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PROLONGATION OF THE AXIS OF THE CARADOC. 



The highly inclined and dislocated position of the beds of sandstone, wherever they 

 approach to these hills, is of itself sufficient geological evidence that the trap has been 

 forced up through these sediments, and where we find these movements accompanied 

 by such remarkable changes of lithological structure we can no longer doubt of their 

 origin 1 . 



Such is the composition of the trap and altered rocks of the Caradoc Ridge. Having 

 remarked that the Caradoc sandstone, extending through Horderley to Aston and Gorton, 

 terminated in a narrow anticlinal on the line of Caer Caradoc, I was induced to search 

 for trap rocks in that direction. The first clear exhibition of them I discovered is at 

 Wartle Knoll, eight miles south-west of Ragleth, the south-western end of the Caradoc. 

 (see Map.) This conical hill is similar to many parts of the Caradoc, consisting 

 chiefly of compact felspar with passages into coarse and ill-defined greenstone. One 

 variety of the felspar rock contains grains of quartz, and another has a conglo- 

 merate or brecciated character. In the hills of Carwood, north-east of this cone, 

 the sandstones are very felspathose, partially altered, and dip away in broken masses 

 from the intruding rock ; and the analogy between the phenomena observable around 

 this little boss and those on the flanks of the Great Caradoc is complete. The south- 

 western termination of the line of disturbance occasioned by the intrusive rocks along 

 this axis is further traceable in several irregular dykes or small protrusions. One of 

 these is on the sides of the Middleway lane, in the deep comb on the western side of 

 Hopesay Common, where highly dislocated strata of sandstone and shale are thrown off 

 a little boss of trap rock of very mixed characters, the mass being penetrated by veins 

 of white calcareous spar, the whole much resembling a mixed calcareous and serpenti- 

 nous rock, which I shall presently describe as occurring on the banks of the Severn near 

 Cound Lodge. It may be remarked, that although it might be difficult to assign any 

 precise age to the sandstone immediately in contact with the intrusive rock of this point, 

 the broken knolls, with the contiguous strata tilted to the west, consist of the Ludlow 



1 The Rev. William Vernon Harcourt has directed his attention to the chemical changes produced in sedi- 

 mentary rocks by the application of long- continued heat. He informs me that in the Yorkshire iron fur- 

 naces, where a variety of millstone grit is employed as the furnace-stone, after having been in long- continued 

 contact with the molten metal, the stone undergoes a peculiar kind of fusion, not of the mass, but of the par- 

 ticles of which it is composed, the disseminated felspar serving as a flux to the siliceous grains : in some instances 

 he has found portions of the stone converted into a mass of felspar regularly crystallized ; in others, veins 

 or nests of various crystals occurring at intervals, the intermediate substance of the stone being comparatively 

 little altered. This circumstance Mr. Harcourt attributes, to the differences in the original texture or ingre- 

 dients of the rock, which have occasioned the heat and volatile matter penetrating the substance of the 

 stone, to produce similar effects in similar parts, however distant the one from the other. He states that the 

 portions of the stone which have borne the strongest heat, have entirely lost the fracture and characters of a 

 sedimentary rock, and assumed a high degree of density and hardness, which becomes greater in proportion to 

 the presence of aluminous, ferruginous, or calcareous matter. Among other analogies, the modern parallel 

 seems to explain how certain portions of sedimentary strata near the igneous rock may be slightly changed, 

 while others more remote may be much altered. 



