420 A. C. LANE 



top of the Sunbury in wells where the Berea Grit itself is absent. 

 In the extreme western part of the state, as at Dowagiac and Con- 

 stantine^ (one well only) less than 20 feet of red shale has to do duty 

 for Bedford to Sunbury, and the Antrim beneath is thin. I think 

 the red shale is the weathered top of the lower formation. It is 

 conceivable that the Berea Grit once extended farther and has been 

 eroded away. On the whole, however, it seems more likely that while 

 the whole period Bedford to Sunbury was one of elevation, there 

 were two times when the shore-line advanced farthest east — one just 

 before the Berea Grit, one just after the Sunbury shale, correlative 

 to the Buena Vista flags. 



There has been a question as to whether it would be better to 

 cut the Berea or Sunbury shale off from the Coldwater. But it was 

 included in the original definition of Coldwater and has been recog- 

 nized in Michigan only lithologically. It would seem best for the 

 present to keep the term Coldwater as originally introduced to cover 

 the interval from Berea Grit to Marshall, and use the Ohio terms 

 Sunbury and Cuyahoga, Buena Vista and Raccoon for fitting sub- 

 divisions when possible. 



Brines and sandstones seem to appear not really at the Berea 

 Grit level but somewhat above, but correlations are largely guess 

 work, as all of these sandstones are readily overlooked by drillers on 

 the one hand, and none of them are thick, and sandy, salty streaks 

 are liable to occur at various levels without question. Hard streaks 

 are also liable to occur which are largely bands of iron carbonate, or 

 they may be huge round kidneys, such as are known to exist. 



The outcrops of the Coldwater were described by the first Geologi- 

 cal Survey, Hubbard, and others, by Winchell in a long series of 

 papers,^ and by Rominger,^ who calls it and the Marshall, the Waverly 

 Group. It covers a considerable area. 



On the western side of the state the Upper Coldwater (or possibly 

 the Lower Marshall) about 300 feet below the top or 700 feet above 

 the bottom becomes distinctly more of a limestone. At least that 

 is one way to interpret the records. 



1 Annual Report for 1903, 281, 282. 



2 Biennial Report, i860. See also Weeks in Bull, igi on Marshall. 



3 Vol. Ill, Part I, chap, viii, 67, 75. 



