EARLY EXPLORATIONS 49 



tioD, it seems advisible for tbe present to retain Meek and 

 Worthen's name for these rocks as exposed along- the line of 

 the Mississippi river. 



Among the earliest references to the rocks of this group 

 in the continental interior is that made in connection with 

 Owen's explorations in southeastern Iowa.* This author 

 called some sixty feet of ash-colored shales exposed above the 

 level of the water in the Mississippi river to the base of the 

 encrinital limestone at Burlington the "argillo-calcareous 

 group," and regarded it as belonging to the lower part of the 

 Subcarboniferous. These shales were actually a portion of the 

 median member of what Swallow f in Missouri had termed the 

 "Chemung" group. This group was divided into (1) the 

 Chouteau limestone, ( 2 ) the Vermicular sandstone and shales, 

 and ( 3 ) the Lithographic limestone. Within the limits of the 

 region under consideration the three divisions are quite per- 

 sistent and easily recognizable over wide areas. The last two 

 members have recently been termed, and very appropriately, 

 the Hannibal shales and the Louisiana limestone respectively, 

 since at the places in northeastern Missouri bearing these 

 names they are exposed in their full development. 



Throughout Iowa, Illinois and Missouri, at least, and per- 

 haps in other states also, wherever the Kinderhook rocks are 

 exposed, its members, as here designated, will always be recog- 

 nized to a greater or less extent as convenient stratigraphical 

 unit, particularly in faunal studies. Over all three of the 

 states named these subdivisions are sharply defined lithologi- 

 cally, except possibly toward the northern known limits, 

 though there the rocks have received comparatively little or 

 no attention. At the present time it seems very probable that 

 the third or lowest member — the Louisiana or Lithographic 

 limestone — will find a closer relationship with the Devonian 

 than with the Carboniferous, and that eventually it will be re- 

 garded as the capping stratum of the former over all the terri- 

 tory contiguous to the Mississippi. 



•Geol. Snr. Wisconsin, Iowa and Minnesota, p. 92. 1852. 

 t Ann. Kep. Geol. Sur. Missouri, p 103. 1855. 



