4 HISTORICAL GEOLOGY OF MICHIGAN. 



We quote from Prof. A. Wiucliell, formerly the State geologist of Michi- 

 gan, the historical geology of this State, as follows: 



The first land witliin the limits of the State was that which we have 

 mapped as Laurentiau and Huronian — a small portion of the Upper Penin- 

 sula, lying northwest of Green Bay. No j^art of the existing continent is 

 older, while nearly all other portions were still sea-bottom, except an 

 angulated belt north of the great lakes and the river St. Lawrence. This 

 original area has been subjected to a vast amount of subsequent invasion, and 

 correspondingly diminished in its elevation and contracted in its dimensions. 

 Its upheaval marked the close of Eozoic, and the dawn of Palaeozoic time. 



At the end of the first period of Palaeozoic Time, an igneous outburst called 

 into existence Keweenaw Point, the Porcupine Mountains, and the interven- 

 ing copper ranges, together with Isle Royal and limited areas upon the 

 immediate shore of Lake Superior. 



After this time there were no local disturbances of special importance. 

 The whole continental mass east of the Rocky Mountain region was, by 

 degrees, bodily uplifted. The Michigan region slowly emerged. The valley 

 which was to become the basin of Lake Superior was at first a bay of salt 

 water. With the progress of continental upheaval, it became isolated fr^m 

 the sea, and was for ages a salt lake. The sea still set up the valley of the 

 St. Lawrence to the head of the present hydrographical basin of Lake 

 Ontario. 



At the end of the Silurian Age the whole Upper Peninsula had emerged, 

 but the Lower Peninsula was still sea bottom. On the west the continent 

 reached down to Chicago, and, on the opposite side, its shore trended south- 

 east to London and the Niagara river. At the close of Devonian Time, the 

 Lower Peninsula marked the positiun of a vast bay opening southward. It is 

 not certain whether the anticlinals on the south of the Peninsula had an exist- 

 tence at this early period or not. It is more probable that the coal making 

 marshes of Michigan were continuous with those of Ohio, Indiana and Illi- 

 nois, but this is far from certain. 



At the end of the Carboniferous Age all Michigan was dry land. But 

 none of the great lakes existed except Superior. The region which is now 

 the centre of the Lower Peninsula was probably less elevated than the regions 

 which now lie upon the borders and in the beds of Lakes Huron and Michi- 

 gan. The surface denudations going forward through Mesozoic and Caeno- 

 zoic Time isolated the coal regions of Michigan and Ohio, if they were ever 

 connected, depressed the regions which were to become the basins of Lakes 

 Michigan, Huron and Erie, and excavated the first Niagara gorge. The 

 drainage of the great northern sea changed it to a lake of fresh water, in 

 which rose the St. Lawrence, flowing into the Atlantic, and probably another 

 great stream flowing through the hydrographical basin now occupied by Lake 

 Michigan and the Illinois river to the Mississippi and the Gulf of Mexico. No 

 traces of the Flora and Fauna of Michigan, during this long period, have 

 been preserved ; but without doubt, forms of animal and vegetable life adapt- 

 ed to the physical situation were abundant. 



At length the region which was to become Michigan was buried, in com- 

 mon with the entire northern part of the continent, beneath a burden of 

 accumulated snow and ice. This, like modern glaciers, underwent a slow 

 motion which imparted a grinding action to the sheets of ice, and materially 

 modified the surface features of the underlying country. The direction of 



