246 Frof. H. Alley ne Nicholson — 



to definitely establish, the precise position of certain of the Grapto- 

 litic zones of Britain, the exact geological place of which has 

 hitherto been a matter of some dubiety. This is especially the case 

 with the •' Upper Graptolitic Schists " of Sweden, which unmis- 

 takably correspond with the " Coniston Mudstones " of the North of 

 England. It is highly satisfactory to me to know that Dr. Linnars- 

 son's investigations fully corroborate the view always maintained 

 by Prof. Harkness and myself on this matter — namely, that the 

 " Coniston Mudstones " are indubitably inferior to the true Upper 

 Silurian Kocks. 



From a study of Dr. Linnarsson's paper, it will be seen that the 

 following five Graptolitic zones are recognizable in Sweden and 

 iS^orway : 



1. Olenus Schists and Dictyonema Schists, wit hi Didyonema 

 flahelliformis, Eichw., and Bicliograptiis tenellus, Linnarsson. The 

 latter is not a true Dichograjptus, but belongs, together with the form 

 which I described from the Upper Skiddaw Slates under the name of 

 Dichograptus gracilis^ to a new genus, which I propose to name 

 Trichograjotus. The Olenus Schists and Dictyonema Schists of 

 Sweden may be paralleled, with great probability, with the " Trema- 

 doc Slates " of Wales ; and as far as the Graptolites are concerned, 

 may be regarded as a single group. 



2. Lower Graptolitic Schists. — These beds contain species of 

 Fhyllograptus, Tetragraptus, and Didymograptus, and are the un- 

 doubted equivalent of the Skiddaw Slates of the North of England 

 and the Quebec group of Canada. This is an interesting point, as 

 the Swedish beds rest upon strata containing unequivocal Lower 

 Silurian fossils ; whereas the age of the Skiddaw and Quebec 

 deposits has always been a matter of some uncertainty. 



3. Middle Graptolitic Schists. — These are beyond question 

 the equivalent of the inferior portion of the Moffat series of the 

 South of Scotland (the ''Lower Moffat Shales" of Mr. Charles 

 Lapworth). They are characterized by the occurrence of Climaco- 

 graptus ter^tiusculus, His., and species of Dicellograptus and Dicrano- 

 graptus, together with the total absence of species of Monograptus 

 and Bastrites. 



4. Upper Graptolitic Schists. — The lower portion of these is 

 equally beyond doubt the precise equivalent of the ''Coniston 

 Mudstones " or " Skelgill Series " of the North of England (and of 

 the "Upper Moffat Shales" of the South of Scotland). They are 

 characterized by the absence of Didymograptus and Dicranograptus, 

 and the presence of species of Monograptus, Bastrites, Diplograpttis, 

 and Clirnacograptus. Beds of the same age, and containing the same 

 species of Graptolites, have recently been recognized by Dr. Guido 

 Stache as occurring in Carinthia, and have by him been paralleled 

 with the Coniston Mudstones (Die Graptolithen-Schiefer am Ostering- 

 Berge in Kiirnten), 



5. Upper Silurian. — Though poorly represented in Sweden, a 

 fifth Graptolitic zone exists (well developed in Norway), which is of 

 Upper Silurian age, and is characterized by the occurrence of Mono- 



