GEOLOGY OF THE BTIISTOL COALFIELD. 123 



A still more remarkable proof of this fact may be studied in a 

 field near Charfield railway station, where lifted up on the top of 

 the Trap, and also embedded in it, are fossils themselves unaltered 

 in form. 



The central part of the Greenstone is solid, and formed of 

 Felspar and Hornblende principally, but towards the surface 

 interspersed with veins of Calcite and Quartz. "Unfortunately, 

 the several constituents are so intimately blended together, that 

 no separate crystals can be obtained for crystallographic measure- 

 ment or analysis. In some places the rock resembles Serpentine 

 or Steatite. In others may be found nodules of Chlorite, 

 Prehnite, and Gerlite. Indeed, this is one of the best English 

 localities for Prehnite, and the locality is named in our works on 

 Mineralogy. 



The following are three analyses that have been made of the 

 rocks in this quarry. The first sample was taken in as pure a 

 state as possible from the centre of the quarry. It did not 

 effervesce with an acid. The second was taken when the mass 

 was mixed with inseparable particles of Quartz; and the third 

 where particles of Calcite occurred. 



The altered Llandovery beds before mentioned were next 

 examined, and had a purplish color from iron contained in the 

 original sand. They are more conveniently placed for examination 

 on the western slope of the Greenstone . Their vesicular and 



