CHAPTER XIX. 



SILURIAN SYSTEM (continued). 



Trap and altered Rocks of the Caradoc, Wrekin, ^c— Periods of Volcanic Erup- 

 tion. — Dislocations and Outliers of Silurian Rocks. 



"W^E now proceed to consider the structure of the principal ridges of rocks of vol- 

 canic origin which appear in connection with the Lower Silurian Rocks in the country 

 above described. 



Caer Caradoc. 



The bold, narrow, and sharp ridge called the Caradoc is about seven and a half miles 

 in length, tapering at the extremities, and never exceeding half a mile in breadth. The 

 culminating point, or the Caer Caradoc, is 1200 feet above the sea, but the Ragleath or 

 south-western termination does not exceed 1000 feet, and the Lawley or north-eastern 

 900 feet. Several of the intervening and smaller hills do not attain to such elevations. 

 The ridge has a large buttress on its south-western flank, constituting the hills of Hope 

 Bowdler and Cardington, which nearly rival in height the Caer Caradoc and are upwards 

 of a mile in breadth. 



The Caradoc Hills are chiefly composed of different varieties of imbedded or amor- 

 phous trap, the most characteristic specimens of which may be collected from the 

 rugged bosses which protrude through the verdant slopes or rise to their summits, con- 

 tributing to embellish their picturesque forms. (See the opposite sketch.) The rock fre- 

 quently appears through the grass in long dykes, from ten to fifteen feet wide, which 

 meeting in the culminating points of the hills give them a radiated appearance. Their 

 structure is also to be studied in the transverse combs and hollows which separate one 

 hill from another, in broken chasms upon their sides and in the beds of small water- 

 courses which descend from them. The predominant unstratified rock is pink, hard, 

 compact, felspar, breaking into irregular rhombic forms, a clear fresh fracture being ob- 

 tained with difficulty. From this compact felspar there are passages into, and alterna- 

 tions with, so many varieties of syenite and greenstone, that it is impossible to separate 



