§ 15. THE WREKIN. 775 



• The Wrekin is an elliptical hill, about a mile and a 

 quarter long, its highest summit being 1,320 feet above the 

 level of the sea. It is composed of igneous rocks, having 

 on its flanks various members of the Silurian and Carbon- 

 iferous systems, as shown in the section, Lign. 175. The 

 sedimentary deposits within the influence of the erupted 

 volcanic rocks have undergone considerable alteration ; the 

 sandstone being changed into granular quartz rock, much of 

 which is pure white quartz, with particles of decomposed 

 felspar : in some places this rock becomes a brecciated 

 aggregate. 



These igneous masses are various modifications of pink 

 and deep red syenite, consisting of compact felspar with 

 white quartz, and disseminated chlorite : in some parts the 

 mass is made up of felspar with green earth and veins of 

 carbonate of lime. To the south-east of the Wrekin, bosses 

 of a basaltic green-stone, of irregular shape, appear around 

 the village of Little Wenlock {Lign, 175). 



The invaluable work to which I am indebted for most of 

 the interesting facts thus briefly noticed, should be referred 

 to for full details of the geological structure and relations of 

 the deposits under review. The eminent author considers 

 this district of Shropshire as affording unequivocal evidence 

 of the alternate activity and repose of volcanic action, during 

 very long periods in the palaeozoic ages ; and that the fol- 

 lowing sequence of geological events is clearly established : 

 — 1, that volcanic grits were formed during the deposition 

 of the Lower Silurian strata : — 2, the Upper Silurian rocks 

 and Devonian sandstone were accumulated tranquilly, with- 

 out a trace of contemporaneous eruptions : — 3, after their 

 consolidation, the last-mentioned deposits were dismem- 

 bered, and set upon their edges by vast outbursts of 

 intrusive trap : — 4, the Carboniferous system was deposited 

 after the older strata were upheaved: and 5, that sub- 

 sequent dislocations, including some of the most violent 



