198 Mr. C, Lapwortli on the Geological 



formity. Of the very lowest beds of the Upper Division we 

 as yet know little with certainty. The deepest zone recog- 

 nizable at the present time is the 



5. Zone of Coenograptus gracilis, Hall (or of Dicellograptus 

 sextans, //.). — This is typically developed in the lower portion 

 of the Glenkiln shales of the south of Scotland. It is the 

 first of the Dicellograptidian zones, and is well particularized 

 by the peculiar genus Coenograptus. Only a single Dicho- 

 graptid (D. superstes, Lapw.) survives. Dicranograptidas are 

 abundant, Dicranograptus ziczac, Lapw. , D. formosus, Hopk., 

 Dicellograptus sextans. Hall, D. intortus, Lapw., are peculiar, 

 and several Diplograpta, such as Hallograptus bimucronatus , 

 Nich., H. ? rnucronatus. Hall, Diplograptus Whitfeldi, H., &c. 

 This zone was first recognized by Hall in theNormans-Kill beds 

 of the valley of the Hudson. In Britain it occurs near Builth, 

 at Portmadoc; in Scandinavia in the Middle Graptolite schists 

 of Scania ; and, in all probability, also exists in the Ordovician 

 rocks of Australia. 



6. Zone of Dicranograptus Clingani, Carr. — This includes 

 the dark shales that are supposed to underlie the Bala Lime- 

 stone of North Wales, and finds its most perfect type in the 

 Lower Hartfell shales of the south of Scotland. Its peculiar 

 forms axe Dicranograptus Clingani, Qaxx.,DicellograptusForch- 

 ammeri, Geinitz, Lasiograptus Harknessi, Nich. It is Avell 

 developed at Conway, North Wales, at Moffat (Lower Hart- 

 fell) , at Girvan, in the north of Ireland, in Scania at many 

 localities, and in the lower beds of the Lorraine shales of 

 North America. 



7. Zone of Pleurograptus linearis, Carr. — This zone in all 

 probability includes the horizon of the Bala Limestone of 

 North Wales and of its equivalent the Chasmops Limestone 

 of South Sweden. It is remarkable in Scotland for the abun- 

 dance of Leptograptida} it affords, the genera Amphigraptus 

 and Pleurograptus being almost strictly confined to this zone. 

 Its peculiar Moffat forms are Leptograptus capillar is, Carr., 

 Amphigraptus divergens, Hall, Diplograptus quadrimucro- 

 natus, Hall, Climacograptus tubuliferus, Lapw., all of which, 

 with their Moffat associates, mark the same zone in Girvan, 

 in County Down, at Rostanga in Scania, and apparently also 

 in the Hudson-River group of North America. 



8. Zone of Dicellograptus complanatus, Lapw. — The strata 

 that lie between the zone of P. linearis, Carr., and the sum- 

 mit of the Ordovician system form in South Scotland two 

 very distinct zones, though few Rhabdophora have yet been 

 described from them. The lowest zone is that of Dicello- 

 graptus complanatus, Lapw., which contains but few peculiar 



