Dr. C. Callaway — On the Archcean Rocks. 



351 



this country. In the Malverns, the Archgean ridge is pushed up be- 

 tween a pair of faults, and in no spot do the Cambrian or Silurian 

 rocks clearly rest upon the older series. The structure and relations 

 of the Wrekin in Shropshire are similar. In Caernarvonshire, 

 on Llyn Padarn, near Llanberis, Cambrian conglomerates are in 

 contact with an older group, but the junction appears to be a fault. 

 In Anglesey, the newer Archaean series, the Pebidian, is faulted 

 against both the Cambrian and the gneiss group. 



Nowhere will the student who is fond of faults find a happier 

 hunting-ground than in Anglesey. In a morning's walk, he will 

 probably meet with more dislocations than men. The Geological 

 Survey Map displays a network of earth-fractures, but where the 

 surveyors have put in one, they have sometimes overlooked two. 

 The more attentively and closely the ground is studied, the more 

 frequently do faults appear. 



The difficulty from faulting may often be overcome by the 

 following method. To make the matter clearer, an actual example 

 will be taken. In Central Anglesey there is a band of granitoid 



Fig 1. Section in Central Anglesey, showing proof of the gneissic succession. 



Halleflinta. 



Quartz-schist. 



Limestone. 



d. Grey gneiss. 



e. Green schist. 

 /. Granitoid rock. 



Fl,F2, Fault. 



rock (/), coloured pink on the Survey Map, passing down into a 

 dark-coloured schist (e), which rises up into an anticlinal arch (seen 

 at the west end of the section, Fig. 1), throwing ofi" the granitoid beds 

 on both sides. But in this area we can find no strata below the 

 schist, and when we follow the rocks towards either the west or 

 east, we come to a fault (Fl, F2). However, on searching the ground 

 to the east, we light upon the dark schist, forming a parallel band 

 about two miles from the granitoid zone. Then working along the 

 sea-coast to the west, where the rocks are clearly exposed in the 

 cliffs, we see that the dark beds are underlain by a considerable 

 thickness of grey gneiss {d), under which is a thin band of crystalline 

 limestone (c), followed in succession by quartz-schist Qj), and, at 

 the base of the section, by hJilleflanta (a). This brings us back 

 again to the fault {F2). It might at first sight seem as it" this fault 

 broke the succession, and that it was useless to pursue the inquiry ; 



