MONIAN SYSTEM OP ROCKS. 545 



all the land, transgressing far beyond the limit of the Cambrians, 

 and lying everywhere in Anglesey and the east of Ireland on the 

 Monian. This era is well known to have been one of wide-spread 

 depression, as Arenig rocks form the base of the scries in so many 

 countries. In Anglesey the earliest sea-shore is often seen with 

 the huge fragments forming beach-breccias, such as are found near 

 Holyhead Mountain, the Garn, and at Llanerchymedd, but these are 

 very local ; usually the ancient rocks have been well ground down 

 and turned into quartz-conglomerates, as at Nebo, Pen-bryn-yr- 

 Eglwys, and near Gaerwen, or even into grits, as on the west side of 

 Llyn-faelog, and south of Holland Arms. Though the Monian rocks 

 had now been formed, they were not left in peace. They were pro- 

 bably raised into land before Silurian times, and they formed the 

 margin of the sea in the Devonian, Carboniferous, and Permian 

 Periods. At the time of England's great disquietude, the Monian 

 rocks were cut up and sliced, huge faults were brought about, and 

 the northern district pushed over the Ordovician. In the volcanic 

 districts the rocks gaped asunder and let down small slices into their 

 midst. The result of these movements was to raise the area to land 

 once more ; and so it has remained, to all appearance, ever since, if 

 we except the supposed submergence of the glacial epoch. 



It is not easy to determine the age of the metamorphism of the 

 Monian rocks : stated generally, the earliest moment which theore- 

 tical considerations will permit would suit best with the facts. The 

 materials, in fact, in most cases, seem to be specially suitable for 

 crystallization, and even the upper part contains fragments already 

 crystalline. Much therefore of the metamorphism must have been 

 immediate. 



Such is the history of the Monian rocks, as read by the light of 

 the facts observed, and it is one which impresses itself strongly 

 on the mind of a worker on the ground. Whether we stand on 

 an eminence in Anglesey and look eastward on the long Snowdonian 

 range, towering into the sky, or rest on the slopes of Llanberis and 

 turn our eyes westward over the island plain, the contrast is 

 marvellous. Why are those old rocks plains, and these, more modern, 

 mountains ? The difference dates from an early time. In Anglesey 

 the great volcanos, casting out their ashes and melting the rocks 

 into diorites and granites, have formed a great ge-anticlinal. But 

 beneath the range of Snowdon lie 3000 ft. of Cambrian, which has 

 come from Anglesey and the west. This, then, at least was the 

 height of the mountains formed by Monian rocks, and it was probably 

 much more. This mass has formed a buttress ; the earth-stresses to 

 which it has been subject have riven it to fragments, but have been 

 unable to remove it ; against it the newer rocks have been pressed 

 and they have been turned on end and raised into the air. Thus 

 Mona created Cambria and raised it above herself. 



In return for this, geologists have made the Cambrian system 

 obscure the Monian, and declare it was only an altered representa- 

 tive of the former — the mother the altered representative of the 

 child 1 But this great system of rocks is not metamorphosed Cam- 



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