The Description and Stratigraphic Relationships 

 OF Fossil Plants From the Lower Pennsyl- 

 VANIAN Rocks of Indiana. 



T. F. Jackson 



The outcrop of the Lower Pennsylvanian rocks in Indiana extends in a 

 belt of varying width in an east-of-south direction from Warren County on 

 the north to the Ohio river in Perry and Crawford counties on the south. 

 The outcrop in a few places is almost twenty miles in width although the usual 

 width is very much less. For the most part the rocks of this area are made 

 up of a series that vary greatly in lithologic characteristics both horizontally 

 and vertically. In places the formation consists of a massive sandstone ranging 

 in texture from rather coarse conglomerate to the fine-grained Hindostan 

 whetrock of Orange county. In other localities interbedded sandstones 

 and shales make up the formation. Locally coal beds occur and in a few 

 places iron ore is found at or near the base of the series. The series lies un- 

 conformably on Mississippian limestone, shale or sandstone. The great 

 similarity of the Upper Mississipian (Chester) shales and sandstones to the 

 shales and sandstones of the Lower Pennsylvanian has made the separation 

 of those two systems a difficult matter, especially when stratigraphic evidence 

 alone has been employed. This series of rocks is overlain by the shales, 

 sandstones or limestones of the Allegheny formation. Ashley' considered 

 that the boundary between the Pottsville and Allegheny series in Parke 

 county is found to come between the two Minshall coals, apparently about 

 the top of the limestones between the two coals. 



The series of rocks briefly described in the foregoing paragraph is the 

 "Millstone grit" of the early geologists and the "Conglomerate" and "Con- 

 glomerate sandstones" referred to in the earlier State Reports. Hopkins 

 in his report on "The Carboniferous Sandstones of Western Indiana,"- pro- 

 posed the term "Mansfield Sandstone" for the series. Later Ashley placed 

 the series in what he designated "Division I." He retained the term "Mans- 

 field sandstone" for the massive bed or beds of sandstone that occur locally 

 in the series.^ As the fossils obtained from these rocks show that the rocks 

 are of the Pottsville age there is no good reason why that name should not 

 be applied as suggested by Ashley.* 



The Pennsylvanian rocks that occur within the area included in the Bloom- 

 ington Quadrangle represent in part the Pottsville or Ashley's "Division 



1 33rd An. Rep. Ind. Dept. Geol. and Nat. Res. p. 58, 1908. 



2 20th An. Rep. Ind. Dep. Geol. and Nat. Re.s. 1895. 



3 23rd An. Rep. Ind. Dep. Geol. and Nat. Res. p. 95, 1896. 

 1 33rd An. Rep. Ind. Dep. Geol. and Nat. Res. p. 58, 1908. 



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