120 A. C. KAMSAY ON THE ISLAND OP ANGLESEY. 



limestone ; and on the Caernarvonshire coast for three miles north 

 of the town, also overlying the limestone, there are soft shales of 

 the Coal-measures, sometimes red and marly, and containing thin 

 seams of coal. 



In Anglesey, from three to four miles north-west of the Straits, 

 lies the valley of Malldraeth Marsh, the rocks of which also consist 

 of Carboniferous Limestone, Millstone grit, soft Coal-measure shales, 

 with a little sandstone, beds of coal, and Permian strata ; and this 

 valley, nine miles in length, runs almost exactly parallel to the valley 

 of the Menai Straits. Many years ago, at its north-eastern end, 

 I saw deep glacial striations on the Millstone Grit, running straight 

 down the shallow valley towards Caernarvon Bay. 



Considering that the south-westerly trend of each of these valleys 

 (and of others of minor note) corresponds with the general direction 

 of the glacial striations of Anglesey, and therefore with the onward 

 course of the great glacier that produced them, I have been led to the 

 conclusion that both of the shallow valleys were scooped out in com- 

 paratively soft rocks by the grinding power of the vast glacier coming 

 from the north-east, and that when in the course of time the 

 climate ameliorated and the glacier disappeared the sea flowed in 

 where part of the glacier had been, and Anglesey first became an 

 island, the islets in the narrower and shallower part of the Straits 

 at the Menai and tubular bridges being merely weathered roches 

 moutonnees, once overridden by the moving glacier. 



Malldraeth Marsh, as its name (the sodden sands) implies, is for 

 the most part deeply buried under watery moss and alluvium ; the 

 river that traverses it is artificially banked and tidal for miles from 

 its mouth ; and if the alluvium that covers its surface, and the blown 

 sands at its mouth were removed, it would again become, as it was 

 in old times, an arm of the sea, a kind of low-banked fjord (like the 

 Menai Straits), about nine miles in length, but, unlike the Straits, 

 closed at its north-east end. Nowhere in the Straits is the water 

 more than from 6 to 10 fathoms deep at high water ; and around the 

 islets near the bridges it varies from 3 to 7 fathoms. An elevation 

 of the country of only 42 feet, would in time, by silting up and sub- 

 sequent accumulation of alluvium, turn the north-eastern and south- 

 western parts of the Straits on either side of the islets into valleys 

 like that of Malldraeth Marsh. 



There are some details connected with the partial submergence of 

 North Wales during part of the Glacial epoch which it is needless 

 to enter on with respect to this special subject. Anglesey was, after 

 emergence, apparently joined to Caernarvonshire by an undulating 

 plain of Boulder-clay ; but by and by, through marine waste and 

 subaerial drainage, this material was so much worn away that only 

 the relics of it now remain in occasional cliffs and low banks on 

 either side of the Straits. Then it was that at length Anglesey 

 fairly became an island such as it now appears, though the long 

 channel through which the waters of the Straits flow was ground 

 out at a comparatively early part of the Glacial epoch. 



Such I believe to have been the physical history of Anglesey 



