58 STRATIGRAPHICAL GEOLOGY 



of similar rocks forms the upland district of Charnwood Forest in 

 Leicestershire. 



The " Charnian Series " has been described by Messrs. Bonney 

 and E. Hill, 26 and more recently by Professor Watts, 27 from whose 

 memoirs the following account is taken. The exposures (partly 

 concealed by Trias) extend over an area about 8 miles long by 5 in 

 breadth, and the strike of the rocks is from north-west to south- 

 east, the general structure being that of a broad anticline broken by 

 faults and flexures. The apparent thickness of the beds exposed, as 

 estimated from a section drawn by Professor Watts, is about 3500 

 feet, but neither base nor top is seen. 



The oldest rocks (Blackbrook Beds) are hard greenish slates and 

 hornstones, which seem originally to have consisted largely of 

 volcanic dust ; with these are some fine gritty beds containing 

 visible quartz-grains, but they are nevertheless hard flinty rocks. 

 The overlying (Maplewell) group consists of coarse volcanic 



(W.30 N. 



WL, TS MS 2 



Fig. 8. SECTION ACROSS THE HEREFORDSHIRE BEACON. 



By Professor T. T. Groom (Quart. Journ. Geol. Soe. Ivi. p. 141). 



Tr.=Trias. Malv. = Malvernian. P.F.=Faults. 



LL to MS2=Silurian Rocks. Ur. =Uriconian. 



breccias and grits with tufts and ashes, some of the latter being of 

 such fine grain that they form hornstones and slates, either green 

 or purple in colour. 



The highest group (Brand Beds) has a conglomerate at the base 

 which contains rounded pebbles of felsite, quartz, quartzite, and 

 slate ; this passes up into brown and purple quartzites with some 

 interstratified sandy shales, in which what seem to be worm-casts 

 have been found. These beds are succeeded by green and purple 

 slates (Swithland slates). 



In the north-west corner of the area, forming Bardon Hill and 

 Peldar Tor, there are irregular masses of a porphyritic andesite and 

 dacite, associated with coarse agglomerates. These seem to indicate 

 the site or proximity of a volcanic vent. In the southern part of 

 the area there are large intrusive masses of augite-syenite, and on 

 the east is the hornblendic granite of Mount Sorrel, a rock which 

 is largely quarried for road-metal. 



Devon and Cornwall. The only other exposures of Archaean 

 rocks in England are the two small areas of the Bolt and Start 



