18 PROCEEDINGS OF THE XATIOXAL MUSEUM vol.76 



At present there are too few occurrences of the '' Blue Shale " known 

 to be able to state definitely the amount of variation in its thickness 

 nor to what cause this variation is due. It is now known to range 

 between 6 and 11 feet at different localities. The upper surface 

 wherever seen is slightly undulating; but whether this undulation 

 was caused by sub-aerial or sub-marine erosion it is impossible to 

 determine with the information now at hand. 



The sudden introduction in the Charlevoix stage of an entirely new 

 and un2:)recedented set of physical and litliological conditions is in 

 itself sufficient to make one suspect an erosional break at its base. 

 Throughout the first 2 or 3 feet (in some places gi'eater, see locality 

 13), of beds in the initial Charlevoix deposition, wherever seen, 

 there is a considerable abundance of fine, rounded quartz grains 

 interspersed more or less evenly through a granular reworked matrix 

 containing numerous worn and broken shell fragments. As a whole 

 the Charlevoix series is characterized by fragmental deposition 

 throughout, frequent occurrences of bituminously laminar beds, the 

 presence of a coarse, calcareous oolite near the middle of the section, 

 and the recurrence of fine grained beds at the top. 



The most interesting physical feature of the Charlevoix is. how- 

 ever, the character of its upper surface. For a study of this phenom- 

 enon the reader is again referred to the inset on Plate 2 and the 

 geological section taken at localitv 13. 



At the Curtiss quarry (locality 13), a section through the entire 

 thickness of the Charlevoix stage may be taken and here also may be 

 seen the highest beds belonging to this division visible anywhere in 

 the district. The thickness of this series from the base of bed 1 to 

 the top of bed 9 is slightly short of 28 feet. The preceding beds 

 comprise the Charlevoix series in their greatest preserved develop- 

 ment. In the face of the quarry, running in a northwesterly direc- 

 tion, these beds are cut in downward succession by a distinct and 

 pronounced, irregular, angular unconformity. Evidence points to 

 a considerable time interval during which there was much erosion of 

 the Charlevoix series. During the emergence, at various places and 

 in particular the west end of the locality 13 quarry and west along 

 the present lake shore, beds 9, 8b, Sa, 8, 7, 6, and a few feet of the 

 preceding " Pelecypod-Gastropod Bed," bed 5, were in some places 

 partially, in others completely, removed by erosion. This, like most 

 of the quarries in the region, is situated in the center of a longitudinal 

 dome or anticline, and it is probable that during the post-Charlevoix 

 emergence the beds were domed and then subjected to an irregular 

 penepLaning effect. Accompanying this folding was a slight read- 

 justment by faulting which is well exhibited in the south face of the 

 ^quarry. This fault has a vertical throw of about 6 inches which does 



