STATE GEOLOGIST. 137 



the same direction. They constitute evidences that the mate- 

 rials for our upper Devonian and carboniferous rocks have been 

 derived from the north. The Helderberg limestones are 350 

 feet thick at Mackinac, and not more than 60 feet thick in Mon- 

 roe county. The Hamilton Group, so well developed in Thun- 

 der and Little Traverse Bays, is not recognized in the southern 

 part of the State. The Huron Group with its gritstones and 

 flagstones at Pt. aux Barques, contains only two strata of 

 flagstone at Grand Eapids. The conglomerate at the base of 

 the Marshall Group, at Pt. aux Barques, is recognized at none 

 of the southern outcrops. The pebbles scattered through the 

 Marshall and Napoleon Groups in Huron county, are entirely 

 wanting in Jackson and Calhoun counties; while, on the con- 

 trary, extensive patches of the Marshall sandstone are found 

 finely cemented by calcareous matter at Battle Creek, Joncsville 

 and other southern points. 



If our later palaeozoic rocks are entirely isolated from those 

 of adjoining regions; if their lithological characters are differ- 

 ent; if their organic contents are peculiar; if their materials 

 have been received from another direction; what prevents us 

 from saying that Michigan has had a little geological history of 

 her own, that her boundaries were marked out many thousand 

 years ago — in short, that she was the very first of the States to 

 take her place in this great and imperishable Union. 



One other remark is suggested by this review ef our rocks. 

 The geology of Michigan discloses little connection between 

 the Carboniferous Limestone and the Coal Measures; while the 

 transition to Devonian rocks is imperceptible. I see no reason 

 for drawing the broad lines which separate great systems, 

 between the Marshall and Napoleon groups, or between the 

 Napoleon group and the Carboniferous limestone. On the 

 contrary, I see this limestone characterized by a peculiar, per- 

 sistent, marine fauna, while the Parma Sandstone, the Coal 

 Measures and the Woodville Sandstone, were accumulated in 

 shallow waters near shores, or even in marshes; and are char- 



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