C. LAP WORTH ON THE MOFFAT SERIES 247 



the correlation of their subdivisions with their foreign equivalents, 

 would till recently have been practically impossible. In this con- 

 nexion I have been presented with many facilities denied to former 

 investigators. The valuable papers by Mr. Hicks on the sequence 

 and fossils of the various subformations of the Cambro-Silurian of 

 South Wales have been of especial service to me. From several 

 other eminent observers I have also to acknowledge most important 

 aid. To Mr. J. Hopkinson I am indebted for much of my know- 

 ledge of the Graptolithina of Wales. Professor H. A. Nicholson 

 placed at my disposal the results of his researches in the Lake 

 district. Dr. G. Linnarsson, of Stockholm, furnished me with a 

 complete summary of the facts hitherto collected by the Swedish 

 Survey with respect to the range of the Graptolithina in the Scan- 

 dinavian Silurians. Through the kindness of the three last-named 

 gentlemen I have been enabled to compare the organic remains of 

 the Moffat rocks species for species with those of their extra - 

 Scottish representatives. 



Much of the district under description was worked over in 

 company with my friend Mr. James Wilson ; and my study of the 

 fossils of the dark shales was greatly facilitated by the aid afforded 

 me by several observers who had already made collections from 

 these strata outside the limits of the Moffat district. Among others 

 I have especially to thank Mr. W. Swanston, of Belfast, and Messrs. 

 D. J. Brown and W. Dairon, of Glasgow. 



A. Physical Belations of the Moffat Series. 



§ I. (a) Description of the typical Section of Dobb's Linn. 

 (Plate XII. Sections I., II., III.) 



The only section of the Moffat Series which allows us to deter- 

 mine with certainty the sequence and palseontological characteristics 

 of its component beds, and at the time clearly exhibits the relation- 

 ship of the group as a whole to the surrounding greywackes, occurs 

 in the centre of the Moffat district, about midway along the longi- 

 tudinal depression already referred to. The highway from Selkirk 

 to Dumfries, which runs upon the floor of this depression, crosses 

 the main watershed at the spot marked by the little cottage of 

 Birkhill, and begins to descend the long straight valley of Moffat- 

 dale to the south-west, About half a mile below the cottage three 

 small streams of nearly equal volume meet at the same point to 

 form the infant Moffat. Two of these streams dash down the steep 

 slopes bounding the valley to the south-west ; but as they flow over 

 thick beds of hard grit, their courses are comparatively shallow and 

 insignificant. The third stream, however, which descends from the 

 north-west, emerges from a gloomy hollow dug deep in the flank of 

 the rugged ridge that shuts in the main valley to the north. 



Entering this hollow at its foot, it is seen to be a narrow rugged 

 gorge, deriving its forbidding appearance from the black shales that 

 close it in, and mount up on both sides in naked cliffs of great 



