228 



PBOCEEDIKGS OF THE GEOLOGICAL SOCIETY. [Feb. 21, 



in the meanwhile introduce a Table of the Graptolites of these for- 

 mations. 



Graptolites of the Iladson-lUvet' Shales and Utica Slates. 



Diplograpsus prist! s, His. 



mucronatus, HalL 



■ AVhitfieldi, Half. 



angustifolius, Hall. 



Climacograpsus bicornis, HalL 



■ teretiuscuhis, His. 



Dicranograpsus rainosus, Hall. 

 Didymograpsiis sextans, Hall. 



divaricatus, Hall. 



flaccidus, Hall. 



Cainograpsus (Helicograpsus) gracilis, Hall. 

 Graptolites Sagittarius, His. 



tenuis, Portl. (?) 



Didymograpsus serratulus, Hall. 

 Diplograpsus putillus, Hall. 



■ quadrimucronatus. Hall. 



Climacograpsus tjpicalis. Hall. 

 Dicranograpsus furcatus. Hall. 

 Eastrites Barrandi, Hall. 

 Ketiograpsus eucharis, Hall. 



Geinitzianus, Hall. 



Dichograpsus(?) multifasciatus, Hall. 



] 



Derived from the Upper 

 Llandeilo of the south 

 of Scotland. 



Derived from the Skiddaw area ? 



Not occurring in the Upper Llan- 

 deilo, and all, except the first, 

 peculiar to tliis formation. 



It appears from this list that, excluding- some doubtful forms, 

 there are twenty-two species of Graptolites known from the Hudson- 

 River group and Utica Slates. The grounds upon which we may 

 assume these to have been mainly introduced into America bj^ migra- 

 tion from Scotland are as follows: — 1. Of the abundant types of 

 Graptolites in the older formation of the Quebec group of Canada 

 not one single species occurs in the Hudson-Eiver group ; whilst 

 there is preserved but one of the peculiar genera of the former, and 

 that is represented by but one species {Dkhograjisus 1 multifasciatus). 

 It is clear, then, that a great extinction of Graptolites took place at 

 at the close of the Quebec period ; and we cannot look to the rocks 

 of this group as the source of the Graptolites of the Hudson-Eiver 

 area. 2. Of the total of twenty-two species of Graptolites know^u 

 from the Hudson-Eiver group, no less than thirteen, or nearly sixty 

 per cent., are spedjicaTli] identical with forms which occur in older 

 deposits of the Upper Llandeilo area of the south of Scotland. 3. At 

 least seven of these thirteen species have been detected by Mr. Baily 

 in strata of C'aradoc age in Ireland ; and we may well believe that 

 Ireland constituted an intermediate station in the migration of these 

 species from Scotland westwards. 



It should be noticed also that this great westward migration of 

 the Upper Llandeilo Graptolites of the south of Scotland led to the 

 preservation into the Caradoc period of the genera Bidymograpsus, 

 Dicranograpsus, and Ccenograpsus. These three genera, namely, 

 seem to have failed to make their way southwards; they are 

 wanting in the Conistou Mudstones, whilst they died out in their 

 own area, and are not to be foimd in the Gala group ; they are to 



