DESCRIPTION OF THE FORMATIONS. F\ 45 



parts of the State and in other States. Included by Prof. 

 Rogers in his No. Y, they became a local group. All com- 

 parison and correlation with the previously named rocks of 

 New York being avoided, the whole of this No. V, for rea- 

 sons which do not appear to be satisfactory, lias often been 

 considered the equivalent of the Clinton group of New York. 

 On this view the vast mass of shale of which they consist 

 (nearly half a mile thick in Perry county) must represent 

 the thin mass of shales and limestones with iron ore, only 

 80 feet thick, on which Prof. Hall conferred the name of 

 the Clinton group. To find a great enhancement of thick- 

 ness in Pennsylvania is common ; but the difference here is 

 excessive and may well make one hesitate before accepting 

 it. Moreover, the great difference in color of the upper part 

 of this No. Y is sufficient to cause a suspicion. The lower 

 portion sufficiently resembles the beds in New York ; but the 

 upper consists of a vast mass of red and variegated shale 

 which has no correspondence to the New York series. 



The extent of its area prevented my making as satisfac- 

 rtoy an examination of this group as I desired, and the 

 material obtained is yet far from being worked out, but the 

 results already deduced from my observations and collec- 

 tions have led me to propose a different arrangement of 

 the beds which have hitherto been assigned to the Clinton 

 group. This arrangement must, however, be regarded as 

 only provisional, and subject to alteration as further study 

 may bring to light new data for the determination. 



I propose to include in the Clinton rocks of Perry county 

 only the lower part of those which have been hitherto re- 

 ferred to For. No. Y. Clear physical partings exist at two 

 or three horizons in the mass. These may be fairly assumed 

 to indicate considerable changes of mode of deposition and 

 of animal life. One of these is the cessation of green 

 smooth shales, and the commencement of bright red sliale. 

 This is a most conspicuous plane of distinction. Another 

 occurs at a short distance below this on the top of the sand- 

 xein ore bed, over which lies a mass of green shale in part 

 calcareous. 



This ore bed, which forms a very constant horizon over its 



