332 C. LAPWOKTH ON THE MOFFAT SEBIES. 



C. Conclusion. 

 § I. Systematic Importance of the Divisions of the Moffat Series. 



The black carbonaceous and ferriferous strata of the Moffat Series 

 have often been compared to the thin-bedded argillaceous deposits, 

 impregnated with iron and stained with vegetable matter, that bulk 

 so largely in our British Coal-measures. It is, indeed, impossible 

 to avoid this comparison. The rapid alternation of thin flaggy 

 layers of nodular ironstone and carbonaceous and partially calca- 

 reous strata give to many of its sections* (especially those of the 

 Birkhill division) a remarkable resemblance to hundreds that may 

 be pointed out in the higher division of the Carboniferous system. 

 These resemblances descend even to minute peculiarities. One of 

 the most striking is the frequent association of a seam of black 

 shale with a band of white or cream-coloured clay, which has been 

 very aptly instanced t as reminding the observer of a coal-seam and 

 its subjacent argillaceous floor or " under-clay." 



Several mining speculators, relying solely upon these mineralogical 

 resemblances, have sought in vain for coal in these beds. To the 

 geologist they have been equally misleading. Accustomed to the 

 rapid recurrence of strata of this nature in a great mass cf sandstone 

 rock, and finding, as it appeared, a similar arrangement almost 

 everywhere throughout the Silurians of the south of Scotland, he 

 could not fail to draw the inference that these black beds occurred 

 upon several horizons in an enormous mass of arenaceous deposits. 



In the case of the miner, an acquaintance with the geological 

 position of the fossils of the carbonaceous shales would have effec- 

 tually prevented his foolish expenditure of time and labour. Simi- 

 larly, in the case of the geologist, it is our present knowledge of the 

 vertical range of the fossils of the Moffat Shales which, above all 

 other testimony, proves their identity in character, sequence, and 

 physical relationships in every locality, clearing away at a single 

 stroke most of the difficulties that formerly barred the path of the 

 investigator, and rendering his task in the future a matter of ease 

 and certainty. 



Moreover it has shown conclusively that, beyond their superficial 

 lithological resemblances, the Moffat Series have no features in 

 common with the argillaceous and ferriferous Carboniferous strata 

 with which they are usually compared. The Coal-measures were 

 manifestly accumulated under what, geologically speaking, were 

 rapidly varying physical conditions. Beds precisely similar recur 

 again and again in the succession. The fauna remains unaltered 

 through enormous thicknesses of rock, the same species reappearing 

 invariably upon the resumption of similar physical conditions. On 

 the other hand, the Moffat Eocks, though composed merely of a 

 few hundreds of feet of black and variegated shales and mudstones, 

 rarely or never show two bands that are precisely similar ; nor do 

 they anywhere throughout the succession in the present district 

 afford the slightest evidence of hasty deposition. The collective 



* Mem. Greol. Surv. Scotland, Explan. Sheet iii. pp. 11, 12. 

 t Ibid. Explan. Sheet iii. p. 11. 



