REPORT OF THE STATE PALEONTOLOGIST 1901 573 



beds, which form the lower part of the upper Skiddaw slates. 

 Didymograptus bifidus rises there into this zone, 

 while, on the other hand, P h y 1, lograptus anna and 

 Phyllograptus angustif olius are not reported by 

 Miss Elles from these beds. Marr, 1 however, also cites the lat- 

 ter species. As Dr Gurley has also found Did. bifidus 

 in the corresponding Point Levis zone and Phyllograptus 

 anna in association with these Diplograptidae in Arkansas, 

 it is apparent that these species rise in various regions into 

 this zone. 



The Ellergill beds are correlated by Lapworth, Marr and Elles 

 with the Llanvim beds of Wales; and by Miss Elles with Tull- 

 berg's zones ri), zone of Glossogr aptus and o), zone of D idy mo - 

 g r aptus g e minus , which form the basal part of the middle 

 graptolite shales or of the Dicellograptusskiffer of Scania. These 

 zones also contain the genera Diplogr aptus, Climacograptus, 

 Glossograptus and Cryptograptus. The latter zone has again 

 been subdivided into three subzones, the lowest of which 

 (y) still contains Didymograptus bifidus. This 

 would suggest that the presence of the above cited species of 

 the Phyllograptus anna zone in the zone with D i p - 

 lograptus dentatus in America may eventually allow 

 the recognition of subzones in the latter. 



It will be noticed that in England this zone is placed above 

 the Arenig formation, and that the corresponding zone in Scania 

 is united with the middle graptolite shales, that, hence, impor- 

 tant formational boundaries separate, in Europe, this and the 

 preceding zone. This fact, in connection with the decided change 

 in the character of the genera, which are those of the Middle 

 and Upper Champlainic or Lower Siluric, may with our advanc- 

 ing knowledge of the graptolite facies of the Champlainic lead 

 to the correlation of this zone with some part of tne Chazy 

 formation. This supposition seems to be well supported by a 

 statement of Mr Walcott (see Gurley, loc. cit. p. 304), that " in 

 Nevada Didymograptus bifidus occurs in strata cer- 

 tainly supra-Calciferous and probably of Chazy horizon.' 



'/•> 



1 Geol. mag. 1894. 14th ser. 1:127. 



