Fearnsides, Elles, Smith — Pakeozoic Rocks of Tomeroy. 113 



Structure of the Bistrict. 



Though our work on the Poraeroy district is in some respects 

 only an amplification and extension of the work begun by Portlock, 

 the views expressed in this section are at variance with those put 

 forward by all previous writers. According to our interpretation 

 of the evidence, the structure of the Pomeroy area resembles that 

 of the Moffat district of South Scotland, and the thickness of beds 

 involved is correspondingly small. Portlock supposed it to be 

 3500 feet ; but the present authors can arrive at no higher figure 

 than 500, or at the most 600 feet. Of this they allow about 

 100 feet to the basal Bardahessiagh beds, and another 100 feet to 

 the fossiliferous flagstones above. The Killey Bridge beds probably 

 include nearly another 100 feet; and the Corrycroar group is exposed 

 to the extent of perhaps 150 feet, leaving 150 feet to include the 

 whole of the Little Biver group and Tirnaskea beds. If this be so, 

 and the dip be fairly constant at 30° to 50° to the south or south-east, 



Fig. 1. 



Diagrammatic Section across the Pomeroy District. 



the three to four miles of outcrop in a direction tranverse to the 

 general strike demands explanation. Our explanation is that the beds 

 are strongly folded in innumerable shallow isoclinal folds, which are 

 more or less turned over towards the north, and in some of which the 

 middle limb has been replaced by a fault. AVe may represent our views 

 of the structure diagrammatically (fig. 1), and we may compare this 

 diagram with the somewhat idealized section which we have been able 

 to draw to show the actual relations of the rocks as seen along a line 

 from Craig Bardahessiagh on the north, to the hill of Tirnaskea on the 

 south, crossing the best-exposed portions of the district (fig. 2). 



The best evidence, however, is furnished by the distribution of the 

 various beds brought out by the mapping. The most accessible and 

 convincing section is that afforded by the bed of the Little Biver 

 between the Pomeroy-Bardahessiagh bridge and the Slate Quarry, 

 where, in the space of somewhat less than a mile, some thirty or forty 

 anticlinal cusps with quaquaversal dips appear in the stream. The 



K.I. A. I'ROC, VOL. XXVI., SEC. B. 



