Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/275

 as Scotland itself is concerned, a considerable number of the Upper Llandeilo Graptolites continued to exist in their own area, though a still larger number became extinct. The remains of those which survived are found in a great series of rocks superior to the Dumfriesshire Shales and also to the Bala Limestone (Wrae Limestone), to which their discoverer, Mr. Charles Lapworth, applied the name of the " Gala Group." Regarding the Gala group, for the present, as a single series of deposits, the following Table exhibits the chief Graptolites which are known to occur in it.

Graptolites of the Gala Group.

Derived from the Upper Llandeilo of the Scotch area.

Climacograpsus teretiusculus, His.

Diplograpsus pristis, His.

Rastrites Linnsaei, Barr.

Graptolites Sedgwickii, Portl. .

— — Nilssoni, Barr. — — lobiferus, M' Coy.

— — sagittarins, His.

Retiolites perlatus, Nich.

Derived from the Coniston Mudstones.

Graptolites exiguus, Nich.

— — priodon, Bronn.

— — colonus, Barr.

— — turriculatus, Barr.

Retiolites Geinitzianus, Barr.

It appears from this list that the Gala group has yielded thirteen species of Graptolites, of which eight, or over sixty per cent., are identical with species of the preexistent Upper Llandeilo area. The diprionidian species of the genera Climacograpsus and Diplograpsus I give on the authority of Mr. Lapworth ; but they have not come under my own notice, and they seem to be certainly absent from the higher part of the Gala Group. We have also to notice the absence in the Gala group, as in the Coniston Mudstones, of any representatives of the genera Didymograpsus, Dicranograpsus, Coenograpsus, and Pleurograpsus. The remaining five species of the Graptolites of the Gala group are not survivors of the Upper Llandeilo fauna, but are all found in the Coniston Mudstones, and appear, therefore, to be importations from the Coniston area of the North of England.

The data at present in my possession do not enable me to speak positively as to the further career of the Graptolites of the Gala group. So far as is known to me, the only survivors of this period were Graptolites colonus, G. priodon, and Retiolites Geinitzianus, of which the two former occur in the Wenlock rocks of Kirkcudbrightshire, whilst the two last mentioned occur in the Ludlow rocks of the Pentland hills.

E. HUDSON-RIVER AREA OF NORTH AMERICA. — The greatest migration of the Upper Llandeilo Graptolites of the south of Scotland appears to have taken a westerly course, and to have ultimately reached the United states, forming the well-known Graptolitic fauna described by Hall as occurring in the Hudson-River Shales and Utica Slates (Caradoc).

The grounds for this belief I will state immediately ; but I may