218 Dr. C. Callaway — On Plagioclinal Mountains. 



the same direction. These, taken in order from E. to W., are the 

 Clee Hills, Wenlock Edge, the minor ridges of Chatwall and 

 Hoar Edge, the Wrekin and Caer Caradoc chain, the Longmynd, and 

 the Stiper Stones. Most of these elevations form parts of a great 

 broken S.W. anticlinal, of which the Caer Caradoc and Wrekin 

 chain is the axis. The escarpments to the E. of the axis face, of 

 course, to the N.W. ; the escarpments to the W. of the axis break 

 down to the S.E. All the ridges follow the ordinary rule, except 

 the Wrekin and Caer Caradoc chain, to which attention is specially 

 directed. 



This chain is nearly 30 miles in length, and is broken by three 

 broad gaps of from 4 to 8 miles in breadth. The chief elevations, 

 taken from the N.E., are Lilleshall Hill, the Wrekin range, Caer 

 Caradoc range, and Wartle Knoll. The last, being of inconspicuous 

 elevation and of doubtful structure, may be neglected. The other 

 three agree in displaying the same peculiarity of structure. The 

 beds of which they are composed strike across the axis. 



Lilleshall Hill is one mile in length by one-sixth of a mile in 

 breadth at the base. Its trend is S.S.W. The beds of volcanic ash 

 of which it is composed strike W.S.W. The difference between the 

 geographical and the geological strike is about 45°. 



The Wrelcin chain, consisting of four elevations, the Ercal, 

 Lawrence Hill, the Wrekin, and Primrose Hill, is three miles in 

 length by half a mile in its greatest breadth. It consists of alter- 

 nations of lavas and tuffs dipping to the N., the ridge trending to 

 the S.W. In this case also the divergence of the two strikes is 

 about 45°. An inconspicuous elevation, lying two miles W. of the 

 Wrekin, named Charlton Hill, ranges due N. and S. In this ridge 

 is a band of conglomerate striking E. and W., the divergence of 

 strike amounting to a right angle. 



The Caer Caradoc chain is about six miles long by about half a 

 mile in its greatest breadth. Its chief summits are the Lawley, 

 Caer Caradoc, and the Eagleth. Its strike is to the S.W. The 

 average strike of the grits, tuffs, and felstones which make up the 

 chief part of the range is E. and W. ; intrusions of greenstone 

 sometimes twisting round the strike 20° to 30°, and, on the S.E. 

 side of the Eagleth, causing it to coincide with the trend of the 

 ridge. These disturbances are only local, the usual E. and W. 

 strike being resumed at a distance from the disruptive masses. A 

 great spur which springs from the S.E. side of the range, and juts 

 out for two miles to the E., is composed of beds of grit, breccia, and 

 felstone, which strike in the same direction as the spur. 



It is clear that, with local exceptions, the bedded rocks of the 

 Wrekin and Caer Caradoc chain strike across the axis at angles 

 varying between 45° and 90°. 



It would be evident, a. priori, that such a mountain range could 

 not be formed on the normal plan. The geographical strike bears 

 no causal relation to the original earth- waves. It has been deter- 

 mined not by axes of upheaval, but by parallel faulting. 



A great S.W. line of dislocation commences near Lilleshall Hill 



