1853.] RAMSAY — LOWER PAL/EOZOICS OF N. WALES. 169 



of the Alps. We can find no beginning to the existing order of 

 physical phsenomena. 



To the west of the intruded porphyry that ranges from Llanllyfni 

 to St. Ann's Chapel, near the Penrhyn quarries, a fault, that runs 

 from Aber to Dinlle, again throws in the Lingula beds and probably 

 the lower part of the Bala series. The down-throw varies in amount 

 from 2000 to 6000 feet*. East and south of Bangor the greenish 

 sandstones and green and purple slates again crop out from beneath 

 the Lingula shale. They are much altered by the intrusion of an 

 igneous rock which runs from Bangor to Caernarvon. It is composed 

 of quartz and felspar, sometimes well crystallized. Such rocks have 

 been sometimes termed " Granitella." By the addition of mica this 

 rock at Caernarvon would become a perfect granite. This rock is also 

 cut off by a dovracast fault on the north-west, by means of which the 

 Carboniferous Limestone and part of the Coal-Measures abut on the 

 trap. A conglomerate forms part of these Carboniferous rocks, 

 seemingly formed from the waste of the traps and palaeozoic rocks of 

 the neighbourhood. Some of the pebbles are much altered. Such 

 metamorphism as the older palaeozoic rocks had undergone took 

 place, therefore, before the Carboniferous period. The base of the 

 Lingula shales, which at Bangor lies on altered chloritic green and 

 purple sandstones and slates, strikes across the Menai Straits, a little 

 west of Beaumaris, where they lie on chloritic schists and sandstones 

 still more metamorphosed. It is believed that all the rocks of An- 

 glesea coloured light pink on the Survey Maps belong to the same 

 series as the Barmouth and Harlech grits, and the Llanberis and 

 Penrhyn green and purple sandstones and slates, but, the rocks being 

 generally much metamorphosed, the colouring on the map is changed 

 to express such an alteration. At Bangor the same beds graduate 

 by alteration into rocks of the Anglesea type, and the typical Cam- 

 brian colour is shaded on the map into that which expresses Meta- 

 morphic Cambrian. The dark blue shales and grey sandstones and 

 conglomerates of Anglesea, coloured pink on the map, represent Lin- 

 gula beds and part of the Bala or Llandeilo rocks. Near Amlwch 

 two masses of granite are intruded among them, and the strata sur- 

 rounding them have been changed into mica-schist and gneiss. A 

 patch of Old Red Sandstone on the coast opposite Yuys-dulas rests 

 uncouformably on these altered rocks. It has heen formed by their 

 waste and by that of the intruded granite. The date of the metamor- 

 phism was therefore prior to the deposition of the Old Red Sandstone, 

 and the country had also at that time been already much denuded to 

 admit of an originally deep-seated granite being exposed to the wasting 

 action of water at the surface. The metamorphic rocks on the north- 

 west side of the great Caernarvonshire promontory are believed to be 

 the equivalents of the same species of rocks in Anglesea, and of the 

 Barmouth and Harlech grits, &c. The strike of the latter beds near 

 Clynnog-fawr would lead to the inference that the Porth-dinlleyu 

 metamorphic beds are the equivalents of the Llanllyfni purple slates, 

 and of the highly altered sandstones of Glynllifon. Half-way between 

 * See Geological Survey Maps, 78 S.E. & S.W. 



