96 Bulletin 12 224 



was referred to in this correlation, but it was probably the River- 

 side. 



In 1870 Prof. Winchell published a paper on the "Geological 

 Age and Equivalents of the Marshall Group."* A catalogue of 

 the fossils of the Marshall group and its supposed equivalents in 

 the United States is given. From, this catalogue it appears that 

 there are nine species common to the Rockford limestone and the 

 Marshall group. The Rockford limestone and a sandstone in 

 northern Indiana, which in the table of geological equivalents is 

 called the Williamsport sandstone, are correlated with the Mar- 

 shall group. The exadl stratigraphic position of the Williams- 

 port sandstone is not shown and no satisfactory reasons are given 

 for considering it the equivalent of the Rockford limestone. 

 The presence in the Marshall group of such a charadteristic 

 Rockford species as Goniatites oweni affords strong evidence that 

 the Rockford limestone is the equivalent of some part of the Mar- 

 shall group, but that the three hundred feetf of sandstones and 

 shales constituting Winchell's Marshall group in Michigan should 

 be represented by only three or four feet of limestone in southern 

 Indiana is not probable. 



The Report of the State Geologist of Indiana for 1873 contains 

 the following sedlion of the rocks in the southern part of the 

 state by W. W. Borden J: 



Feet. 



Soil and clay 20-40 



Knob limestone — Keokuk group 80 



Knob sandstone. 

 Knob shale. 



[ Kinderhook group 344 



New Albany Black slate. 



Crinoidal limestone. \ Hamilton group 140 



Hydraulic limestone. 



*Proc. Am. Phil. Soc, 12, pp. 385-418. 

 fProc. Am. Phil. Soc, vol. 11, p. 74. 

 tP. 172. 



