340 C. LAPWORTH ON THE MOFFAT SERIES. 



In brief, the vertical dimensions, lithology, and palaeontology of 

 the Lower Silurian rocks of Western Europe and Britain are prac- 

 tically invariable when the beds are followed in a N.E. and S.W. 

 direction; while they change simultaneously, and to a large but 

 progressive extent, in all these characters when they are traced from 

 south-east to north-west. The geologist, therefore, aware of these 

 facts, might safely have inferred a priori that the Llandeilo, Bala, 

 and Lower Llandovery deposits of the south of Scotland, which lie 

 in the general line of strike of the Scandinavian Silurians, would, 

 in all probability, resemble them in their essential features. This, 

 as we have seen, is undoubtedly the case ; and the Moffat Series can 

 therefore no longer be regarded as in any way anomalous. On the 

 contrary, they are very naturally defined as British Silurians of the 

 Scandinavian type, being simply the south-westerly prolongation of 

 the sheet of dark Graptolitic schist, of whose vertical continuity the 

 prolific Lower Silurian Limestone bands of Sweden are brief and 

 local interruptions. 



5. The consideration of the physical and zoological relationships 

 of the rocks of the Moffat Series to those of the equivalent Silurians 

 of Girvan, the Lake-district, and the north of Ireland is best 

 deferred till the exposures in the Lammermuirs, Leadhills, and 

 Galloway have been described in detail and all the facts are before 

 us. Nevertheless it is perhaps allowable in this place to call 

 attention to the highly significant facts of the remarkable litho- 

 logical homogeneousness and insignificant vertical thickness of the 

 Moffat Series in the district already described, together with the 

 perfect identity in type of its successive faunas, so clearly distinct 

 specifically. For these facts there appears to be but one common 

 explanation. They point almost irresistibly to the conclusion that 

 these strata must have been laid down in an area removed in some 

 way from the irregular and disturbing influences of river-deposits 

 and current-action, and in which the general physical conditions of 

 the sea-bed remained practically unaltered from the middle of the 

 Llandeilo to the close of the Lower Silurian epoch. 



§ IY. Bearing of the foregoing Conclusions upon the general Question 

 of the Succession among the Lower Silurian Rocks of the South of 

 Scotland. 



It only remains in conclusion to indicate as briefly as possible the 

 bearing of the foregoing results upon the general question of the 

 succession among the Lower Silurians of the south of Scotland. 



In this connexion it is highly satisfactory to observe not only that 

 our conclusions appear to be in complete accordance with all the 

 facts universally admitted among those who have made these rocks a 

 subject of special study, but that at the same time they furnish us 

 with a thorough elucidation of many strange anomalies which have 

 hitherto sorely perplexed the cautious investigator. 



(a) All the black bands yet detected among the Scottish Silurians 

 contain fossils of identical species and varieties with those afforded 

 by one or other of the zones of the Moffat Series, as described in the 



