338 C. LAPWORTH ON TELE MOFFAT SERIES, 



and schists of Bala age, and only a few survive into the overlying 

 Retiolites-be&s (Mayhill?). 



Similar facts might be cited from Brittany, Spain, Ireland, &c, 

 but no further evidence is required to prove that the Birkhill Shales 

 are of Lower Llandovery age. 



§ III. General Conclusions regarding the Age, Geological Relation- 

 ships, and Conditions of Deposition of the Three Divisions of the 

 Moffat Series. 



1. The evidences actually at our command regarding the vertical 

 distribution of the fossils of the Moffat Series in the Silurian rocks 

 of Europe and America thus conclusively establish the high syste- 

 matic importance of its three main divisions, already deduced by 

 us from their general lithological and palgcontological characteristics. 

 The three faunas which in South Scotland are characteristic of the 

 three successive Divisions of the Moffat Series prove to be elsewhere 

 as strikingly characteristic of the three successive formations that 

 form the upper portion of the Cambro-Silurian system. 



2. At the same time it cannot fail to be noticed that the vertical 

 distribution of the Graptolithina among the Silurian rocks of the 

 southern portion of Britain, Scandinavia, Central Europe, and North 

 America agrees exactly in all the common forms, species for species, 

 with that worked out by us in our detailed study of the black shales 

 of the Moffat district. We are thus furnished with a complete 

 palseontological demonstration of the truth of our interpretation of 

 the geological succession in the Moffat Series. 



3. In future the Glenkiln Shales must be considered as the equi- 

 valents of the highest division of the Llandeilo formation of Siluria ; 

 the Hartfell Shales as the attenuated representatives of the Bala or 

 Caradoc formation ; and the Birkhill Shales as standing in the place 

 of the Lower Llandovery. 



The lower portion only of the Hartfell Shales appears to be re- 

 presented among the extra-Scottish Graptolitiferous deposits, and 

 invariably by strata inferior in geological position to the Bala Lime- 

 stone. If this be true, the Upper Hartfell Shales must occupy 

 approximately the place of the Bala Limestone of Wales and its 

 foreign equivalents. 



The Birkhill Shales have been shown to belong to the lower half 

 of the Middle Silurian (Llandovery formation of Murchison). If, 

 therefore, the plan of making the Upper Silurian commence at the 

 base of the Lower Llandovery, as advocated by Sir Charles Lyell, 

 Mr. Hicks, and others, be generally adopted, the line of demarcation 

 between the Hartfell and Birkhill Shales must form the uppermost 

 limit of the Lower or Cambro-Silurian of the south of Scotland. 



4. It may be objected by those who are familiar with the Upper 

 Llandeilo, Bala, and Lower Llandovery formations of Wales, where 

 each of these formations is composed of several thousands of feet of 

 varied rock-matter, and characterized by a very diversified fauna, 

 that it is highly improbable that they can have so degenerated in the 

 insignificant geographical interval which divides Siluria from the 

 south of Scotland, as to be represented in the latter region only by 



