﻿1850.] HARKNESS ON THE SILURIANS OF DUMFRIESSHIRE. 51 



and having intercalations of compact, bluish-grey greywacke, of an 

 almost semi-metallic aspect. In this bed obscure traces of organisms 

 occur. Besides the small concretionary bodies like Cythere (as at 

 Greskin and Craigmichean Scarrs), there are also sinuous markings, 

 and, in considerable abundance, long, thin, nexuous, tapering bodies. 

 The Graptolites here are well-marked and abundant ; the individuals 

 of some of the species are of a large size, one being traced through 

 several fragments of shale for more than 18 inches without showing 

 either of its extremities. They do not, however, occur in the bed 

 which affords the concretions and markings, but are confined to the 

 earthy shales. The dip of the deposits here is the same as that 

 which commonly prevails, viz. towards the N.N.W. at a high angle. 

 Of this line of anthracite and graptolitic shale we have no further 

 traces after it passes under the red sandstone at Bell Craig Linn. 



General Remarks on the Anthracite and Graptolite Beds. 



From the foregoing description of the position of these anthracite 

 beds and graptolite shales, and the direction which they take, it will 

 be seen that three distinct and well-marked courses occur in the 

 county of Dumfries. These bands are in a great measure parallel to 

 each other, the average distance between the bands being about two 

 and a half miles, and although they cannot be traced to the same 

 extent, it is probable that their relation to each other is such, that 

 they were originally portions of the same deposit. 



Of the most northerly band, from the point where it makes its 

 appearance in Dumfriesshire to the locality where it is lost sight of, 

 the distance is about twelve miles in a direct line. The second tra- 

 verses an extent of about twenty miles between Dobbs Linn and the 

 Glenkiln Burn. If, as I think, it be the same which reappears 

 again in Kirkcudbright, and passes through that county for more 

 than twenty miles, its course can be traced for about fifty miles, in- 

 cluding the interval which occurs between Glenkiln and Shawhead, 

 in which it runs under the red sandstone of the lower portion of the 

 vale of the Nith. The extent of the southerly band is much less 

 than either of the other two, not exceeding five miles ; but, as this 

 one disappears under the red sandstone of the higher part of Annan- 

 dale, and, if it reappears again on the opposite side of the vale, must 

 occur amongst a series of Silurian rocks, considerably metamorphosed, 

 its course as an anthracite bed and graptolitic shale must be much 

 shortened westward. The length of these lines on the east, beyond 

 the county of Dumfries, I have not yet been able to ascertain, not 

 having examined the geology of Selkirkshire ; but, from their ap- 

 pearance when they enter Dumfriesshire, it is probable that they 

 traverse the whole of the country lying eastward, and their persist- 

 ency is such, that it is by no means unlikely that they run through 

 the whole of the Silurians of the south of Scotland, except when 

 igneous rocks have interfered. 



The position of these bands is probably attributable to a succes- 

 sion of faults, which run through the district in a direction parallel 

 to the strike and range of the chain. The section at Glenkiln Burn 



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