20 PALEOZOIC TIME. [CHAP. II. 



anticline, though very quartzose, are partially constructed 

 of felsite grains." 



If we next consider the Upper Cambrian we find they 

 also are thickest in Merioneth, being there no less than 

 7,000 feet thick. Near Llanberis, west of Snowdon, the 

 Lingula Flags are only 2,300 feet, and there is little that 

 can be called Tremadoc. Finally, near Bangor, the Lingula 

 Flags are represented by sandstones and muds tones resting 

 on the grits which overlie the basal conglomerate ; even if 

 the basement beds are also part of the same series (see 

 ante, p. 17) the total thickness is not more than 1,000 feet, 

 and there is no representative of the Tremadoc. 



A similar change takes place southward ; near St. Davids 

 the Lingula Flags are not more than 2,000 feet thick, and 

 consist largely of sandstones and flags, many of the beds 

 showing ripple marks, and all attesting shore conditions. 

 The Tremadoc slates are 1,000 feet thick. 



At Malvern there is 500 feet of sandstone resting on 

 Archaean, and overlain by 1,000 feet of shale belonging to 

 the Dolgelly and Tremadoc groups, and in Shropshire there 

 is a similar sequence. In Warwickshire, however, the series 

 again thickens ; there is a massive quartzite of uncertain 

 age, but probably Upper Cambrian, overlain by 2,000 feet 

 of Upper Cambrian shale. 



The Cambrian rocks of Wales seem, therefore, to have 

 been formed in a deep trough between lofty ridges formed 

 of the Archaean rocks on the east and on the west, and 

 possibly also to the south-east. 



The only Irish rocks referable to the Cambrian system are 

 those in Wicklow and Wexf ord. 1 Lithologically they are com- 

 parable to the Lower Cambrian of Wales and Shropshire, 

 but as their base is not seen, we do not know on what they 

 rest, and no definite fossils have yet been found in them. 



1 The Galway rocks, regarded as Cambrian by Mr. Kinahan, are 

 more probably of Archaean age. 



