12 



itself toward the south, and until the ancient Laurentian 

 outlet was re-established, the overflow of the lake region was 

 to the south into the Ohio and Mississippi valleys. 



The channels of the great ancient water-ways can still 

 be traced and are very clearly shown upon the accompanying- 

 relief map of the region. (PI. II.) 



One of them extended from the present western end of 

 Lake Erie, southwesterly through what is now known as the 

 valleys of the Maumee and Wabash rivers and emptied into 

 Ohio river. The other connected the lower extremity of Lake 

 Michigan with the Mississippi river along the present valleys 

 of the DesPlaines and Illinois rivers. 



At first these glacial lakes were entirely separated by the 

 high land in the interior of the state, the ice forming a 

 barrier to any communication on the north, and as the land 

 to the south and west of Lake Michigan was lower than that 

 lying south of Lake Erie, their waters were not on the same 

 level. The beach of Lake Maumee — as it is called — 

 being about 237 feet above the present level of Lake Erie, 

 while the beach of the western lake, or Lake Chicago, was 

 only about 125 feet above that of Lake Michigan. 



As soon, however, as the ice had retreated far enough 

 north to expose the valley of an ancient pre-glacier river, 

 sometimes called the Huronian river and which is now known 

 as the Saginaw-Grand valley, extending across the state from 

 Saginaw Bay to the mouth of the Grand river, a channel was 

 made which connected the two lakes. This resulted in the 

 lowering of the water of Lake Maumee to the level of Lake 

 Chicago, and the consequent closing of the Maumee outlet, 

 and from that time until the St. Lawrence was reopened, the 

 only outlet of the eastern lake was through this channel 

 into the western lake and from that through the DesPlaines 

 outlet into the Mississippi. 



This channel across the state, as shown by the map, 

 (PI. Ill) was, in nearly all its course, several miles in width, 

 and was from forty to one hundred feet in depth, and in the 

 narrow portions there was doubtless a strong and very rapid 

 current. 



The remnant of this channel is to-da} r the most conspic- 

 uous feature in the topograph}' of the state. It is well shown 

 upon the relief map. At the present time the highest land 

 in this valley between Lake Michigan and Lake Huron is 

 only a little more than seventy feet, and it is said that in an 

 early day in Gratiot county, where the head waters of the 

 existing rivers centre, in the times of high water in the spring 



