298 Dr. John T. Plummer on the 



slidden upon each other so as to have left these stria,. I antici- 

 pate a number of grave objections to this conjecture ; but per- 

 haps a re-examination of all the premises, will diminish the in- 

 credibility which may appear to be attached to it, and ultimately 

 lead to the conviction, that the evidences in its favor outweigh 

 those which are opposed to it. At present, I shall leave the sug- 

 gestion without support, reserving such arguments as seem to me 

 to favor it for a more suitable occasion, if such should be given. 



So far as I have learned, the grooves found at this place are 

 the first that have been descried in the blue limestone of the 

 west. And I may here remark, that while removing the super- 

 incumbent mass from this rock, I exposed a large pebble which 

 was flattened and scratched on one side, as if it had been drawn 

 with great weight over some hard surface. 



Leaving the blue fossiliferous limestone, which has so long 

 detained us, we will pass to the superimposed formation, well 

 known at the west, as 



The cliff limestone. — By turning to fig. 1, it will be seen that 

 this rock makes its appearance at four different places in this 

 vicinity, the most distant locality marked being six miles from 

 this town. In two of these places the cliff rock is seen resting 

 upon the blue limestone, the line of demarkation being very 

 obvious. 



This formation consists in general of a much lighter colored 

 rock than the subjacent deposit ; being a pale gray, or yellowish 

 or dull white. It is of very variable texture and hardness ; some- 

 times it is much preferred for macadamizing to the blue lime- 

 stone ; in other localities it is wholly unfit for this purpose. I 

 have had it pointed out to me in one or two places in Ohio as 

 pure sandstone ; sixteen miles from this town, as in other locali- 

 ties, it is found free from fossils and compact as marble ; and again, 

 we find it almost an aggregation of shells. I have seen it when 

 broken often as resplendent as mica ; and I have seen it granular 

 and so darkly stained as to take away all lustre. Its stratifica- 

 tion is no less various than its physical properties. Sometimes it 

 is in thin and broad layers, and furnishes excellent flagstones ; 

 sometimes it occurs in coarse lenticular masses, then in large, 

 thick blocks ; and again, as our most valuable building stone. 

 This last form of it is frequently slightly impaired in quality by 

 the presence of small cubes of sulphuret of iron, which, decom- 



