128 NEW YORK STATE MUSEUM 



to geographic causes. Nevertheless, the general parallelism of the 

 series of larger zones remains a fact of great importance for both 

 stratigraphic correlation and paleogeographic investigation. 



Another problem, always prominent in discussions of graptolite 

 horizons, is that of their correlation with the normal series of littoral 

 beds. In Scandinavia this problem is solved to a large degree by the 

 partial interlocking of the two facies. No such help has thus far 

 been offered the investigators in our shale belt, so far as the Lower 

 Ordovician graptolite shales are concerned, which, besides are 

 involved in the complex folding and faulting of the region. Never- 

 theless, several clues for a correlation of these shales have been 

 obtained, which may be mentioned in this place. 



One of these is the finding of a specimen of C a 1 1 o g r a p t u s 

 s a 1 1 e r i Hall in the Tribes Hill limestone by Prof. H. F. Cleland 

 (see Ruedemann, op. cit., 1904, p. 585). The graptolite has its 

 principal development in bed 2 of the Deep Kill shale (zone of 

 Didymograptus extensus and Goniograptus thureaui), although it 

 extends above and below this bed. Its prevailing occurrence in bed 2 

 agrees well with the correlation of the Deep Kill shale with the Beek- 

 mantown in general, and that of the Tribes Hill with the lower 

 Beekmantown (division B) in particular. 



Another clue is furnished by the finding of a characteristic grap- 

 tolite of the Deep Kill fauna in the Bellefonte section of Pennsyl- 

 vania.^^ This form, Airograptus (Dictyonema) fur- 

 ciferum, occurs in beds 2 and 3 (zone of Didymograptus 

 nitidus and patulus) and the lower part of the zone of Didymo- 

 graptus bifidus, in the Deep Kill section. It is therefore found in 

 about the middle of the Deep Kill section. 



In Bulletin 189, the species has been placed near the top of the 

 Nittany or the base of the Axeman, while Bassler, in the Biblio- 

 graphic Index, since published, refers the graptolite to the Stone- 

 henge or the basal division of the Bellefonte Beekmantown section. 

 Doctor Ulrich, in a letter dated April 22d, informs me that the 

 latter is the true position of the species, and that this fact agrees 

 with the view, at which he arrived years ago, namely, that the 

 Schaghticoke and Deep Kill graptolite shales hold a position below 

 the middle of the Beekmantown. This view is principally based on 

 evidence obtained in Arkansas. " There," Doctor Ulrich writes, 

 " the Phyllograptus occurs in the Jefferson city dolomite. Above 

 its zone, with an unconformity intervening, comes a zone with the 



" R. Ruedemann. Paleontologic Contributions from the New York State 

 Museum. N. Y. State Mus. Bui. 189, p. 20, 1916. 



