44 



ARCH^AN. 



Caernarvon Bay, including Bardsey Island and the coast from 

 Bardsey Sound to Forth Nevin. 



The Wrekin district of Shropshire. — Some of the older rocks of 

 Shropshire were investigated in 1877 by Mr. S. Allport, who re- 

 garded them as belonging to a volcanic series.^ Dr. C. Callaway 

 subsequently described the Wrekin as a ridge composed of alter- 

 nations of bedded felspathic lavas and tuffs (Pre -Cambrian), flanked 

 on both sides by quartzites (possibly Pre-Cambrian), which are 

 succeeded by the Hollybush Sandstone (Lingula Flags), the Shineton 

 Shales (Tremadoc), and the Hoar Edge Grits (Lower Caradoc). 



Fig. 6, — Section across the Wrekin, in Shropshire. 

 (Dr. C. Callaway.) 



4. Shineton Shales (Tremadoc). 



3. Hollybush Sandstone (Lingula Flag Series). 



2. Quartzite. 



I. Bedded volcanic tuff (Archaean). 



The dotted lines represent faults. 



These strata appear in places to succeed each other in conformable 

 succession ; but it is doubtful if the conformity with the quartzite 

 is real. The Wrekin Volcanic Series (Uriconian or Febidian) has 

 furnished pebbles to the Longmynd Series. (See Fig. 6 and p. 57.) 

 Dr. Callaway has detected " one good specimen of a worm-burrow, 

 apparently Arenicolites,^'' in the quartzite, and this, if Fre-Cambrian, 

 would be the oldest known British fossil.^ He proposes for it the 

 name Arenicolites uriconiensis? Recent discoveries in the INIidland 

 counties, however, tend to show that the age of the quartzite is 

 probably Cambrian. 



Granitoid rock, and gneiss like that of Malvern, have been ob- 

 served at Primrose Hill and Ercal Hill at the southern and northern 

 ends of the Wrekin range. Quartzites are exposed on the south- 

 east flank of Caer Caradoc, near Church Stretton, and at Lawley 



^ Q. J. xxxiii. 449. 



* Q. J. xxxiv. 763 ; XXXV. 649; G. Mag. 1881, p. 348; 18S4, p. 362; 1885, 

 p. 260. 



^ The term Uriconian is derived from the Roman station Uriconiutn, on the site 

 of which stands the village of Wroxeter, S.E. of Shrewsbury. 



