G lactation of Anglesea. 403 



divide the two regions; but Carboniferous rocks form 

 the larger part of either shore, and the Straits may 

 be considered simply as a long shallow valley, the 

 bottom of which happens to lie beneath the level 

 of the sea. The question thus arises At what epoch 

 and by what means was Anglesea separated from the 

 mainland ? 



Looking north-west across the country from any of 

 the minor heights a mile or two inland between Bangor 

 and Caernarvon, no one would even suspect the existence 

 of the Straits. The whole of Anglesea is low ; and only 

 one steep escarpment, a minor one, occurs in the island 

 that of the Old Ked Sandstone overlooking Traeth 

 Dulas, which rises abruptly above the tidal flat of the 

 Traeth to the height of about 250 feet. 



The entire island may, indeed, be looked on as a 

 gently undulating plain, the higher parts of which 

 attain an average elevation of from 200 to 300 feet above 

 the level of the sea ; while most of its principal brooks 

 and small rivers run north-east and south-west, in 

 depressions with gently sloping sides ; and only one in- 

 land valley, with the same trend, is of any marked 

 importance, namely that of Malldraeth Marsh, in which 

 a small coalfield lies. There are, however, a few 

 exceptions to the average levels mentioned above the 

 summit of Holy head mountain being 709 feet, and Grarn, 

 near Llanfairynghornwy, 558 feet above the sea, while 

 the greatest elevation crossed by the sections of the 

 Geological Survey (sheet No. 40) is only about 400 feet 

 high. 



On the opposite side of the Straits, the same kind of 

 low, undulating scenery prevails for several miles inland, 

 with the same kind of minor north-east valleys, one 

 marked instance of which occurs in a long, shallow, and 



D D 2 



