THE GEOLOGICAL SECTION OF MICHIGAN 423 



A simple and natural explanation of faunal relations would be 

 that the Marshall emergence took place earlier to the southwest than 

 to the northeast. This does not agree with Schuchert's maps. If 

 so, the question at once arises, must we not reverse our definition 

 of the Lower Marshall, bringing it down to include the Raccoon 

 shales and their equivalent in Huron County, down to Port Hope 

 nearly, adding 200 feet to the Huron County section, and making the 

 Marshall there over 760 feet thick ? This may be the future solu- 

 tion of the question. Cooper leans to it. But we should be as sure 

 as possible before making changes. So we must ask what indications 

 are there of a land mass in this direction ? Also are there any indica- 

 tions of a shortened geological column to the top of the Marshall in 

 this direction ? 



There is a little thinning as compared with the Huron County 

 section, but not enough, and no shrinkage as compared with the 

 center of the basin. We have besides to allow for a dropping- 

 out of Berea beds and for the unusual thickness of the Huron 

 County Upper Marshall as given in the column which seems very 

 local. 



The limestone character of the western Coldwater is rather against 

 its earlier emergence, as well as the relatively wide spread of the 

 western Kinderhook. 



There is an alternative hypothesis (supposing the paleontological 

 facts to remain established) and that is to suppose that the Paleo- 

 neilo fauna of the Raccoon shales were immigrants northward that 

 reached Ohio earlier but did not reach Michigan until later — until 

 after the beginning of the Marshall. This seems to me the more likely 

 because the fauna most like that of the southern Michigan Marshall 

 that we find in Huron County is way up in the Lower Marshall at 

 Flat Rock Point. 



31. Michigan series, Lower Grand Rapids. Logan possibly 

 absent in Ohio? (380 — generally about 200). — The Marshall is 

 Kinderhook of the Illinois reports. Following the Marshall there was 

 an emergence and an interval of erosion without deposition of some 

 time around the edges of the basin, but perhaps none near the center, 

 for the series there is of greater thickness and its deposits of gypsum 

 attest its cut-off character. In the Mount Pleasant well it is 358 feet 



