44 Reports and Proceedings — 



Feet. 



(c) Birkhill \ ,,•. -p- -p- i i,-ii f Grey and purple flagstones, witli 



Shales, or j ^"^ ^^^^^ iiu'Kiiui j ^^^^^ ^^ ^^^^^ ^^^ ^^^.^^ ^^^^^^ ^^ ^^ g^ 



Upper I / \ T D- 1 vn f Black pyritous shales, with seams 



Moffat. ) ('') ^°^^^ ^^"^^^^ 1 of brightly coloured clays „ 60 to 70 



(o) Mar tf ell \ tt i^ n f Pale grey or green non-fossiliferous 



Shales, ox (5) Upper Hartf ell { j^u'-dstones ^ 45 



^^l ) («) Lower HartfeU Black hard slaty shales and flags 40 to 50 



(«) Glenkiln \ f Yellow and grey shales and flags, 



Shales, or I i non-fossiliferous, with a few 



Lower I j bands of soft black GraptoUtic 



Moffat. ; \ shales 150 



With the aid afforded by these sections, the thorough investiga- 

 tion of the ten subparallel black shale-bands of the Moffat area is 

 rendered a matter of ease and certainty. Of these, the four bands 

 lying to the south-west of Saint Mary's Loch are the most continuous. 

 They were described in detail by the author, and it was shown that 

 in each the only strata apparent are indisputably those of the type- 

 sections of Dobb's Linn and Craigmichan, with which they agree 

 zone for zone in sequence and in all their characters, mineralogical 

 and zoological. Here, also, the beds are arranged in greatly elongated 

 anticlinal forms, the axes of which are, as a rule, inverted. In any 

 single transverse section, the succession of the beds on the opposite 

 sides of the median line of the band is identical, and the highest 

 zone of the black shales everywhere passes up conformably into the 

 basal bed of the surrounding greywackes. The varying width of the 

 band is dependent simply upon the varying elevation of the crown 

 of the anticlinal. Where the band is of least diameter, only the 

 highest beds of the Birkhill shales rise from below the greywackes. 

 As the band expands, the underlying zones emerge one by one in 

 its centre, till finally, in the widest exposures, we recognize the 

 deepest strata of the Glenkiln shales. 



It was shown by plans, sections, and descriptions of every expo- 

 sure of consequence within the Moffat district that precisely similar 

 results are arrived at with respect to the remaining black shale- 

 bands. To the south of Moffatdale, the Moffat beds agree essentially 

 with those of Dobb's Linn ; but to the north the whole formation 

 diminishes in collective thickness, and the highest division gradually 

 loses its fossiliferous black shales. 



These facts place it beyond qixestion that all the carbonaceous and 

 Graptolitiferous shales of the Moffat area are portions of one and the 

 same originally continuous deposit — the Moffat Series, which is now 

 the oldest visible rock-group in the district, being everywhere in- 

 ferior to the prevailing greywackes, through which it invariably 

 rises from below in greatly elongated anticlinal forms. 



In the rigid restriction of distinct groups of fossils to a few feet 

 of the succession, the rocks of the Moffat series resemble the thin- 

 bedded Silurians of Scandinavia and North-eastern America. From 

 analogy it may be suspected that they similarly represent an enor- 

 mous period of time. The correctness of this inference is demon- 

 strated by the evidence afforded by the known geological range of 



