140 THE ROCKS OP THE TOERJIAKEADT DISTRICT. [May I909, 



1. Arenig Beds. 



Mount Partry Beds. 



(c) Coarse quartzose grits with occasional chert-bands, and, towards 



the southern half of the area, tuffs. 

 (I) Fine grits, graptohtic slates, and cherts. 

 (a) Coarse conglomerates. 



Owing to the character of the Shangort Beds, there are very few 

 localities where the dip-angle can be obtained, and in consequence 

 their thickness is largely conjectural. The two places where one can 

 obtain an approximate estimate of it are respectively just south- 

 west of Gortbunacullin and west of the Smithy bridge. At both 

 these localities the Shangort Beds seem to be about 1000 feet 

 thick. 



The thickness of the red felsite is also a matter of extreme 

 uncertainty. On the assumption that it is dipping at the same angle 

 as the overlying Shangort Beds at the Smithy bridge, its thickness in 

 this region, where it is at its narrowest, is about 300 feet. Farther 

 north, however, there can be no doubt tbat the thickness is far 

 greater than this, although probably the extra breadth of the outcrop 

 may be partly due to a lower dip-angle, or to repetition by faulting 

 or folding. 



The Mount Partry (Arenig) Beds are well exposed in the Trean- 

 laur stream, and on the supposition that the coarse conglomerate, 

 in which no dips are obtainable, is dipping throughout in conformity 

 with the grits immediately in contact with it, a total thickness of 

 about 1300 feet of Arenig Beds is seen in this section. The coarse 

 quartzose grit, which is comparatively thin near Mount Partry, 

 is probably about 400 feet thick near Gortbunacullin. 



Intruded into these rocks are felsites, intermediate rocks of 

 andesitic type, hornblende-lamprophyres, and dolerites. These occur 

 in masses, for the most part, of very small extent ; but the felsite- 

 intrusion in the northern part of the area is of very considerable 

 dimensions. 



In conclusion, we wish to tender our most hearty thanks to 

 Mr. P. B. Cowper Peed for the large amount of trouble that he has 

 devoted to the examination of our generally very fragmentary 

 Llandeilo fossils. Our sincere thanks are also due to Dr. G. J. 

 Hinde, P.P.S., for examining the radiolaria, and to the Director 

 of the Geological Survey of Ireland for the loan of maps. Other 

 acknowledgments are contained in the body of the paper. 



