Distribution uf the Rhabdo-phvi'a. 365 



(C) Upper Birkhill. — This division, the most varied in its 

 mineralogical character and its included species, has also the 

 widest geographical extension. To it belong the graptoliti- 

 ferous shales of the so-called Lower Llandovery of Cardigan, 

 recently examined by Prof. Keeping, and also the disputed 

 graptolitic mudstones of the Coniston area of Westmoreland. 

 Elsewhere its representatives are recognizable in Girvan, 

 County Down, in the typical Lobife7-us-heds of Scania, in the 

 Alaunschiefer of Germany, and in the Colonies and the band 

 E e 1 of Bohemia. 



In all these widely separated regions the fauna is most dis- 

 tinctly of the type of that of the Upper Birkhill shales. In 

 this group, in the typical localities near Moffat, we recognize 

 three fairly distinct zones, the lowest characterized by Cepha- 

 lograptus conieta, Geinitz, and some survivals from the under- 

 lying M.-gregarius zone — and the upper distinguished by 

 Rastrites maximus, Carr., and by a few species which become 

 much more abundant in the overlying Gala beds. 



Generally speaking, these Upper Birkhill beds, in the whole 

 of their range from Cardigan through Northern and Central 

 Europe, are particularized by the preponderance of Monograp- 

 tidse of the genera Rastrites and Monograptus (both of which 

 probably attain their specific maximum upon this horizon), and 

 by the exclusive presence of such forms as Monograptus Hisin- 

 geri, Carr. (jaculum), M. intermedins, Carr., M. crenularis, 

 Lapw., and Diplograptidse of the type of Diplograptus 

 Hugkesi, Nich., Cephalograptus cometa, Geinitz, &c. 



A few of the commonest forms pass onwards into the strata 

 of the succeeding Upper Valentian or Tarannon group. Of 

 these the chief are Climacograp>tus normal is, Lapw., Diplo- 

 graptus palmeus, Barr., D. folium, His., and some forms of 

 Monograptus Sedgwickii, Portl. 



Gala or Tarannon Group. 



Mineralogically the distinction between the Gala group and 

 the underlying Birkhill series is most marked ; but palseonto- 

 logically there is an insensible gradation from the one into 

 the other. The Birkhill beds consist of black shales of no 

 great vertical extent, while the Gala series is formed of grey 

 conglomerates, flagstones, and shales of enormous collective 

 thickness. It is more than doubtful, however, if the Gala 

 group at all approaches the Birkhill beds in systematic im-| 

 portance. It must be looked upon at present as a transitional 

 formation — its lower beds graduating zoologically into the 

 inferior Birkhill beds, and its higher zones passing insensibly 



Ann. (0 Mag. Nat. Hist. Ser. 5. Vol. v. 25 



