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REV. A. W. ROWE OX THE 



radiating from centres ; the spherulites are more apparent in the 

 very microcrystalline portion. But no. 17 is an entirely different 

 rock, of a pinkish-white appearance and not close-grained : the 

 section of this rock reveals a remarkable perlitic structure, the small 

 narrow bands being apparently composed of minute grains of quartz ; 

 the section also contains several circular aggregates of clear felspar. 

 I have been informed that devitrified rhyolites of this character are 

 stated to have been found in Sweden, at Elvedalen, in Hedemarken. 



Quaftz-trtichytes. — The only specimen that I have found of these 

 rocks is cumbered 18 ; the texture of the rock is fine-grained and 

 compact, though vesicular in places ; the section shows that the 

 ground-mass is really vitreous, though so filled with minute grains 

 of quartz as to give it an appearance of a finely granitic character ; 

 it contains some larger crystals of quartz and orthoclase with 

 abundant enclosures and bubbles. 



Felspar-porpliy rites. — These rocks are exceedingly abundant in 

 the drift : the specimens are numbered from 19 to 38. They 

 vary very much in appearance, but in all of them the porphyritic 

 felspar can be clearly seen in the hand-specimens, though none of 

 the crystals are of any great size ; the sections show generally a 

 crypto-crystalline felsitic base, enclosing porphyritic crystals of 

 orthoclase and piagioclase, but chiefly plagioclase — in some cases 

 perfectly clear and transparent, in others in various stages of decom- 

 position, much cracked and with outlines broken and indistinct ; in 

 some sections the felspar is altered into a mealy appearance, in others 

 it has a pearly lustre. Augite is occasionally present in granular 

 aggregates or in scattered crystals, and in some cases quartz. Some 

 fine instances of zonal structure in felspar occur, notably in no. 21, 

 and some sections contain tourmaline in abundance, especially nos. 

 22 to 32 ; this last-mentioned specimen is in many respects worthy 

 of notice, and it is questionable whether it ought not really to be 

 included among the quartz-tourmaline rocks. The hand-specimen 

 is of a dark grey colour and ver} T vesicular, the cavities being 

 lined with minute pyramidal crystals of quartz and with minute 

 crystals of tourmaline. In the section the porphyritic felspar 

 seems to be made up of aggregates of minute crystalline grains 

 corresponding with the ground-mass. The quartz is abundant, 

 chiefly in aggregates ; but one long and very clear crystal shows 

 twinning under crossed nicols, one half remaining dark shot-grey, 

 the other pale yellow ; on rotation both extinguish partially and 

 simultaneously ; when the nicols are not crossed, the pale yellow 

 part on rotation shows dark purplish blue changing to pale yellow, 

 but the other half shows no colour at all. Nos. 33 and 34 are typical 

 augite-andesites ; in both the base is very vitreous and in 34 it shows 

 great disturbance and fluxion-structure very clearly. The plagioclase 

 is very clear, though much broken, and there are some good examples 

 of zonal structure. The augite in 34 is, in most cases, either enclosed 

 within the felspar, so that only a border of felspar is visible, or else 

 attached to it, in some cases lying partly within the felspar, partly 

 in the base ; in 33 there are some good examples of a distinctly 



