Drainage of Carboniferous area, Michigan. — Mudge. 301 
by way of the Ottawa river, which is found to have drained 
the Huron, Michigan and Superior basins for about 24,000 
3 T ears. 
The highest of the beaches about the head of lake Michigan 
(at 45 feet) has been regarded as the equivalent of the Mau- 
mee beach, or not a lower strand, and therefore the oldest well 
defined beach of the region, although it is only a few feet 
above the present and recently deserted shores. 
Owing to the terrestrial deformation, the Ottawa outlet of 
the Huron basin was closed by the rim being raised so high as 
to turn the overflow into the Erie basin. This northeastward 
uplift also affected the outlet of the Erie basin, and on ac- 
count of the presence of the Johnson ridge, about a mile north 
of the present site of the falls of Niagara, caused an actual 
overflow of the drainage of all the upper lakes into the tribu- 
taries of the Mississippi. At that time the lacustrine silts 
upon the prairies at the head of lake Michigan were laid down. 
But the Niagara falls were receding at the rate of about four 
feet a year and completed the incision through the Johnson 
ridge about 1,500 j^ears ago,* thus overcoming the terrestrial 
uplift of the Niagara district (which is about a foot and a 
quarter a century), and then the level of lake Erie was lowered 
to about 17 feet below the Chicago divide. The slightly raised 
beaches about the head of lake Michigan mark this late sub- 
siding of the waters. The lowering of the waters by the 
recession of the falls has preserved the present outlet of the 
lakes for a further period, but if the late rate of terrestrial 
deformation shall continue in the future, the drainage of the 
upper lakes will lie diverted from the Niagara into the Missis- 
sippi in perhaps 5,000 or 6,0(»u years, so that this result will 
be reached before the falls shall have receded to Buffalo. 
DRAINAGE SYSTEMS OF THE CARBONIFEROUS 
AREA OF MICHIGAN. 
By E. H. MUDGE, Belding, Mich. 
The rock formations of Michigan commonly referred to the 
Carboniferous period, include the Subcarboniferoue limestone 
*"Deformation of the Luody lieach and Birth of Lake Erie," before 
cited. 
