REPORT OF THE DIRECTOR I919 II9 



of its true age, although the Hthologic identity of the rocks (green 

 and black shale with thin limestone intercalations) with that of the 

 Deep Kill shale gives these beds the appearance of introducing a new 

 age rather than closing an old one. Meanwhile, however, it has been 

 recognized in Europe, especially through Moberg's work, from the 

 accompanying biota that the Dictyonema shale introduces an exten- 

 sive Ordovician transgression and therefore is properly considered 

 as the basal horizon of that period. 



Suhhorizons 



It was already suggested in Bulletin 69 that the Schaghticoke beds 

 may comprise two subhorizons, for there were found, on one hand, 

 the shale filled with Dictyonema flabelliforme on the 

 brow of the cliff forming the south bank of the Hoosic river bed ; 

 and, on the other, the shale with Staurograptus dichoto- 

 m u s Emmons (= Clonograptus proximatus Matthew) 

 in the river bed itself. The latter shale contains a few specimens 

 of Dictyonema flabelliforme acadicum Matthew 

 which bring the subzone under the general division of the Dic- 

 tyonema flabelliforme zone. On account of the contorted condition 

 of the rocks, which did not allow a clear decision as to which horizon 

 was the- upper one, we refrained at the time from separating the two 

 horizons. Since, however, in Europe the corresponding horizons, 

 namely, that of Dictyonema flabelliforme forma typica, and that of 

 Clonograptus tenellus, are already distinguished, and further it being 

 obvious that Staurograptus dichotomus is a closely 

 related, vicarious 'form of. C' 1 o n o' g r a p t u; s t e n. e/ 1 1 u & , it 

 is preferable to separate the two horizons, for there can be hardly 

 any doubt that the Staurograptus horizon is above that of Dictyonema 

 flabelliforme. Westergard^^ even interpolates still a third zone, 

 that of Clonograptus tenellus and Bryograptus hunnebergensis 

 between the zone of Dictyonema flabelliforme and that of Bryo- 

 graptus kjerulfi, Clonograptus tenellus and Dictyonema norvegicum. 

 Hahn^'' came to a similar division of the zone from his exhaustive 

 study of the Dictyonema fauna of Navy Island at St John, N. B. 

 He was able to distinguish a fauna of Dictyonema fla- 

 belliforme acadica and conferta, associated with 

 Staurograptus and another, younger one, of D i c t y o - 



"A. H. Westergard, Studier ofver Dictyograptusskiffern etc., Meddelande 

 fran Lunds Geol. Faltklubb, ser. B, no. 4, 1909. 



" F. F. Hahn. On the Dictyonema-fauna of Navy Island, New Brunswick, 

 Ann. N. Y. Acad. Sci., 32: 153. 1912. 



