PLTJTOKIC EOCKS OF GAEABA-L HILL AND MEALL BEE AC. 115 



Iron ores. 



Olivine. 



Pyroxene. 



Hornblende. 



Biotite. 



Plagioclase. 



Orthoclase, microcline, and quartz. 



These minerals are not all present in any one rock, but by piecing 

 together the evidence furnished by different rocks we can establish 

 the general order for the entire group. 



Now it will be seen at once that there is a striking resemblance 

 between the order in which the minerals commence to form, and 

 their general distribution in the different kinds of rock. This fact 

 will be referred to again after the chemical composition of the rocks 

 has been described. 



So far we have been referring to the essential minerals. The 

 accessory minerals, sphene, apatite, and zircon, are absent from the 

 ultra-basic rocks, but they occur in the other members of the group. 

 They are often idiomorphic, and they are present as inclusions in 

 the other minerals with which they are associated. If we regard 

 the whole area as the result of the consolidation of a large plutonic 

 reservoir, this would indicate that, although they are the first to form 

 in a magma having the composition of the rocks in which they 

 occur, they were not the first to form in the original magma. 



4. Chemical Composition. 



Owing to the great kindness of Mr. Player, we are able to give a 

 cries of analyses of typical specimens. 



I. II. III. ly. V. VI. VII. 



SiOg 38-6 46-0 47-5 62-6 62-3 66-6 75-8 



AI2O3 3-7 6-8 15-6 17-7 186 17*4 13-7 



Cr^Og 1 -2 -1 



FeA 7-6 3-0 26 J-2 1-5 1-1 -5 



FeO 7-8 7-5 7-1 33 30 2-1 -3 



CaO 7-7 8-1 9-8 4-6 4-3 2-2 -5 



MgO 27-7 23-9 11-7 3-4 2-5 1-2 trace 



Na,0 -8 1-4 2-5 1-9 3-1 1-9 



Kfi -2 -9 1-5 3-7 4-8 4-6 6-5 



Loss on ignition 6-4 2-4 2-4 -7 "6 '9 -3 



99-8 99-6 99-7 997 99*5 99-2 99-5 



Sp. Gr 3-00 3-15 2-96 2-76 2-67 2-62 2-59 



I. (5). OUvine-diallage rock; partly serpentinized. North-east of Loch 

 Garabal. 

 II. (7). Enstatite-diallage-hornblende-biotite-olivine rock. Loose block. 

 North-east of Loch. Garabal. 

 III. (12). Biotite-diorite. W. side of Ben Damhain. 

 IV. (18). Hornblende-granitite. South-west of Ben Damhain. 

 V. (20). Hornblende-granitite. Hill south of AUt-na-Lairige ; near junction 



with porphyritic granitite. 

 VI. (21). Porphyritic granitite. Same locality. 

 VII, (25). Eurite. Vein in hornblende-granitite or tonalite. South-west side 

 of Ben Damhain. 



