662 MISS E. M. K. WOOD ON THE \_~NoV. I906, 



Graptolites were obtained at various localities, the species being the 

 same as those cited above. 



A few yards below the point where a small stream enters the river 

 on the left bank, two well-marked grits, of 16 inches and 2 feet 

 in thickness respectively, are seen ; and, in a thin dark shale-band 

 above them, the following graptolites were found in abundance and 

 in a fair state of preservation : — 



Monograptus crispus (0). 

 Monograptus priodon (C). 

 Monograptus nudus (f. 0). 



Monograptus discus (R). 

 Monograptus turriculatus (v. R). 



These grits are of some stratigraphical importance, as they may 

 be recognized at other localities and mark a definite horizon in the 

 Gelli Group. 



Descending the river for about 80 yards, one may see another 

 fold well exhibited in the left bank. The beds are much contorted, 

 and are penetrated by quartz- veins in all directions, while the shales 

 below the fold are cleaved. The strike of the cleavage coincides 

 with that of the beds, and is about 50° east of north ; while its dip 

 is about 20° higher than that of the beds, which is 35°. 



The last locality at which Monograptus crispus" ajadi its associates 

 were obtained in this Tarannon-River section is 140 to 150 yards 

 below this fold, and almost due east of the farm of Graigwen. The 

 beds here consist of dark-grey banded mudstones, which weather to 

 an orange tint. The base of the Gelli Group is drawn provisionally a 

 short distance to the south of this locality, at a point some 150 yards 

 above the footbridge south of Graigwen : because below this point 

 we find that there is a gradual but distinct change, both in the 

 lithology and in the fauna of the deposits. 



Reviewing the graptolitic fauna of the Gelli Group, we find that 

 it contains eight species, of which five are common to the Talerddig 

 Beds above. M. crispus is, so far as known, restricted to these Gelli 

 Beds, and is characteristic of them, not only in this section but else- 

 where in the district. The Gelli Group may, therefore, be referred to 

 as t h e Mo nogr ap tus-crispus Beds. M. discus and M. su bconicus 

 occur both in the Gelli and in the Talerddig Groups, but are distinctly 

 less abundant in the lower beds. M. ccciguus, M. turriculatus, and 

 Petalograptus palmeus var. tenuis, which occur in the Gelli Beds, 

 are unknown in the Talerddig Grits above, but pass down into the 

 Brynmair Shales below. Of these graptolites, however, M. turri- 

 culatus is extremely rare, only one specimen having been found. 



(iv) Brynmair Shales and Mudstones (Ba). 

 (Zone of Monograptus turriculatus.) 



Below the Gelli Shales we enter upon a new group of strata, that 

 is, on the whole, distinctly less sandy, and consists almost entirely of 

 soft shales and mudstones, which have consequently suffered to a 

 considerable extent from the effects of folding and cleavage. While 

 the exact order and limits of these beds cannot be fixed, yet a 



