SANDUSKY BAY AND CEDAR POINT 235 
we get a rate of 2.1 feet per century, which closely approximates 
the rate obtained by comparing the others with Ridge 6. It is 
quite possible that Ridge 3 is older than I have estimated. 
On some of the recent ridges are aqueous deposits at a higher 
level than that at which the main roots join the trunks of the 
trees, indicating that the ridge was not the work of a single 
storm. If these deposits were left long after the trees started 
they would vitiate the results shown in the table. I have found 
no evidence that they were left long after and in the case of 
Ridges 2 and 6, it is certain that they were not, because new 
ridges were soon formed in front of each. The percentage of 
probable error in the determination of the age of Ridge 2 is less 
than in the other old ridges. It is old enough to give a long time 
interval. The rate based on comparing it with Ridge 6 is near 
the mean of the rates based on other comparisons. For several 
reasons then it may be regarded as the best. 
RATE OF SUBSIDENCE OF THE LAND BASED ON A COMPARISON OF 
HEIGHTS AND AGES OF OLDER RIDGES WITH RIDGE 6. 
Number |Maximum h’ght|Approx- | Older Lower |Change of level 
of of aqueous imate | . than than feet per 
Ridge deposits, feet jage, 1904| Ridge 6 | Ridge 6 century 
1 2.66 475 430 | 9.47 2.20 
2 4.55 400 SE Tl ies! 2.14 
3 5.4 FIORE 2Gor ilieGane 2.54 
| 
5 9.4 180 Loe eo 2 O23 
6 WPA 1b) 45 
| 
The scarcity of gravel in all the later ridges and the valleys 
between them is in marked contrast to its abundance in and 
between the older ones. Ridge 4 and those more recent contain 
but little gravel; ridges 6, 7 and 8, probably not a hundredth part 
as much as ridges 1 and 2. It is scarce also along the present 
lake beach, but on the bay shore the old gravel deposits have been 
exposed by recent erosion. When the older ridges were formed 
the hardpan overlying the rocks of the Dune Section and con- 
taining an abundance of pebbles and boulders was in reach of 
the waves; but when the later ones were formed the lake had 
attained a higher level and the hardpan was too far below the 
