C. LAPWOETH OS THE MOPPET SERIES. 299 



ture, and more or less alteration which these strata have undergone, 

 the physical, mineralogical, and palseontological evidences at our 

 command make it clear that in every intelligible section the natural 

 sequence of the beds is identical with that in our typical section at 

 Dobb's Linn. To the south of the Moffat valley this agreement is 

 so exact that the sections can be compared bed for bed and fossil 

 for fossil. To the north of the Moffat valley the dark fossiliferous 

 seams gradually die out of the highest grey-shale group, which 

 towards the north-west degenerates into a group of barren flag- 

 stones, undistinguishable from those which alternate with the sur- 

 rounding greywackes. 



So distinct and persistent, however, are the generality of the 

 various Graptolitiferous zones in their essential characters, litholo- 

 gical and palseontological, that, as we have seen, they admit of im- 

 mediate identification in every locality where they have not under- 

 gone excessive metamorphism. By an examination of their physical 

 arrangement in numerous transverse sections, and by tracing them 

 from point to point along the line of strike, we have assured our- 

 selves of the fact that in every extended band of black shale, after 

 the effects of the numerous faults have been allowed for, the order 

 of the beds on both sides of the central line of the band is precisely 

 similar. Where the main axis of the band is uninverted, the ter- 

 minal zones on the opposite margins pass visibly below the surround- 

 ing greywackes. Broadly speaking, where the black-shale band is 

 of small diameter, only the higher beds of the Birkhill Shales are 

 apparent. As it increases in width the underlying zones emerge 

 one by one in its centre; until finally, in the widest exposures, 

 we meet with the deepest visible strata of the Glenkiln Shales. 



We have, in addition, not only been able to satisfy ourselves of 

 the fact that all the rocks of the district have been crumpled up in 

 a large number of inverted folds, but we have even found it possible 

 to trace the geographical position of several of these plications, and 

 to measure approximately the amount of inversion. We have 

 ascertained that this inversion is sometimes so intense that, as in 

 the case of the Ettrick band, the overturned strata overhang the 

 vertical to such an extent that at first glance they appear to be 

 almost flat ; at other times it is so variable in its direction that, as 

 in Dobb's Linn, the plane of the inverted anticlinal oscillates as 

 much as 30° on opposite sides of the perpendicular in less than 200 

 yards. 



While therefore, on the one hand, the facts now at our command 

 make it clear that all evidence derived from broad views of the ap- 

 parent order of superposition of the strata within the present dis- 

 trict, unless confirmed by other testimony, is not only useless but 

 misleading, yet, on the other hand, they are amply sufficient to 

 enable us to disentangle the complicated succession among the 

 Moffat Shales themselves, and to establish the general identity of 

 the surrounding and overlying greywackes. 



The more important conclusions to which these facts inevitably 

 lead us may be very briefly summed up as follows : — 



x2 



