ERUPTION OF THE CARADOC POSTERIOR TO THE LUDLOW ROCKS. 231 



steepest acclivities of the chief hill, and close to the house of Botvyle, is a knoll about 

 five hundred paces in length and two hundred in breadth, of impure limestone belong- 

 ing to the middle portion of the Ludlow rocks. The strata are vertical, or dip 80° to 

 the south, and strike in one part due east and west, in another 10° and 15° north and 

 south of those points, their direction conforming to a buttress of the trap of Caer Ca- 

 radoc, which advances towards Botvyle. (See Map.) Some of these beds are concre- 

 tionary, others consist of thick, flaglike, impure grey limestone, containing fossils of 

 the Aymestry or middle Ludlow rock, among which are Terebratula Wilsoni, Pleuro- 

 toma corallii, Atrypa affinis, &c. The limestone is for the most part much indurated 

 and altered, and although it has been burnt for lime, it is now little used, the adjoining 

 limestone of the coal measures at Le Botwood being of superior quality (see p. 93, 

 etseq.). 



Other strata, representing the Lower Ludlow rocks, and containing the Asaphus cau- 

 datus, are broken off from this insulated mass of limestone, and ranging nearly at a 

 right angle to its direction, strike to the south-west, along the flank of the chain, occu- 

 pying the low hills of Caradoc Coppice and New Farm. These Lower Ludlow beds, 

 though exceedingly dislocated, are not like the limestone changed, being further from 

 the intrusive rock. The altered mass standing on its edges, in an insulated position, 

 amid rocks of much higher antiquity than itself, and adhering to the sides of an eruptive 

 ridge, shows that the Ludlow formation was at one period continuously spread over 

 this district, and that the Botvyle outlier is its only remnant, the underlying formations 

 having been upheaved, and the overlying denuded. (See PI. 31. f. 4.) No portion of 

 the highly convulsed region laid down upon the annexed map offers so striking an ex- 

 ample of the extent of the disturbing forces as this insulated mass of Ludlow rock ; dis- 

 severed from similar deposits by an interval of five miles and encased in a gorge between 

 two mountain masses ; one a volcanic rock which has thrown the Upper Silurian beds 

 into mural position, the other slaty rocks of the Cambrian System (the Longmynd). 

 The latter, indeed, is also penetrated by numberless intruders of trap, which we shall 

 presently consider. In the meantime, the phenomena at Botvyle prove, that the trap 

 forming the main ridge of the Caradoc has been evolved posterior to the consolidation 

 of the Silurian System. 



This period of elevation was synchronous with that which threw up the Silurian 

 strata on the flanks of the Wrekin, and was antecedent to and distinct from those 

 eruptions which on lines more or less parallel, subsequently affected the carboniferous 

 system, as will be shown in the following pages. 



2 f 2 



