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. 



The scarcity of gravel in all the later ridges and the valle3^s 

 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 bv 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 



