466 JAMES WALTER GOLDTHWAIT 



away among the moraines. Those beaches which locally show 

 strong development cannot be grouped into a single system of diverging 

 planes hke the Algonquin beaches presently to be described. The 

 rate of inclination from south to north is hardly one foot per mile. 

 It is possible, then, that the southward slant of these beaches is due 

 wholly to ice attraction, according to the calculations of R. S. Wood- 

 ward.' Assuming an ice sheet of reasonable extent and thickness, 

 Woodward found that its attraction might be sufficient to raise the 

 surface of the lake nearby into a curve, concave upward, with an 

 apparent inclination of several inches to the mile for the first fifty 

 miles or so from the ice border. If this be the right explanation for 

 the Lake Chicago beaches north of Grand Haven, it accounts for the 

 apparent lack of harmony between the measurements; for the 

 relation of successive water planes to each other would be similar 

 to the branchings of a feather (see Fig. 2) and the few points where 



Fig. 2. — Diagram showing how a series of ice-attracted water planes might look, 

 in profile. 



measurements have been made might happen to lie on several dif- 

 ferent divergent surfaces. If, on the other hand, the northward 

 ascent of the beaches is due to a series of differential uplifts of the 

 region, these uplifts must have occurred before the formation of the 

 next lower beach, the "Algonquin" beach, for that beach is horizontal 

 over the whole southern half of the Michigan basin. 



North of Ludington little is known of these beaches, and no meas- 

 urements have been made. While the Glenwood and Calumet shore 

 lines might expectedly terminate at any place, against a moraine, 

 the Toleston or lowest shore line of Lake Chicago ought to extend 

 northward to the place where the ice border first uncovered a low 

 pass leading across Michigan into the adjoining Huron basin, probably 

 east of Little Traverse Bay. No traces of such a beach are known. 

 It is probable that the record is too weak and obscure to be recog- 

 nized. 



I R. S. Woodward, "On the Form and Position of the Sea Level," U. S. Geol. 

 Surv. (Bull. 48. p. 88), 1888. 



