WiQChelL] ^^ [Marcli5, 



In the several documents to wliicli I liave just referred, I stated distinctly 

 that I regarded the Marshall sandstones of Michigan as the equivalents of 

 the Fine grained sandstone series of Ohio, and the Black Shale of Michigan 

 as equivalent to the Black Shale of Ohio and Indiana. I also stated as a 

 matter of stratigraphical demonstration, that these black shales are seen in 

 Thunder bay of Lake Huron and in Grand Traverse bay of Lake Michigan 

 to rest above the well characterized Hamilton limestones. I had at first 

 considered these black shales as the equivalent of the Genesee Shale of 

 l^evf York,*3 but in deference to the judgment of Professor Hall, person- 

 ally expressed, I united them with my overlying Hudson group, which 

 was organized to receive a series of bluish and greenish argillaceous strata 

 beneath the Marshall sandstones, and supposed by me to correspond to the 

 Portage group of New York-^^ I was not aware at that time, that Mr. 

 Murray had had an almost identical experience, ^^ as I have already stated. 



In 1860, Professor Swallow^^ published descriptions of 19 species of fos- 

 sils from the Chouteau and Lithographic limestones of Missouri ; and in 

 the same year, Mr. Lyon^s published a section of the rocks of Kentucky, 

 in which he ranges the " Knobstone formation" under "sub-carbonifer- 

 ous," and inclines to place the Black Slate in the same position. 



Early in 1861, Professor HalP^ published "Notes and Observations 

 upon the Fossils of the Goniatite Limestone in the Marcellus Shale of the 

 Hamilton group in the eastern and central parts of the State of New York, 

 and those of the Goniatite beds of Eockford, Indiana, with some anala- 

 gous forms from the Hamilton group proper." In this paper Professor 

 Hall returns with strong assurance to his original opinion enunciated in 

 1842, that the Black Shale of the West is the equivalent of the IVfarcelhis 

 of New York, and that the ferruginous sandstones of Ohio and Indiana, 

 are the equivalents of the Portage and Chemung. He describes as new 

 18 species from the Eockford beds including those recognized as Goniatites 

 rotatorius,^= and Ooniatites -princeps^ij \ ernavA, and two species previously , 

 described by Meek and Worthen. He, however, fails to identify a single 

 species from the Eockford limestone with any species occurring in the 

 Marcellus Shale or other Devonian rocks of New York. 



The same number of Silliman's Journal which contained the announce- 

 ment of my official report, contained also a paper by Messrs. Meek and Wor- 

 then^s on the "Age of the Goniatite Limestone at Eockford, Indiana, and 

 its relations to the Black Slate^of the Western States, and to some of the 

 succeeding rocks above the latter." These authors deny that any portion 

 of the Black Slate is found above the Goniatite limestone, as had been 

 asserted by Christy, and announced that it lies entirely below. The 

 limestone they identify with the Chouteau limestone of Missouri, founding 

 the opinion on an identification of at least six out of 23 or 24 Eockford 

 species, and a close resemblance amongst most of the others. They argue 



49 Mich. Geol. Rep., 1861, p. 78. ™ lb. pp. 79 and 139- 



51 In alluding to' this fact in my report, I Inadvertently attributed this experience to Mr- Billings; 

 Report, p. 79. ' '•'''■ Trans. St. Louis Acad. Sci., 1, 035- 



S3 Trans. St. Louis Acad. Sci.. 1, 620. " xiii. Report New York Regents App., p. 95. 



« This is described as U. Ixion, in a note, p. 125. ''" Amor. Jour. Sci.. [2] xxxiii., 167. 



