CHAPTER IV. 



ions — I on* 



Many interesting considerations present themselves on a 

 general review of tl ry of the peninsula. From the Lake 



Super • i to the cli >e of the Ilelderberg period, our 



.s to have had a common history with Canada West, 

 and the $ .»n both sides of us. The same groups of rocks 



are traced uninterruptedly from New York across the peninsula 

 Michigan, and oven t<> the Mississippi river, pre- 

 serving- throughout that whole extent as great a degree of 

 ,1 identity as could be expected of faunas stretch- 

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

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

 member of the Silurian and lower Devonian systems, thins 

 gradually in its westward prolongation, loses somewhat of its 

 us character, and becomes at the west 

 much eons — cl . liieh have generally 



- proving tin- origin of the materials of those groups 



to havi b< i east [t is interesting t .however, 



notwil v ird attenuation, how completely we 



t: essential f( itures of the Now York 



:n in our 



f the Helderberg period, on the 

 M had a history to Bome extent peculiar. The 



Hamilton e I be tra< I con- 



ur own State, 1 ut tl 



illy chai ' the 



New 



'i 1 by our Hui >, has 



i re unfa 1 



