321 



Granitic rocks occur in the Malvern Hills in association with 



diorites. They have not, however, as yet been described in detail. 



I. II. III. IV. 



Si0 2 ... 76-8 ... 74-6 75'2 ... 75'2 



TiO 2 ... -4 ... none ... '2 ... -2 



A1A ... 13-4 ... 14-2 ... 13-0 ... 13-7 



Fe,0 3 ... -6 ... 1-2 ... -7 ... 1-8 



FeO ... I ... tr. ... -4 ... -6 



CaO ... tr. ... , -4 ... -4 ... -4 



MgO ... tr. ... "3 ... -3 ... -3 



K.,0 ... 6-2 ... 4-9 ... 71 ... 4-0 



Na a O ... 2-2 ... 3-7 ... 1-9 ... 2-6 



H,6 -5 -8 -7 -9 



100-2 1001 99-9 99-2 



Sp. Gr. 2-575 2-601 2'594 2-604 



I. Red granitic rock. Ercal Hill. 

 II. Quartz -felspar rock. North Hill, Malvern. 



III. Quartz-felspar rook. Malvern. Coarse granitic texture. 



IV. Quartz -felspar rock. Malvern. Fine-grained. 



These analyses are all by Mr. PLAYER/ 1 ) 



The granites of Leicestershire have been described by Messrs. HILL 

 and BoNNEY.(2) The dominant rock in the great quarry at Mount 

 Sorrel is a pink biotite-granite (granitite). The striated felspar in this 

 rock is frequently zoned. The quartz is often idiomorphic with respect 

 to the unstriated felspar. Epidote, pyrite, barium sulphate, copper 

 carbonate and molybdenite occur associated with the granite in nests 

 and veins. Contemporaneous veins of pink felsite have been observed 

 in the Mount Sorrel mass. Dr. SORBY (3) has described the microscopic 

 structure of the Mount Sorrel rock and of the glass which resulted 

 from the cooling of portions artificially fused. Mr. MARSHALL who 

 conducted the experiments succeeded in melting in some cases over a 

 ton of the rock. The glass formed by rapid cooling showed under the 

 microscope radial concretions of black oxide of iron surrounded by 

 clear spaces in a dark glass. Other portions showed a fern-like or 

 dendritic arrangement of the oxide. The more slowly-cooled masses 

 showed glassy and stony parts. In fusing the masses it was observed 

 that the ferro-magnesian constituents melted first and that the quartz 

 and felspar tended to rise to a certain extent. This last observation is 

 of great interest inasmuch as it shows that a cooling mass of molten 

 rock may become differentiated into basic and acid portions. 



Hornblende does not play an important part in the Mount Sorrel 

 granite but it occurs more abundantly in the rock exposed in Brazil 



(1) British Assoc. Report, 188(3. 



(2) Q.J.G.S., Vol. XXXIV. (1878), p. 218. 



(3) Proc. Geol. and Poly. Soc., W. Yorks. Vol. IV., p.301, 1863, 



