GLACIAL LAKE AEKONA. 375 



ALTITUDE OF THE BEACHES. 



In the Ann Arbor quadrangle the Arkona beaches have altitudes of about 708 to 710 feet 

 for the highest ridge, 700 to 702 for the middle, and 694 to 696 feet for the lowest. This is in 

 the area of horizontality. These altitudes continue for a few miles north of Birmingham, 

 beyond which the beaches rise toward the northeast. Near Croswell the measurements are all 

 by aneroid barometer. At this place beach A has an altitude of about 755 feet, the first beach 

 about 747 feet, and the second beach about 740 feet. The third beach is not represented there, 

 but in Grant Township it is 9 or 10 feet below the second ridge. The first beach rises about 37 

 feet, the second beach about 30 feet, and the third beach about 20 feet. Thus the vertical 

 interval between the first and third Arkona beaches is 14 to 16 feet in the area of horizontality, 

 but increases to about 27 feet in the vicinity of Applegate. This northward increase of vertical 

 interval seems to show a slight movement of uplift while the Arkona beaches were being made. 



In Ohio and eastward, within the area of horizontality, few accurate measures of altitude 

 on the Arkona beaches are at hand. They are so faint that they are not used as roads to any 

 extent, and the topographic maps show no altitudes that are certainly on the crest. The upper 

 one is a little above 705 to 708 feet where measured and the lower one 8 or 10 feet lower. East- 

 ward, from Cleveland, they rise at first gently and then, north of Silver Creek, N. Y., at the rate 

 of about 2 feet to the mile. At Alden the upper beach is about 865 feet above sea level and the 

 lower about 10 feet lower, indicating a rise of about 155 feet from the area of horizontality. In 

 Ontario the altitude southwest of Clinton is about 745 feet (aneroid). It is not yet known 

 certainly which one of the Arkona ridges it is that is so strong in the Au Sable Valley, but it is 

 not the highest. This indicates a rise of 30 to 35 feet. The greater rise in New York appears 

 to be due to the greater distance of that locality from the area of horizontality in the direction 

 of uplift. 



From what is now known it appears that the Arkona, Whittlesey, and Warren beaches 

 all rise together at nearly the same rate in both the western and eastern districts. The great 

 uplift came after the making of those beaches; only a slight uplift had occurred before, as 

 recorded in the Maumee beaches. 



In some respects, especially in the matter of beaches modified by submergence, Lake 

 Arkona is the most remarkable of the glacial lakes. Lake Maumee had a similar though briefer 

 history during the making of its lowest and middle beaches. 



GLACIAL BARRIERS. 



Lake Arkona, which was about three times as large as the present Lake Erie, existed during 

 the pause after a recession of the ice front and before a readvance. The lake was held in bj T 

 two ice dams, one stretching across the south part of the Lake Huron basin and the other across 

 the west end of the Lake Ontario basin. The readvance of the ice which ended Lake Arkona 

 and raised the Huron-Erie waters to the level of the Whittlesey beach affected both of the ice 

 dams, and as a consequence both of the correlative moraines and all the beaches leading up to 

 them were partly overridden and obliterated. 



It is therefore to some extent a matter of conjecture as to where the ice barriers to Lake 

 Arkona stood, though both may be located somewhat closely. The very considerable strength 

 of the Arkona ridges at their north terminal points on the two sides of the "thumb" seem to make 

 it necessary to suppose that when these ridges were made the ice front was at least 25 miles away 

 on lines at right angles to the general trend of the shore. The character and relations of the 

 Arkona ridges at Alden, N. Y., and still more of those near Clinton, Ontario, bear out this con- 

 clusion. The facts seem also to favor a relatively long duration for Lake Arkona, according 

 well in this respect with the idea that the readvance to the Port Huron morainic system was a 

 movement of more than minor importance. 



