226 PEOCEEDISGS OP THE GEOLOGICAL SOCIETY. [Feb. 21, 



a migration in a reverse direction from the Coniston area into the 

 Scotch area. 



It may be admitted, then, that the fundamental elements of the 

 Graptolitic fauna of the Coniston Mudstones were derived from Scot- 

 land ; but this fauna nevertheless has its own peculiar species, whilst 

 the absence of some of the Scotch forms is very remarkable. Thus 

 no traces have ever been discovered in the Coniston mudstones of any 

 species of the genera Bidymograpsus, Bicranograpsihs, Ccenograpsus 

 ( = ]Ielicograpsus) and Pleurograpsus, so characteristic of the Upper 

 Llandeilo area of the south of Scotland. On the other hand, there 

 is a great development of the species of the genus Graptolites in the 

 Coniston Mudstones, as compared with the Dumfriesshire Shales. 



It may be as well to follow out here the further course of the 

 Graptolites of the Coniston area. Immediately above the Coniston 

 Mudstones comes a great series of rocks to which the name of 

 "Coniston Flags"* was applied by Professor Sedgwick; and these 

 in turn are surmounted by a stiU more extensive group termed the 

 " Coniston Grits " by the same observer. The latter formation is 

 certainly Upper Silurian, as has been shown by Mr. Hughes ; and 

 the former may very possibly also belong to the Upper Silurian 

 period. Be this as it may, both formations contain Graptolites, often 

 in considerable abundance as far as individuals are concerned ; but 

 there is here a wonderful diminution in the number of genera and 

 species, as compared with the Coniston^ Mudstones. Thus the genera 

 Dlplograpsus, CUmacograpsus, and Rastrites, abundantly represented 

 in the Coniston Mudstones, are wanting altogether in the Coniston 

 Flags and Grits, in which there remain only the genera Graj)toUtes 

 and Betiolites. One or two new forms of the genus Oraptolites 

 are present ; but the commonest forms are G. priodon, G. colonus, 

 and Betiolites Geinitzianus, aU of which existed in the Coniston 

 Mudstones. 



It is clear, therefore, that the close of the period of the Coniston 

 Mudstones was signalized in the north of England by the setting-in 

 of conditions unfavourable to the existence of Graptolites. Of the 

 twenty-nine species in the Mudstones, only three pass upwards into 

 the immediately superjacent Flags, and the remaining twenty-six 

 become, so far as this area is concerned, extinct. We shall see, 

 however, that a considerable number of these were not absolutely 

 extinguished, but that they migrated, a few northwards into Scot- 

 land, and the larger number in a south-east direction towards 

 Bohemia. 



D. Gala area of the SoiiTn of Scotland. — Eeturning now to 

 Scotland, I may endeavour to trace out the further dispersal of the 

 Graptolites of the Upper Llandeilo area of Dumfriesshire. So far 



* In my paper "On the Graptolites of the Coniston Plags" (Quart. Journ. 

 Geol. Soc. vol. xxiv.), I incUided under the name of " Coniston Flags " both the 

 Coniston Mudstones and the overlying Coniston Flags proper. The researches, 

 however, of my friend Mr. T. McKenny Hughes, combined with my own inves- 

 tigations, have satisfied me that the two formations must be separated upon 

 paltTBontological grounds, though no physical break has yet been shown to exist 

 between them. 



