Winchell.] ^^ [March 5, 



parallelize the rocks witli those of sui'roundmg States. '^ The followmg is 

 Mr. Hubbard's tabular statement of the succession of groups embraced in 

 the lower peninsula, 



A. Erratic Block group or Diluviums, 



B. Tertiary Clays, 



C. Coal measures, 



D. Sub-carboniferous Sandstones, 



E. Clay and Kidney Iron formation, 



F. Sandstones of Pt aux Barques, 



G. Argillaceous slates and flags of Lake Huron, 

 H. Soft, light-colored Sandstones, 



I. Black, aluminous slate, 



K. Lime rocks of Lake Erie.'* 

 In this table, as we now know, the groups marked D, F, and H, are but 

 different outcrops of the Marshall group ; and those marked E, G, and I, 

 but different outcrops of the Kidney Iron or Huron group. Following 

 Dr. Houghton in the report of 1838, Mr. Hubbard regarded the Pt aux 

 Barques sandstones and conglomerates as occupying a position beneath the 

 Kidney Iron formation of the southern portion of the state, and conse- 

 quently failed to identify the underlying shales. In the next place, Mr. 

 Hubbard identified with the Pt aux Bdrques shales, the shales of the 

 ' ' Michigan Salt group, ' ' struck in the salt wells at Grand Rapids, although 

 these latter actually occupy a position above the Marshall sandstones. 

 When, therefore, these sandstones and the underlying Huron shales were 

 struck in the boring of the salt wells, they were supposed to constitute 

 the third couplet of similar strata, and are set down as groups H and I, 

 in the above table.'* This confusion is illustrated by the following dia- 

 gram : 



Michigan Salt Group, ______^^ ^ — — — ^^^^ -^ 



Marshall Group, -=^ .'^■'•^ ^ ~^ G 



Huron Group, .. .s ss=^-—''~^ j 



The Pt aux Barques sandstone were rightly recognized by Hubbard as 

 the equivalent of the characteristic poi'tion of the Waverly sandstone se- 

 ries in Ohio ; and it is singular that they were not observed to be equally 

 identifiable with the sandstones of Hillsdale county in the southern part 

 of the state. The upper conglomeratic portion of the Pt aux Barques 

 sandstones was erroneously synchronized with the Carboniferous con- 

 glomerate, which though reposing on the Waverly of Ohio, is separated 

 from the equivalent Marshall in Michigan, by the Carboniferous limestone 

 and the Michigan Salt group. The Black Shale was also recognized as 



12 In his attempt, in 18-13, to parallelize the strata of Michigan with those of other states, Prof. 

 Hall assigned the Pt aux Barques series to the zone of the Waverly Series and the Portage and 

 Chemung; but he seems not to have known how to dispose of the roclcs denominated hy Hough. 



■ ton and Hubbard the "Upper Sandstone of the Peninsula." Rep. Geol., 4th Dist. N. .T., p. 619. 



13 See also Report, p. 136. '* Report, p. 133. 



