that these beaches descend southwestward along 

 with the Warren beach on the west side of the "thumb," just as they ascended northward with 

 it on the east side. 



Lane suggests that the Grassmere beach passes above the head of the Grand River outlet 

 channel, affording an outlet for Lake Lundy in that direction. But if the writer's results are 

 correct, the head of that outlet is within the limits of the area of horizontality and the Grass- 

 mere beach falls a trifle below it; and further, if the writer's tracing and measurements of alti- 

 tude are correct, the upper strand of the Grassmere descends from about 720 feet altitude 

 about a mile east of Grassmere village to about 680 feet about 4 miles east of Reese in Tuscola 

 County. 



So far as known to the writer, there is no locality in the Great Lakes region so favorable 

 as this for the study of the effects of progressing differential uplift on beaches then being 

 formed. But such a study, to attain the best results, requires careful tracing of the individual 

 beaches and accurate measurements of their altitudes at short intervals of distance. The 

 area in which such work should be done comprises Sanilac, Huron, and Tuscola counties. 

 Such a study on the Grassmere and Lundy beaches in these counties gives promise also of very 

 valuable results bearing on the time factors involved and hence on the determination of the 

 rate of deformation or uplift, for this uplift of 100 feet or more occurred while these two beaches 

 were being formed, and is definitely limited in time to the interval between the close of Lake 

 Warren and the beginning of Lake Algonquin. 



In discussing the sand ridges and beaches of Bay and Saginaw counties, referred to above, 

 Cooper generally assumes horizontality, although continuous tracing was not done. The 

 southern part of the arela which he discusses lies in the region of horizontality for all the beaches, 

 and more of it for the lower beaches. But the higher beaches of Bay and Gladwin counties can 

 hardly be horizontal, when the upper Arkona rises from about 710 feet 2 miles northeast of 

 Elsie to 815 feet 6 miles northeast of Gladwin. 



GLACIAL BARRIERS OF LAKE LUNDY. 



The precise location of the ice barriers of Lake Lundy is not known. It seems necessary 

 to infer the presence of an ice barrier on the middle slope of the highlands west of Alpena, for 

 if there was an outlet northwestward for the Grassmere stage of Lake Lundy along that slope it 

 would have continued to carry off the discharge during the time of the Lundy beach, which 

 is about 20 feet lower, but this it did not do. (See also pp. 399-400.) 



On the other hand, any ice barrier near Syracuse, N. Y., must also have rested at a certain 

 definite place on the face of the northward-sloping escarpment. As already stated (p. 399), 

 Fairchild identifies the Marcellus channel southwest of Syracuse as the outlet of Lake Lundy 

 (Dana), but the correlative position of its front has not yet been determined. In the Niagara 

 region the indications are that the barrier of Lake Lundy stood somewhere between the Niagara 

 escarpment and the present shore of Lake Ontario. Thus, while the precise positions of the 

 barriers are not known in Michigan or New York, they must have been within very narrow 

 zones in each locality. 1 



> See fig. G, p. 370; also, Niagara folio (No. 190), Geol. Atlas XJ. S., U. S. Geol. Survey, 1913, p. 18. 



