CHAPTER IV. 



General Observations — Table of Geological Formations - 



Many interesting considerations present themselves on a 

 general review of the geology of the peninsula. From the Lake 

 Superior Sandstone to the close of the Helderberg period, our 

 State seems to have had a common history with Canada West, 

 and the States on both sides of us. The same groups of rocks 

 are traced uninterruptedly from New York across the peninsula 

 of Canada to Michigan, and even to the Mississippi river, pre- 

 serving throughout that whole extent as great a degree of 

 palseontological identity as could be expected of faunas stretch- 

 ing over somany degrees of the earth's surface. It is true, as 

 has been long since shown by Prof. Sail, that nearly' every 

 member of the Silurian and lqwer Devonian . systems, thins 

 gradually in its westward prolongation, loses somewhat of its 

 arenaceous or argillaceous character, and becomes at the' west 

 much more calcareous — changes which have generally been 

 regarded as proving the origin of the materials of those groups 

 to have been at the east. It is interesting to observe, however, 

 notwithstanding this westward attenuation, how completely we 

 are able to recognize all the essential features of the New York 

 System in our own State. 



From the close of the Selderberg period, on the contrary, 

 Michigan has had a history to some extent peculiar. The 

 rocks of the Hamilton group can indeed be traced almost con- 

 tinuously from New York into our own State, but the palajon- 

 tological characters are found materially changed, and the 

 strata are more argillaceous. The Portage Group, of New 

 York, supposing it to be represented by our Huron group, has 

 received great accessions of argillaceous matter, and seems to 

 have been deposited under circumstances more unfavorable to 



