18(30.] ' ^ [Wiuchell. 



the Carboniferous Conglomerate and the summit of the arenaceous series 

 which has been locally designated Waverly, Marshall, Kinderhook, &c. 

 The Carboniferous limestone of Michigan has been shown '"^ on paleonto- 

 logical grounds to possess affinities with the median stages of the Carbon- 

 iferous Limestone series of the Mississippi valley. The Michigan Salt 

 Group has at length yielded some beds of fossiliferous flags, from which, 

 as might have been anticipated, it is shown to stand in close relation with 

 the same series. The Knobstones of Indiana and Kentucky, always 

 ranged by geologists within the limits of the Carboniferous system, pos- 

 sesses strong lithological affinities with the Waverly series, and withal 

 occupy the same relative position between recognized Carboniferous lime- 

 stones and the Black Shale. But paleontological evidence compels us to 

 elevate them into the zone of the Mountain Limestone which, at every 

 point of contact, is shown to lie above the Ohio psammitic series. Indeed, 

 it appears from observations made by others and by myself, that the Knob- 

 stone formation of Indiana and Kentucky, with the associated shales and 

 limestones, is substantially restricted to the horizon of the Keoku.k 

 division of the Mississippi Limestone series, or "Mississippi group. "'o^ 



The Silicious group of Tennessee is only a southward prolongation of 

 the same under changed peti'ogenetic conditions ; though in that State, the 

 silicious characteristics also invade the horizon of the Warsaw and St. 

 Louis Limestones — as may be seen along the valley of the Calf killer river, 

 and on the first bench of the ascent to the Cumberland Table Land. 



We come now to the series of strata, the determinations of whose 

 equivalencies has presented the most serious difficulties. The Gritstones 

 and Waverly sandstones of Ohio offer marked petrographic affinities with 

 the arenaceous strata of the Chemung and Portage groups of New York ; 

 and it is doubtful whether on purely lithological and structural grounds 

 we should ever be able to distinguish them. The same may be said how- 

 ever, and has been said, of the Knobstones of Indiana ; and the same is 

 also measurably true of a comparison between the Chemung and Catskill 

 strata, or the Catskill and Millstone Grit, or the Waverly and Millstone 

 Gi"it. There seems to be, moreover, a connection of contimaty between 

 the psammites of Ohio and the Chemung flags of Chatauque county. A 

 similar petrographic resemblance is apparent between the Marshall rocks 

 of Michigan in the northern and southern outcrops, and the Waverly of 

 Ohio. Furthermore, no little resemblance can be traced between these 

 sandstones and the yellow sandstones beneath the Carboniferous limestone 

 of Iowa. The Eockford limestone and the calcareous strata of the same 

 zone in Illinois and Missouri present considerable contrast, but they ap- 

 proximate, on the other hand, certain calcareous beds in the Waverly 

 series of Summit county, Ohio, and the Marshall series of Calhoun county, 

 Michigan. Moreover, these calcareous strata are intimately associated in 

 Illinois and Missouri, with arenaceous strata which everywhere recall the 

 aspect of the arenaceous strata of other States. In respect to stratigraphi- 

 es Mich. Geol. Kep. 1861, p. 103. 



los I propose the use of this term as a geographical designation for the Carboniferous Limestones 

 of the United States which are so largely developed in the valley of the Mississippi river. 



