Glaciation of Anglesea. 409 



scale so strikingly moutonnee, and pressing along the 

 slopes of Llanfair-fechan, the lower end of Aber Valley, 

 the seaward flank of Moel Wnion, and across the lower 

 end of the valley of the Ogwen, it marked its track by 

 long, slightly-inclined terraces, somewhat faintly marked, 

 but still clear to the experienced eye when looked for 

 from the shores of Beaumaris. Beyond this the glacier 

 continued its course across Lleyn, and onward to the 

 region now occupied by St. George's Channel. 



Furthermore, in my opinion, so great was the size 

 and power of this ice-flow, that it hindered the glaciers 

 of Y-Foel-fras, Llanberis, and Nant-ffrancon from 

 encroaching on the territory of Anglesea, and they 

 simply joined the larger glacier as minor tributary ice- 

 streams. For this reason it happens that the glacial 

 striations of Anglesea, as we might at first expect, do 

 not point towards the old glacier-valleys of Snowdonia 

 that open on the Straits, but run at right angles to 

 the courses of these comparatively minor glaciers. 



If we now turn to the rocks that form the banks of 

 Menai Straits, we find that they chiefly consist of nearly 

 flat-lying Carboniferous strata, and looking at the dis- 

 position of these beds from Traeth Melyn, opposite 

 Caernarvon, to Llanfair-pwll-gwyngyll, in Anglesea, and 

 on the opposite shore from Caernarvon to Bangor, 

 there is no reason to doubt that from end to end they 

 once filled the whole of the region now occupied by the 

 Straits. The larger part of this region, as it now exists, 

 is of Carboniferous Limestone age; but it by no 

 means consists entirely of solid limestone. On the 

 contrary, numerous bands of shale and friable sandstones 

 and conglomerates are intermingled with the limestones, 

 together with beds of soft red marl. On the coast oppo- 

 site Caernarvon, the low cliffs are entirely formed of 

 red marl overlying the limestone ; and on the Caer- 



