Vol. 65.] THE ORDOVICIAN AND SILURIAN ROCKS OF CONWAY. 173 



III. Scenery oe the District. 



Everywhere the rocks of the Volcanic Series rise abruptly to 

 form rough mountainous land, the summits of which reach 800 feet 

 or more above sea-level ; these are generally heather- or gorse-clad, 

 though affording a certain amount of rough pasture-land. There 

 is always a rapid fall of ground where the Dicranograjptus-Sh&lea 

 succeed the Ashy Grits, aud it is to this that the steep slope of the 

 eastern end of Conway Mountain is due. The Bodeidda and 

 Deganwy Mudstones, on the other hand, occupy gently rolling 

 ground for the most part, while a decided feature invariably marks 

 the oncoming of the Conway Castle Grits. The Gyffin Shales, like 

 the Dicranorjraptus-fih.ales, are usually found in the hollows ; but 

 the Benarth Flags and Grits give rise to hilly country with an 

 average elevation of about 400 feet due south of Conway, and this 

 land is usually more wooded than any other part of the district. 



IV. Structure oe the District. 



In the main, the beds of the Conway district form part of a great 

 buckled syncline with a south-south-easterly pitch. A series of 

 ' tear-faults ' (Marr), intimately connected with the buckling and 

 resulting from tangential movement, also affect all the beds in the 

 northern part of the area, and the combined effect of the buckling 

 and tear-faulting is well brought out by the outcrop of the Conway 

 Castle Grits. There is a considerable amount of mineralization 

 along some of these tear-faults, and where there is a good 

 rock-face bounding a fault, horizontal slickensiding is sometimes 

 beautifully shown. 



The structure of the south-eastern part of the area seems, how- 

 ever, to be somewhat more complicated ; there appears to be an 

 important line of disturbance running from Gyffin to Hendre, and 

 though from the nature of the ground it is hard to trace it through 

 the Benarth Woods, there seems to be little room for doubt that it 

 is the same line that comes out on the Benarth shore immediately 

 south of the Point. Everywhere above this line of disturbance 

 the beds are packed together far more closely than they are any- 

 where below it ; anticlines and synclines succeed each other very 

 rapidly, and all show a tendency to overfold northwards. 



The apparently simple anticline of Gyffin Shales near Bryn 

 Glorian Mawr is in reality much more crumpled than it has been 

 possible to indicate on the map (PI. VIII) ; the general nature of 

 the folding is, however, well displayed along the Benarth shore (see 

 PI. VIII, section). Here the characteristic features are clearly 

 seen, namely the tendency to overfolding northwards, and the 

 overriding of the upper limb over the lower wherever a fold is 

 broken. It seems, therefore, almost impossible to avoid the con- 

 clusion that the Benarth-Gyffin-Hendre line of disturbance is really 



