Williams — Age of Manganese beds of Arkansas. 327 



of distinct eosilurian age (about equivalent to the Waldron 

 fauna of Indiana and the Clinton-Niagara fauna of New 

 York). This formation has been heretofore confused with the 

 St. Clair limestone of Penrose, but as it is of different geologi- 

 cal age it may appropriately receive a distinct name. I pro- 

 pose for it the name Cason limestone, in recognition of the 

 fact that the two limestones may be clearly distinguished on 

 the Cason tract as described in the Manganese Report of Dr. 

 Penrose.* 



The samples of ore from the Cason mine are in a calcareous 

 shale immediately underlying the Cason limestone and are of 

 special interest because of the evidence that the deposit is in 

 its original position and condition. Not only is there no indi- 

 cation of decay of the rock but the concretions found in the 

 rock are flattened and their long axes now lie in the plane 

 of the stratification. In the section of the O'Flinn mine the 

 ore appears also to be in its original position between the two 

 limestones. 



The following figure will illustrate the facts as they are here 

 explained and the way in which they contrast with the inter- 

 pretation given in the Manganese Report of Dr. Penrose. 



Bft.> Boone chert. 



Sylarnore sandstone. 

 Eureka shale. 



Cason limestone. ~) 



/Sfc.C. St. Clair limestone. ' St. Clair limestone 

 of Penrose. 



y 



Cason shale. 



Izard limestone. 



J 



The Izard limestone (A) is probably correct as it stands in the 

 Reports. Over the Izard limestone lies the St. Clair limestone. 

 As described in the Annual Reports up to 1890, the St. Clair 

 limestone includes all the strata between the Izard below, and 

 the Boone chert of the east, or, further westward, the Syla- 

 more sandstone, or, in the western part of the State the 

 Eureka shale, above. 



According to the interpretation required by the fossil faunas 

 this "St. Clair limestone" must be separated into three forma- 

 tions. The lowest division (B) is that part of the St. Clair 

 limestone of the Reports lying below the manganese horizon. 



* Ann. Rept. Ark., 1890, vol. i, Manganese, p. 124, etc. 



