120 



PKOCEEDINOS OP THE GEOLOGICAL SOCIETY. 



and, adopting the views of Mr. Lapworth, from the absence of 

 Didymograptus Murcliisoni and the genus Phyllograptus in the black 

 shales of the Tremadoc area, and the presence of some succeeding 

 Bala forms, we may infer that these dark Tremadoc shales and the 

 Glenkiln beds are probably of higher-Llandeilo age. This inference 

 is further strengthened by researches made by Linnarsson in the 

 Llandeilo strata " of Central Sweden, where the greater portion of 

 the Llandeilo formation of Britain is represented by the Ortlioceras- 

 limestone." " Upon this limestone rests the sheet of dark shales 

 named by Dr. Linnarsson the ' Middle Graptolite schists the 

 lowest part of these schists, according to Dr. Tornquist, affords 

 abundant examples of Phyllograptus and the Murchisoni form of 

 Didymograptus. The highest Swedish beds assigned or referable to 

 the Llandeilo formation afford both the peculiar Scotch or Glenkiln 

 and North-Wales forms, such as Didymograptus superstes, Lapw., 

 Comograptus gracilis, Hall, Climacograptus Scharenbergi, Lapw., G. 

 perexcavatus, Lapw. 



Mr. Lapworth further discusses the relations and affinities of the 

 Llandeilo species of South Scotland (Glenkiln Shales) with the dark 

 shales and flagstones of the Cincinnati group which bound the valley 

 of the Hudson near the city of Albany and everywhere underlie 

 the Trenton limestone ; he shows reason for believing that we 

 may regard them as forming the " highest division of the Quebec 

 group (Arenig) which emerges unconformably from below the hori- 

 zontal Trenton limestones. The Hudson-Eiver shales may therefore 

 represent the higher Llandeilo beds of Britain." Lapworth names 

 14 species collected from Norman's Kiln in the valley of the Hudson, 

 on the Marsouin river, &c, as being identical with the Glenkiln and 

 "Welsh forms. He still further establishes representative affinity 

 between the peculiar Glenkiln species which are absent from the 

 American strata and others which occur in them. Thus : — 



British. American. 



Glossograptus Hincksii is represented by Glossograptus ciliatus, Emm. 

 Dicranograptus ziczac „ „ Dicranograptus fureatus, Hall. 



Climacograptus Scharenbergi ,, Climacograptus scalaris, His. 



Clathrograptus cuneiformis „ Claihrograptus Geinitzianus, Hall. 



" All evidence, therefore, tends to prove that the Glenkiln shales 

 belong to the age of the Upper Llandeilo series, and are closely allied 

 to the North-Wales grouping." From the absence of certain Didy- 

 mograpti and Phyllograpti from the Glenkiln division, and their 

 abundance in the lower beds of the Llandeilo of Wales and Sweden, 

 we are obliged to assign the Scotch Glenkiln Bhabdophora " to the 

 highest division of the Llandeilo, and not far below the base of the 

 Caradoc or Bala"*. 



It is of the Hydrozoa, Crustacea, and Brachiopoda, which together 

 make up the 123 out of the 175 known species, that the mass of 

 the fauna of the Llandeilo is composed. The same classes largely 

 transmit their genera and species to the succeeding Caradoc or Bala 



* For an exhaustive paper upon the Graptolites of the Moffat series, by 

 C. Lapworth, Esq., F.Gr.S., see Quart. Journ. Geol. Soc. vol. xxxiv. pp. 240-343. 

 The general characters of the Lower Silurian rocks of Scotland and the strata of 

 the Moffat district are also ably discussed. 



