MEDINAN, NIAGARAN, AND CHESTER FOSSILS 
41 
regarded as merely the upper part of the Brassfield formation 
in this area. A chemical analysis of this so-called marl was 
published in the series of articles on the Clinton Group of Ohio,^ 
the term Clinton at that time being in use for the strata now 
known as the Brassfield. 
In the Hillsboro area, in Highland county, Ohio, the Silurian 
section consists of the following strata, named in descending- 
order. 
Guelph dolomite 
Lilley formation 
Bisher formation 
Alger clay shale 
Dayton limestone 
Brassfield limestone 
Belfast formation 
The term Guelph is used here merely to avoid using the term 
Cedarville dolomite for strata not containing a fauna similar 
to that of the Cedarville area. It does, however, contain Mega- 
lomus canadensis, species of Trimerella, and other fossils known 
in the Guelph of Ontario. Liospira perlata and tall species of 
Coelocaulus occur. 
The base of this so-called Guelph in the quarries in the eastern 
part of the town of Hillsboro is formed by a Pentamerus horizon 
which corresponds approximately to the Springfield dolomite 
of Greene, Clarke, Miami, Montgomery, and Preble counties, 
farther north in Ohio. The overlying part of this so-called 
Guelph should correspond in age to the Cedarville dolomite of 
the counties just mentioned, but it does not contain the same 
fauna. 
The Lilley formation includes that part of the section erro- 
neously identified many years ago by Prof. Edward Orton, as 
the Springfield stone. ^ This identification was based on the 
lithological appearance of the rock, it forming a promising 
’ Foerste, A. F,, The Clinton Group of Ohio; — Part IV: Denison Univ. Bull. 
Sci. Lab., vol. 3, pp. 3-12, 1888. 
* Orton, Edward, The Geology of Highland County; Geol. Surv. Ohio, Rep. 
Progress in 1870. Published in 1871, pp. 274-277. 
