Michigan Gypsutn Deposits- — Grimslcy. 381 
GEOLOGICAL HISTORY OF THE MICHIGAN BASIN. 
At the opening of the Carboniferous period, Lower Michi- 
gan, Ohio, and a large part of Pennsylvania, were covered by 
a gulf which opened to the northwest across Illinois and Min- 
nesota. In the earlier part of the Mississippian epoch, the land 
was sinking around this gulf, especially to the south and south- 
west and in this sinking area were deposited the sediments of 
the Kinderhook stage, forming limestones, sandstones, and 
shales, mainly shallow water deposits irregular in extent, vary- 
ing in fossil contents, so that the same series of rocks has been 
given a variety of names by geologists. These names are often 
used in local geology, but now are known to be contemporan- 
eous, and they are included under the name of Kinderhook. 
By the close of this divison of time, the large gulf extended 
south into Arkansas and Tennessee and west to the Rocky 
mountains, and opened northwest across the Dakotas. 
For a long period of time the salt water gulf remained 
stable and quiet, supporting a rich fauna of corals and crinoids, 
which have formed the Burlington and KeoKvik limestones, 
known throughout the world on account of the variety and per- 
fection of their crinoid and brachiopod fossils. These lime- 
stones and other formations, related in time, have now been 
grouped under the name of Osage or Av.gusta. 
While there were many local and minor varrations in the 
physical conditions, and therefore in the life characters In 
this gulf, there was a greater and more important contrast in 
these characters between the eastern and western portions, sep- 
arated by the Cincinnati island. These have been named by 
Weller* the eastern or Waverly province, and the western or 
Osage province. 
In the Kinderhook gulf the faunas were intermingled to a 
very considerable extent ; but in the Osage age the clear waters 
of the Osage gulf supported a fauna which could not flourish in 
the sediment-laden waters of the Waverly province. 
The land to the northeast of this Carboniferous gulf was 
above sea level, the drainage system of that highland carried a 
large quantity of mud and sand sediment into the Waverly gulf, 
forming the conglomerates, sandstones, and shales of that area. 
"Journal of Geology, vol. vi, p. 308. 
