220 C. CALLAWAY 0^ THE ARCHiEAN 



quartz- schist between this rock and the grey gneiss ; but I cannot 

 affirm its presence. 



3. Area south-east of Paris Mountain. — The gneissic rocks of this 

 district are on the north-easterly prolongation of the strike of the 

 central zone ; and there is no doubt that they belong to the same 

 series : the dip, the succession, and the prevailing rock-types are 

 the same. 



On the coast between Dulas Bay and the fault north of Porth 

 lygan the succession is not satisfactory, owing to great disturbance. 

 South of Porth lygan the shore is mainly occupied by sandstones 

 and conglomerates, presumably of newer Palaeozoic age, deposited 

 on an eroded surface of gneiss, and sometimes wrapping round little 

 promontories of the older rock. The prevailing dip is easterly. On 

 Porth lygan the gneissic series is well exposed. Grey gneiss, dark- 

 green schist, granitoidite, and quartzite (all the types which occur 

 on the strike inland) lie in confused, contorted and shattered masses. 

 At the north of the bay the rocks are less disturbed, and dip to the 

 north-west. Black Ordovician (Lower Silurian) shales are faulted 

 down to the north, resting, in a clear coast-section, against the 

 granitoidite. 



Between Llanwenllwyfo and jSTebo the succession is more dis- 

 tinct. Thin-bedded gneiss is seen at several points north-west of 

 Llanwenllwyfo and north of Plas uchaf ; the overlying green schist 

 is well exposed around Bhos manarch ; and the capping grani- 

 toidite, with associated schist-bands, forms the ridge between rTebo 

 and Ty-Newydd, the whole dipping to the north-west. In two 

 quarries south-east of Nebo there is well exposed a strong band of 

 quartzite and quartzose conglomerate, similar to some of the masses 

 on the coast. I have elsewhere* given reasons for believing that 

 this is the equivalent of the quartzose conglomerate of Twt Hill ; 

 and I stated that in these quarries the rock is unconformably over- 

 lain by black shales of (at least) Bala age. If the shales are 

 Tremadoc or Arenig, as Prof. Hughes has since maintained, the fact 

 is still more strongly confirmatory of the Archaean age of the 

 quartzite. As the point is important, I submit a section (figs. 5 & 

 6) from each of these quarries. 



Since this quartz -rock is Precambrian, is conformably underlain 

 and overlain by gneissic strata, and occurs on the coast in the closest 

 association with gneiss and granitoidite, there can be no hesitation 

 in referring it to the older Archaean series. It must not however, 

 be confounded with the quartz-schist of Bodafon Mountain, which is 

 lower in the succession. 



Granitoidite and dark schist are found along the ridge to the 

 west, and at the base of Paris Mountain. I have not examined the 

 latter locality ; but Mr. Allport kindly allows me to use some notes 

 made by him in May 1868. The numbers refer to specimens now 

 in the British Museum. 



"443. Pine-grained granite? South-east flank of Paris Mountain. 



" 444. Granite ? 100 yards from last. 



* Geol. Mag. March 1880, p. 118. 



