Vol. 62.] TARANNOX SERIES OF TARANNON. 6~0 



(2) Western Area. 



We now turn to an examination of the sections which, lying to 

 the west of the main syncline, are exposed on the western slopes 

 of the tableland and in the open valley of the Twymyn, which flows 

 nearly due north in a direction parallel to the synclinal axis. 



At the northern end of the Tarannon district, along the valley of 

 the Iaen already described, we have seen that denudation has only 

 proceeded to an extent sufficient to expose the Talerddig Grits and 

 the underlying Gelli Beds. But in this western area it has laid 

 bare still older groups, extending down through the base of the 

 Tarannon Series into beds which are clearly of Llandovery (Brrkhill) 

 age. 



Unfortunately, the working-out of the descending succession is 

 rendered difficult by the effects of the lateral pressure to which the 

 strata have been subjected. The beds belonging to the lower 

 groups are softer and more yielding than those of the upper, and 

 they have therefore suffered to a greater extent from folding and 

 cleavage. Not only are they bent into sharp anticlines and synclines, 

 but the eastern limb of these folds is generally fractured, and in 

 some cases older beds have been thrust over newer. Nevertheless, 

 if we disregard the local complexity of detail, we can make out 

 the general succession of the beds as a whole, and we find that 

 continuously-older strata meet our view as we descend from the 

 high ground of the Tarannon tableland on the east, down to. the low 

 level of the Twymyn in the west. I will proceed first to describe 

 some of the rock-sections exhibited in the tributary streams of the 

 Twymyn along the western slope of the Tarannon tableland, 

 commencing with those at the southern end near Stay-a-little. 



(a) Sections of the Tarannon Series along the Western 

 Slopes of the Tableland. 



(i) District between Crygnant and Stay-a-little. 



The sections in the southern part of this western district are for 

 the most part short, and do not throw much light on the general 

 sequence ; but they exhibit several points of interest with regard 

 to the lithology and fauna of the individual rock-groups. 



Between Crygnant and Stay-a-little the Talerddig Grits make a 

 prominent feature, forming the crags of Pen Cerrig-y-ffyrmon, and 

 presenting a steep scarp-face to the valley of the Afon Bachog, 

 a tributary of the Clwyddog. All along this line are numerous 

 small streams, which have cut narrow but deep clefts through the 

 Gelli Shales. The rocks of the Gelli Group are here of the type 

 described in the Tarannon section, and consist of shales and 

 numerous small flags, with an occasional grit-band. The typical 

 Gelli graptolites, including Monograptus crispus, M. exiguus, 

 M. Marri, M. priodon, and M. nudus, were found just above a small 



