Vol. 6$.~] INLIER IN THE EASTERN MENDLPS. 231 



reaching a maximum length of 2 millimetres, but generally 

 smaller. Only a few small felspar-phenocrysts are to be seen. 



Under the microscope, the very abundant groundmass is seen to 

 be microlitic, and to be full of minute felspar-needles which show 

 a general parallelism of arrangement and flow-structure round the 

 phenocrysts. There is some peroxide of iron and a good deal of 

 leucoxene in the groundmass. The ferromagnesian phenocrysts 

 clearly include two minerals — augite and a rhombic pyroxene. 

 The augite is perfectly fresh, and shows the normal cleavage, 

 extinction, and brilliant polarization-colours. The rhombic 

 pyroxene is represented by pale, often regularly-idiomorphic 

 pseudomorphs, with straight extinction. They are almost certainly 

 bastite-pseudomorphs after enstatite (see PI. XVIII, fig. 1). They 

 frequently enclose small patches of epidote, and are sometimes 

 intergrown with the augite. The felspars are sometimes so much 

 altered, that all sign of twinning and cleavage has disappeared ; 

 in other sections, however, they are much fresher, and exhibit 

 twinning on the Carlsbad and albite-types, and low extinction- 

 angles with maxima of 10° to 12°, showing them to be probably 

 oligoclase-andesines. Epidote is prominent as an alteration -product. 



Another section, taken from the top of the cliff on the south 

 side of Moon's-Hill Quarry, shows rather abundant epidote, small 

 irregular vesicles filled with a chloritic mineral, and much red 

 oxide of iron aggregated round the vesicles and crystals. Yet 

 another specimen, taken from the small excavation between the 

 two quarries, contains very numerous small vesicles filled with a 

 green chloritic mineral. Eight other sections taken from different 

 parts of the quarry, though varying as regards the extent to which 

 alteration of the phenocrysts has taken place, are all of essentially 

 the same type as the rock already somewhat fully described. 



The specific gravity of the typical Moon's-Hill rock, which was 

 kindly determined by Mr. 0. C. M. Davis, B.Sc, is 2*72. An 

 analysis made by Mr. E. M. Lane in the Chemical Laboratory at 

 University College, Bristol, gave the following result : — 



Per cent. 



Si0 2 62-40 



A1 3 14-80 



Pe* 3 11-20 



Mg<3 512 



Na 2 trace 



38} _!1 8 



Total 100-0 



The most remarkable point about this analysis is the very small 

 amount of soda present. 



The Sunnyhill and Beacon-Hill mass. — The rock imme- 

 diately overlying the tuff in Sunnyhill Quarry is of the same 

 type as that at Moon's Hill, but finer-grained and with much 

 glass so as to be nearly isotropic in polarized light. The pheno- 



