396 



REl'ORT OF STATE GEOLOGIST. 



It will be the purpose of this paper to indicate the stratigraphic 

 relationship of the Waldron shale to the other subdivisions of the 

 Silurian and to present the available data regarding the compo- 

 sition and distribution of its fauna. The relationship of the Wal- 

 dron fauna to the faunas of the Laurel and the Louisville limestones 

 which were respectively its predecessor and successor in this region 

 will also be considered. 



STRATIGRAPHY. 



The Silurian rocks of southern Indiana comprise three distinct 

 limestone formations, which are separated by two shale horizons. 

 The higher of the two argillaceous beds is called the Waldron 

 shale and separates the Laurel limestone from the Louisville lime- 

 stone, which is the highest division of the Silurian series in this 

 area. The general relationship of the several formations of the Si- 

 lurian in southern Indiana is expressed in the following table show- 

 ing their order of superposition : 



Louisville limestone. 

 Waldron shale. 

 Silurian <^ Niagaran group <J Laurel limestone. 



Osgood beds. 

 Clinton limestone. 



The so-called Clinton rests directly upon the Richmond forma- 

 tion, the uppermost beds of the Ordovician. The Guelph dolomite, 

 which terminates the Niagaran group in New York, is absent in 

 southern Indiana, the Devonian limestone resting unconformably 

 on the Louisville limestone. 



Dr. M. N. Elrod" first introduced the name Waldron shale for 

 the beds from which Prof. James Hall" had previously described the 

 rich fauna at Waldron. 



The Waldron shale is composed mainly of fine textured blue to 

 greenish clay shale. Thin bands of impure limestcme and calcareous 

 nodules sometimes occur in the shale but represent a comparatively 

 insignificant x)i'oportion of the formation. The Waldron shale has 

 a thickness ranging generally from four to ten feet. So far as ob- 

 served by the writers the Waldron beds are conformable with the 

 Niagara limestone beds above and below it. Elrod^ reports that 

 the shale is unconformable with the Laurel limestone at the Tarr 



"Geology of Docatur County, 12th Ann. Rcpt. Ind. Dept. Geol. and Nat. Hist., 

 1S82, pp. 109-111. 



'•28th Ropt. N. Y. State Mus., 1870. pp. 100-199. pis. 3-34. 



' NiiiKura ^roiip uik oiifoi init ics in Indiimn. Proc. Ind. Acad. Sci. 1901, p. 212. 



