GEOLOGICAL AND NATURAL HLSTORY SURVEYS. 173 



tails to his description of this formation in his report of tiie pre- 

 ceding year, he gives here only some of its economical adaptations, 

 suggesting that some of the strata occurring near Monroe may be 

 suited for a hydraulic lime; and he instances for selection the dark 

 blue and the vesicular or volitic strata. He makes additional ref- 

 erence to sand suitable for glass making, which constitutes a .stratum 

 through the middle of the formation. 



The kidney iron formation is well described and its northern 

 limits traced. It is recognized as immediately underljdng the fer- 

 ruginous sandstone. 



The " fossiliferous ferruginous sandstones," since embraced in the 

 "Marshall group," are ranked as "Carboniferous," though, as he 

 says, they all occupy a position below the lowest of the coal beds. 

 This sagacious determination by Mr. Hubl)ard is particularly to be 

 noted, since the same strata were afterwards for many years on very 

 plausible grounds indentificd Avith the Chemung sandstones of 

 southern New York. Mr. Hubbard gives a stratigraphical table of 

 seven subdivisions. The uppermost sandstone he pronounces a good 

 material for grindstones, and for such use it has subsequently been 

 employed to a large extent. It is the so-called " Napoleon Sand- 

 stone." The "yellow fossiliferous sandrock" holds a lower posi- 

 tion. The formation shows a slight northerly dip, and its whole 

 thickness " below the lowest of the beds, whicli embrace coal plants, 

 will be found to exceed IGO feet." 



Under the head of "Tertiary and diluvial deposits" Mr. Hubbard 

 refers to evidences of currents of a universal ocean sweeping from 

 the north. He refers to the " diluvial furrows and scratches on the 

 surface of the limerock, to bowlders of primary rocks, and even 

 masses of native copper, whicli he truly says are no evidence of 

 beds or veins of copper in tlie vicinity. The blue and yellow clays 

 immediately overlying the limerock of Monroe County, and bor- 

 dering Lakes Erie and Michigan, are regarded as older than the 

 diluvial deposits consisting chiefly of sand and gravel. 



Mr. Hubbard refers, like Mr. Douglass, to "large fragments of 

 limestone occasionally to be met with, which liad been disrupted from 

 the transition and carboniferous rocks of the Peninsula. The largest 

 masses of these were found near the summit of the great dividing 

 ridge on its eastern declivity. Several masses in the town of Som- 

 erset, Hillsdale County, are of such extent as to be easily mistaken 

 for rock in place, portions only being visible from beneath the im- 

 bedding diluvium. I became convinced, however, by tlie associated 

 fossils that they belong to an older formation than the carboniferous 

 rocks of tlie vicinitv. Bowlders of this rock arc so numerous in some 



