.ART. 14 MICHIGAX TRAVEKSE GROUP POHL 19 



jiot continue into beds of the Petoskey formation although it can be 

 'Easily traced through all the members of the Charlevoix. This can 

 jiot be explained on the basis of incompetency, for if anything the 

 beds of the Charlevoix are more competent than those of the Petoskey. 

 INor can it be dismissed by an argument based on '' cushioning " for 

 the basal beds of the Petoskey are compact and easily fractured. As 

 if to further substantiate the importance of the unconformity there 

 is a complete change of faunal and lithological characters above the 

 break. In a series of small quarries, bluffs, and ledges near water's 

 «edge, forming a continuous exposure of a mile in length to the east 

 of locality 13, the contact between the Charlevoix and the Petoskey 

 series is exhibited at an almost constant height above lake level 

 throughout the length of the exposure. The crinoidal Cyrtina- 

 Oypidula zone of the Petoskey here rests on the irregularly eroded 

 .surface of one or another portion of the Pelecypod-Gastropod bed 

 {bed 5) of the Charlevoix. We may thus see that the removal of 

 beds from the top of the Charlevoix stage was not of restricted 

 -character, for over considerable distances there is a known deletion 

 hy erosion of between 12 and 15 feet. It is extremely probable tliat 

 «ven greater thicknesses were deposited during Charlevoix time and 

 subsequently denuded, but to what vertical extent can not be 

 ^ascertained. 



The acceptance of the proof presented requires not only the with- 

 drawal of the sea at the end of Charlevoix deposition, but also the 

 •emergence of the area for the minimum time necessary for the con- 

 :Solidation of the beds and for the removal of at least 15 feet of mostly 

 tough limestones, before the earliest local encroachment by and 

 •deposition in the Petoskey sea. 



This contact is again shown to excellent advantage in two other 

 .sections and since the importance of this phenomenon can not be 

 .underestimated it would be better to include a discussion of their 

 peculiar characteristics here. 



In a now abandoned quarry (locality 15), nearly 2 miles west 

 of locality 13 on Nine Mile Point (near center sec. 2, T. 34 N., K. 7 W., 

 ■Charlevoix County), bed 9 of the Charlevoix stage again exhibits the 

 effects of erosion. This bed is here composed of a massive white 

 limestone with numerous solution cavities, probably due to leaching 

 •contemporaneous with the pre-Petoskey denudation. This highest 

 member of the Charlevoix section is deeply gutted and channeled, 

 and the initial deposit of the Petoskey, a course shale about three- 

 •quarters of an inch thick, rests on the unevenly eroded surface of 

 the beds beneath. The filling of the irregularities in the underljang 

 :series is completed by a fragmental, shaley limestone carrying over- 

 turned heads of a small-pitted ^troviatopora and broken Gypidula 



