660 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



feet of pure Stonehenge limestone consists of dolomite. The Mercersburg 

 section, therefore, not only compares much better lithologically with 

 the Belief onte section than does the one of Chambersburg, but also affords 

 a reasonable basis for the identification of the Stonehenge in the Nittany 

 Valley. 



Toward the southwest from Bellefonte the Stonehenge, and at least 

 a large part, if not the whole, of the ISTittany dolomite wedges out, so 

 that just north of Martinsburg, Pennsylvania, the Axeman limestone, 

 which is there easily recognized by its fossils and lithology, comes well 

 down toward the Ozarkian boundary. The Nittany dolomite, besides 

 being thinner, is also more cherty than at Bellefonte, so that care is 

 required in discriminating it from the cherts of a middle Ozarkian for- 

 mation — carrying Gasconade fossils near its top — with which it comes 

 into contact south and southeast of Eoaring Spring. Fortunately, the 

 most commonly fossiliferous of the Nittany chert zones is near the base 

 of the formation and is marked by so characteristic a fossil as Ophileta 

 complanata. 



Still another cherty zone has been found apparently above the Axeman 

 limestone a few miles north of Martinsburg. This contains Maclurea cf. 

 speciosa, large opercula of the type for which I have proposed the name 

 ^'Ceratopea''' (see page 665), Trochonema sp., and a Urate Helicotoma, 

 or perhaps Gyronema, a faunule suggesting the Yellville in Arkansas 

 and more remotely the horizon between the middle of "Division D" and 

 the base of "Division E" in the Champlain section. If the position 

 of this chert is correctly determined, it must belong to the Bellefonte 

 dolomite, in which case the fossils would be a welcome addition to the 

 scant fauna of this formation. However, it is quite possible that the 

 zone belongs beneath the Axeman, hence in the upper part of the Nittany. 



Detailed correlations between the Canadian rocks of central Penn- 

 sylvania and those of the Champlain Valley in New York and Canada 

 seem impossible at this time. Large collections of fossils from both 

 regions are in hand, but the material requires preparation and more 

 careful study than has yet been given it. At present the general trend 

 of the faunal evidence only has been determined, and while this justifies 

 the statement that the Canadian limestones and dolomites of the two 

 areas are in essential accord, it is yet too early to attempt correlating 

 the successive zones. The suspicion engendered by the present aspect 

 of the problems that a considerable hiatus, only partially filled by reef de- 

 posits at Fort Cassin, occurs between D and E in the Champlain section, 

 is perhaps the chief reason why a delay as to details is desirable. Pend- 



