great Coal-field of Shropshire, 203 



in its rise and dip it corresponds with the before-mentioned lime- 

 stone, except that the angle which its strata make with the horizon 

 is very uniformly 8% undergoing no change in this respect as it ap- 

 proaches the Severn. But when it has crossed this river and crops 

 out beneath and to the west of the coal strata at Little Wenlock, it 

 appears elevated at an angle of about 20% and forms a continuous 

 line parallel to the Wrekin as far as the Steeraway-hill, the 

 northern extremity of the range, where the strata are suddenly raised 

 to between 30° and 40°. 



In tracing the outburst of this deposit of limestone it is impossible 

 not to be struck by the uniformity in the line of direction of the 

 whole ridge, at the same time that the elevation of that portion north 

 of the Severn so greatly exceeds the almost horizontal position of the 

 part which lies to the south of that river. A second circumstance 

 peculiar to the elevated portion is its intimate connexion v/ith a 

 green- stone trap of which no traces are to be found in the other part 

 of the range. 



This greenstone is perfectly unstratified, and forms two principal 

 deposits ; the one constituting the chief mass of the hill on which 

 the town of Little Wenlock is built, the other that of Steeraway- 

 hill. 



Of this greenstone there are several varieties. Sometimes it is of 

 a dark bluish-green colour, passing into iron-grey; is massive, glim- 

 mering, of a coarse-grained uneven fracture, and breaks into irregu- 

 lar rather blunt-edged fragments ; it gives a pale greenish-grey streak, 

 is considerably heavy and difficultly frangible. When immersed in 

 an acid an effervescence is perceived from various parts of its surface : 

 by examination with a lens it appears to be composed of hornblende 

 and felspar, with a little calcareous spar and mica. 



In the next variety it is coarser, consisting for the most part of 

 2 c 2 



