406 R. M. Field — Middle Ordovician of Central 



sections, though, several of the sections in the present 

 paper are not mentioned in them. 



In brief summation, then, of the work on the Middle 

 Ordovician limestones of central and south-central Penn- 

 sylvania during the state surveys, it may be truthfully 

 said that Rogers gave a remarkably full and accurate 

 description of the faunas, for his time, but that the 

 Second Survey added very little to what was already 

 known. Hall and Simpson were the chief cataloguers of 

 fossils during this period, but even they did little or 

 nothing to elucidate the Ordovician faunas of central 

 Pennsylvania. To Simpson, however, must be given the 

 credit for the discovery and description of the new and 

 curious trilobite Homalonotus (Brongiartielli) trenton- 

 ensis. 



In 1903, Collie (5), in his paper on the Belief onte sec- 

 tion, gave the first detailed and correlative description 

 of the Middle Ordovician limestones and faunas, in part 

 as follows : 



"There is apparently no true Chazy present, but rocks con- 

 taining the fauna of the Stones River Group, which includes the 

 Birdseye zone of New York as its upper member, follow imme- 

 diately on the Beekmantown. These in turn are followed by the 

 Black River and Trenton Groups, above which follow in order 

 the Utica and Lorraine shales. ' ' 



Collie gives a detailed description of the Trenton, which 

 he divides into eight fossiliferous zones, but he does not 

 appear to appreciate the difference in fauna and lithol- 

 ogy between the lower and upper limestones. His f aunal 

 list for the Trenton of the Bellefonte section is, as a 

 whole, remarkably complete and the writer has been able 

 to add only a few species, but his list of the Stones River 

 species is incomplete, as he failed to report many of the 

 thoroughly critical and distinctive types contained in this 

 formation. 



The following year Grabau (6) commented upon Col- 

 lie 's upper Beekmantown as follows : 



' ' Since the fossiliferous horizon below the 2335 feet of unf os- 

 siferous (? ) beds is upper Beekmantown and the first fossili- 

 ferous horizon is Upper Stones River (Upper Chazy), the lower 

 Stones River, or Chazy proper, seems to be represented by this 

 unf ossilif erous ( % ) horizon. If, then, this series is taken from 

 the Beekmantown and added to the Chazy, we have 2500 feet 

 (±) of the latter, a division which agrees more fully with the 



