Swedish and British Graptolitic Deposits. 



245 



vertical distribution of the genera of Graptolites in the Cambrian 

 and Silurian rocks of Sweden : — 





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Dichograptus 









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s 





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jDictyonema 









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X 























Phyllograptus 















X 



X 

















Tetragraptus 















X 



















Didymograptus 















X 





X 















Dicellograptus 



















X 





X 











Bicranographis 



















X 















Climacograptus 























X 









X 







Diplograptus 



















X 



X 



X 





X 







Graptolithus 



























X 







Sastrites 



















V 









X 







RetioUtes 



























X 







II. — Notes on the Correlation of the Graptolitic Deposits 



OF Sweden with those of Britain. 



By H. Alleyne Nicholson, M.D., D.Sc, F.E.S.E. ; 



Professor of Natural History in the Uniyersity of St. Andrews. 



(PLATE IX.) 



THE foregoing paper was sent to me by Dr. Linnarsson, along 

 with a fine collection of Swedish Graptolites ; and I am happy 

 to be the medium through which his interesting observations appear 

 before the English public. With singular acumen, the distinguished 

 Swedish geologist has unravelled the intricacies which beset the study 

 of the distribution of the Graptolites in past time ; and his results 

 are of peculiar importance and value. Some of these results, in so 

 far as they especially bear upon British Geology, may just be in- 

 dicated here. 



In the first place. Dr. Linnarsson has shown (what British 

 palagontologists have long been trying to prove) that certain species 

 and genera of Graptolites are restricted to certain very definite 

 horizons. He has thus added fresh force to the opinion (which some 

 have regarded as exceedingly doubtful) that the Graptolites may be 

 safely relied upon as guides in stratigraphical arrangement — their 

 value in this respect being at least equal to that of the Trilobites. 

 Secondly, Dr. Linnarsson's researches afford another and a very 

 striking proof of the singularly uniform manner in which Grapto- 

 lites have been distributed throughout the world at corresponding- 

 periods of time — the same zones, with the same genera and species, 

 being certainly recognizable in all regions which have hitherto been 

 properly investigated. Thirdly, by means of the clear and satisfac- 

 tory series of the Silurian Eocks of Sweden, Dr. Linnarsson is able 



