544 W. TV. WATTS OlS THE IG5?"E0TJS AISTD 



alteration-product. There are often two generations of felspar, 

 larger lath-shaped porphyritic crystals and small microliths ; both 

 appear to be labradorite, though they are a good deal decomposed 

 into greyish granular products : occasionally there are inclusions of 

 serpentine in the felspar. 



The Pyroxene is of two kinds. Colourless augite with marked 

 cleavage- and growth-lines, often twinned, occurs in large and small 

 irregular grains polarizing with bright colours and giving the usual 

 high extinction-angle of augite ; it fits in betw^een the other consti- 

 tuents. Grains of rhombic pyroxene are also present in great 

 quantity, though generally much decomposed ; it is green, fibrous, 

 and dichroic, changing from fuU green to light straw-yellow, and 

 with one marked cleavage, so that it is the mineral that charac- 

 terizes the andesites, namely, enstatite. It is altered generally into 

 brownish fibrous matter, and still further into a mass of serpentine. 

 The enstatite is present in much greater quantity than the augite. 



Many scattered grains and crystals of magnetite and ilmenite are 

 present, having evidently consolidated first, followed by the felspar, 

 and that by pyroxenes, of which the enstatite probably solidified 

 earlier than the augite. A highly altered form of this type presents 

 the same characters, while the augite remains unaltered ; the serpen- 

 tinous products in shape and structure suggest the form of enstatite 

 rather than that of olivine ; opacite occupies the spaces between the 

 crystals. A good deal of calcite is present in some of them, in- 

 vading the serpentine first and then the felspar. 



The average sp. gr, of the rock is 2-7. It must be called an ensta- 

 tite- diabase or dolerite. 



(6) HiUs J^. and S. of the Chapel in Bausley village. This is the 

 dark-grey variety showing large distinctly twinned felspars and 

 obvious pyroxene. It looks much like the Whin-Sill diabase, but the 

 resemblance disap^oears under the microscope, which also reveals that 

 a greater change has taken place in the rock than would be suspected. 

 The structure of the rock is generally ophitic, the two principal 

 ingredients being closely crystallized together ; but occasionally there 

 are felspar microliths or opacite between the crystals. There is an 

 unusually large proportion of jolagioclase in large crystals, but the 

 pyroxene is almost unrecognizable ; I think, however, I make out a 

 little augite, and there are the usual serpentinous replacements which 

 suggest the presence of enstatite, though often the grains are edged 

 with calcite. The serpentine fibres are arranged in little radiating 

 groups, and opaque whitish stuff often occurs between the crystals, 

 probably an alteration-product. The sp. gr. of this rock is 2-697. 



(c) A variety appears in Brimford Wood, apparently in segregation- 

 veins, which is rather different from the other types. The structure 

 is ophitic, large crystals of three minerals having formed together. 

 The felspar is much decomposed, but is evidently plagioclase, the 

 augite in large clear colourless crystals, and there is a serpentinous 

 mineral in great quantity which might be a replacement of olivine 

 or enstatite, but Prof. Bonney, who has seen the slide, thinks proba- 

 bly the former, and mentions rocks from Worth Wales rather like 



