518 EEV. J. r. BLAKE ON THE 



ashes, and marked with browner patches, as if it were sporadically 

 dolomitized. And then in the headland of Pen-y-parc we get 

 another agglomerate of quartz-lumps and ash, as in fig. 20. 



Fig. 20. — View of Pen-y-jparc, Cemmaes, looking east. 



1. Quartz. 2. Unstratified ash. 



Similar phenomena are seen along the coast all the way to Cem- 

 maes, sometimes with irregular curling masses of limestone, and 

 sometimes with similar ones of quartz. 



On the east side of Cemmaes matters are on a larger scale. 

 Pirst we have the great limestone-quarries of Trwyn-y-parc, in 

 which there are two bands of tolerably pure limestone, separated by 

 a narrow band of calcareous shale. There does not seem to be a 

 trace of any organism in it, and it is entirely crystalline in structure. 

 It is here, no doubt, in the form of a lenticular bed. On the north 

 side of this we again reach a district which is cut up by trough- 

 faults like that around Penbryn yr Eglwys — the very reverse of the 

 state of things on the east of Amlwch. Fortunately the Ordovician 

 shales are black, and can be easily recognized. One of these slices 

 we find in Forth Eadric, in the midst of irregular ashy rocks. 

 Beyond this comes a quartz-knob, forming the promontory 

 Trwyn-y-baurth ; it is, as usual, isolated, and the ashes are 

 in no way altered in appearance by its presence, but are soft 

 and easily decayed. Moreover, the phenomena here are those of 

 ordinary faulting, resulting, not from pressure, but from tension. 

 "We cannot get this quartz-knob into its place by folding. 



The coast at Llanbadrig church is one of the most remarkable and 

 instructive spots in the island. The groundwork is ashy, as before, 

 and some of the ashes are calcareous and show structural planes ; 

 amongst these intrude (there is no other word to use) the masses 

 of crystalline limestone which run out into the headlands. In this 

 there is no stratification and no constancy of direction, and it runs 

 across the lines of the ashes, or carries portions of them along with 

 it. It is occasionally dolomitic, and the whole is intruded on by some 

 parallel narrow dykes. The most remarkable feature, however, in 

 the limestone is the oolitic character of some parts. The interior of 

 the grains is not organic, but consists of finely crystalline mosaic 

 limestone, like fragments of the limestone itself and like the matrix 

 in which the grains are imbedded ; such fragments are surrounded 



