THE B0RR0WDALE SERIES AND THE CONISTON FLAGS. 475 



corals which have been found are not such as to give any guide to 

 the age of the strata, all that can be said being that they belong to 

 a type not hitherto recognized in the underlying Coniston Lime- 

 stone. 



The clear evidence borne by the Crustacea, Brachiopoda, and Ce- 

 phalopoda as to the Lower-Silurian age of the Graptolitic Mudstones, 

 is still further substantiated when we consider the characters of the 

 Graptolites themselves, by far the most abundant fossils in this 

 series. Without entering into any minute analysis of the Grapto- 

 lites found in these rocks, it may at once be stated that they con- 

 stitute an assemblage of forms of an unequivocally Lower- Silurian 

 aspect. This is proved by the presence, in abundance, of represen- 

 tatives of the Diprionidian genera Diplograptus and Climacograptus, 

 by the remarkable variety of the species of Monograptus, and by the 

 presence of the genus Rastrites. At the same time, that the Grap- 

 tolitic Mudstones are not low down in the Lower Silurian series is 

 equally clearly shown by the total absence of the genera Didymo- 

 graptus and Dicranograptus. 



As regards the species of Graptolites, Climacograptus teretiusculus, 

 Diplograptus pristis, D. palmeus, D. tamariscus, Monograptus Sedg- 

 wickii, M. triangulattis, M. spinigerus, M. intermedins, M. gregarius, 

 M. Sagittarius, 31. fimbriatus, M. lobiferus, M. Nilssoni, Rastrites 

 peregrinus, R. distaas are all found in the Moffat shales of the south 

 of Scotland, and are more especially characteristic of that division 

 of the Moffat shales to which Mr. Lapworth has given the name of 

 the " Birkhill Group." Thus nearly three fourths, or seventy-five per 

 cent., of the total number of Graptolites known in the Mudstones, 

 including all the common and characteristic species of the group, 

 can be specifically identified with forms which serve to mark the 

 Lower Silurian rocks of the southern uplands of Scotland, the posi- 

 tion of which has never been questioned. 



Taking all the various fossils now known from the Graptolitic 

 Mudstones together, it is impossible to doubt that the balance of the 

 palaeontological evidence is overwhelmingly in favour of the view 

 that this formation is of Lower- Silurian age. 



Such being the case, the Graptolitic Mudstones must corre- 

 spond in position with the highest beds of the Bala series or with 

 the lower portion of the Llandovery group ; and this is the direction 

 in which we believe all the evidence tends. As to the precise physical 

 relations between the Graptolitic Mudstones and the subjacent 

 Coniston Limestone, we are of opinion that the two groups are 

 strictly conformable to one another. Not only are the Mudstones 

 invariably found in their proper position, resting upon the limestone, 

 as seen when there are sections of these groups, but no discordance 

 can be detected, as regards the dip and strike, between the two series 

 where they cannot be seen in actual contact. 



Moreover (and this appears to us to be an argument of the greatest 

 weight) it cannot be shown that there is any overlap of the Grap- 

 tolitic Mudstones upon the Coniston Limestone, the former always 

 resting, so far as we have seen, upon the highest bed of the latter. 



