344 



C. LA? WORTH ON THE MOFFAT SERIES. 



Discussion. 



Mr. Warington W. Smyth inquired as to the great break described 

 by the author as occurring at the limestone shown in the sections, 

 where it appeared that above the limestone there were forty or fifty 

 species which do not extend downwards, and below it forty or fifty 

 species which do not pass up. He wished to know whether this 

 indicated a real break in the life of the period, or whether it was 

 due to imperfect investigation of the deposits. 



Mr. Hicks remarked on the evident difficulty of the ground 

 investigated, and said that, without the combination of the thorough 

 knowledge of Graptolites and the keen perception of petrological 

 characters possessed by the author, such an explanation of its 

 structure as was given in his paper would have been impossible. 

 He remarked that the great folds described were not uncommon in 

 Silurian countries, and that the succession of rocks described was 

 similar to, if not identical with, that occurring in Wales and in the 

 Lake -district. The break at the Coniston Limestone indicates a 

 change in the physical history of the earth at that period, and is the 

 first break we know of after the commencement of the Cambrian. 



Mr. Carrtjthers remarked that many years ago he had been 

 thoroughly acquainted with, the district described, and had pointed 

 out that the Graptolites in this region were of very local occurrence, 

 and often strictly confined to particular beds ; but his geological 

 knowledge was not at the time sufficient to warrant him in at- 

 tempting to work out the stratigraphical results of his observations. 

 From his knowledge of the district, however, he felt convinced that 

 the author had offered a most simple and satisfactory explanation of 

 its excessively complicated structure. He thought that in Mr. 

 Lapworth's paper we shall obtain a base-line for the correlation of 

 all the Silurian beds of the south of Scotland. 



Prof. Ramsay wished to indicate that there was another side to 

 the question. Prof. Geikie and his assistants in the Geological 

 Survey of Scotland had observed the occurrence of the black shales 

 referred to ; but in Lanarkshire they recognized the existence of a 

 set considerably higher in the series than the Moffat shales, and 

 separated from them by a considerable thickness of shales and grits. 

 In Shropshire and Wales there is a great leap from the Caradoc to 

 the Upper Llandovery, and it seemed to him that part of the Scotch 

 beds, which contain a remarkable mixture of Lower and Upper Silu- 

 rian Mollusca, might represent the deposits missing in the more 

 southern area. 



Prof. Judd remarked that only by such careful and detailed 

 palaeontological investigations as those of the author was it possible 

 to hope to find a key to the true succession of strata so folded, 

 crumpled, and broken up as those of the Silurians of the South of 

 Scotland. 



Prof. Hughes pointed out that if Mr. Lapworth got the whole 

 series in one continuous section, as indicated on the wall, it was 

 extremely improbable that great grits should be intercalated close 



