Ivi PKOCEEDIMGS OP THE CtEOLOGICAL SOCIETY, ^vol. Ixxvii^ 



the o-reat memoir on the Molt'at Series eommimieated to this 

 Society in 1877. In each of the numerous shale-bands which had 

 been thought to form successive horizons in an ascending series of 

 greywackes. he proved that there was a repetition of lithologieal 

 types, in some cases in normal, in others in inverted order. 

 Careful collecting of the graptolites. the only fossils, showed that 

 each lithologieal type was associated with a special fauna Avhich 

 accompanied it in all its repetitions and inversions. Three main 

 faunas were individualized and named after Glenkiln. Hartfell, 

 and Birkhill ; and, on comparison with all reliable s^raptolite 

 evidence in Britain and abroad, checked by his personal travels 

 and observations. Lapworth was able ultimately to correlate these 

 fossils with those known from the Upper Llandeilo, Bala, and 

 Llandovery Series respectively. Thus it was proved that a group 

 of line black shales, 200 or 300 feet thick, represented a vast 

 thickness of rocks elsewhere, and that the tectonics of the region 

 consisted of a series of inverted and faulted anticlines of the shales 

 peering out among synclines of the Gala greywackes. In spite 

 of the complicated stratigraphy, Lapwoi'th was able to publish 

 fully-measured sections, to subdivide the rocks into smaller groups, 

 and even in some cases to establish graptolitic zones which, with 

 triding modification, have now become the standard of comparison 

 throughout the world. 



In order to test his conclusions, he next took the G-irvan rocks 

 in liand — a series of great thickness and variety in lithology, and 

 rich in fossil content, which had been placed high up in the 

 supposed Upland sequence, and, despite their innumerable shells 

 and trilobites, had not been satisfactorily correlated with any 

 part of the 'Silurian' succession in England or Wales. Accurate 

 mapping and exhaustive fossil collection were again employed, and 

 in some of the intercalated strata graptolites were discovered. The 

 mapping, again on a large scale, of lithologieal t\'pes, checked by 

 the contained fossils and especiallv by the graptolite-bearing 

 bands, revealed the succession in an area of which the sb*ati- 

 gi'aphy was at least complicated as at Moifat. It also showed 

 that the graptolitic bands occurred in the same order as before. 

 It became, therefore, possible to ascertain the relationship between 

 the graptolite faunas and the intercalated shell and trilobite 

 faunas, and to set up in Scotland a fully investigated standard of 

 comparison with ' Silurian " rocks of the type areas of England 

 and Wales. 



