602 MESSES. S. H. REYNOLDS AND C. I. GARDINER [Nov. 1 896, 



porphyritic constituents are fair-sized plagioclase-felspars and 

 augites. The felspars are very greatly altered, but are generally 

 rimmed with a layer of fresh material ; the augites occur in masses 

 of aggregated crystals, often accompanied by rhombic pyroxene. 



In two rocks from different ends of the hill porphyritic horn- 

 blendes, showing the characteristic cleavage and pleochroism, are 

 to be seen. The crystals are much fretted away, and replaced round 

 their margins by fringes in which one can recognize magnetite and 

 haematite. These marginal fringes occur round all the hornblendes, 

 while here and there patches of similar constitution occur without 

 any central hornblende, though no doubt the patches have been 

 formed from hornblendes in the same way as the fringes. One of 

 these rocks, from the spot marked 80 in the map, has 52*8 per cent, 

 of silica, and its specific gravity is 2*8. This rock is also noticeable 

 for the presence of amygdules of chlorite enclosing beautiful little 

 spherulites of quartz similar to those of Grange Hill (see fig. 5). 



Pig. 5. — Bomblende-andesite [80], Hill of Allen, x about 40. 



m 



The section was drawn in polarized light, and shows a large patch of a 

 chloritic mineral enclosing numerous little spherulites, probably of quartz, 

 all with the characteristic black cross. 



At the northern end of the hill occurs a fine dark-coloured, some- 

 times vesicular, compact basalt, more or less in the line of strike 

 of the last-mentioned rocks. Sections of this rock are remarkable 

 for the large amount of magnetite in the groundmass, and its aggre- 

 gation round some of the vesicles and felspars in a way sometimes 

 recalling the appearance of micropegmatite. The felspars are much 

 altered, and give a low extinction-angle. The augites form large 

 plates, and are sometimes very fresh, sometimes much altered. 



