34 Rocks of Noyang. 



The analysis thus calculated assigns '26 Mol. of R 2 3 and 

 1*86 Mol. of RO bases to the hornblende. This may repre- 

 sent the truth so far ; but it is not likely that these con- 

 stituents consist wholly of ferric oxide and lime, but that 

 portions of the alumina and magnesia would be included in 

 the amphibole minerals. 



Assuming, however, that this calculation sufficiently 

 expresses the composition of the rock as it is, and that the 

 kaolin represents the altered felspars, the following may be 

 assigned as the probable percentage composition of the 

 unaltered rock; and in this I have assumed that the unaltered 

 condition of the felspars was that of an oligoclase of the 

 constitution Al. 3 : An. 1.: — 



Oligoclase ... 



Magnesia-iron-mica 



Hornblende ... 



Magnetite ... 



Quartz 



Sphene 



Apatite 



100-30 

 In this rock the ratio of the constituents is — 



Felspar, 1-30 ; Quartz, -42 ; RO Minerals, 1. 



(p.) Quartz-Mica- F 'or •phy 'rites and Qwartz-Granophyrites.* 



-- Rocks of this class are confined to the eastern side of the 

 Tambo River, excepting where, above the Noyang ford, a 

 great offshoot of the main mass extends from near Mount 

 Elizabeth to the westward of the river, and along the course 

 of the Haunted Stream. Many strong dykes of these rocks 

 also extend similarly westward, and it might even be said 

 with truth that they radiate from the great central 

 porphyritic masses of Mount Elizabeth. The relations of 

 these quartz porphyrites and granophyrites to the older 

 crystalline-granular diorites may be well seen in Navigation 

 Creek and the Tambo River. They penetrate the latter 

 either as masses, or as parallel or winding dykes. The 

 crystalline-granular rocks are in many places cut off by the 

 porphyrites, but there are also frequent instances where the 



48-25 



23-49 



11-64 



2-32 



14-01 



•09 



•50 



Spherulitic quartz-porphyrite. 



