22 Rocks of Noyang. 



these rocks might be classed as the analogies of the " micro- 

 granitites." To the south-east the quartz-mica- diorites ter- 

 minate at well-marked examples of crystalline and schistose 

 hornfels in respect of which they are intrusive. 



The quartz-mica-diorite is much decomposed over a large 

 tract of country, which is worn into rounded ridges and 

 rather flat gullies. Elsewhere it stands out in torlike masses, 

 and is well seen in the river course where the excessive floods 

 in the last fifteen years have laid it bare in innumerable 

 places. In its fresh condition it is a hard and somewhat 

 tough rock of a light colour. 



I now proceed to the results of the microscopic and 

 chemical examination of these rocks. 



The sample which I selected as typical occurs at the cross- 

 ing of the Tambo River at Noyang. The structure of the 

 rock is wholly crystalline-granular, and the constituent 

 minerals have been formed in the order in which I now 

 describe them : — 



1. Magnetite in rectangular crystals. It occurs mostly in 

 the mica and amphibole crystals, and more rarely adjoining 

 them. 



2. Magnesia-Iron-Mica (Haughtonite) . This mica occurs 

 in very irregularly-bounded crystals or groups of crystals. 

 The outlines, whether seen in sections parallel or perpendi- 

 cular to the basal cleavage, are most irregular, often running 

 out into narrow protuberances or retreating into deep 

 hollows. In places portions are detached, being either 

 parts of cleavage plates separated from but still accordant 

 with the main mass, or else in other cases broken up 

 into numerous small flakes and scattered at random in 

 the adjoining spaces filled by quartz. The other constituent 

 minerals, amphibole, felspar, and quartz, conform themselves 

 to the outlines of this mica, and the first is associated with 

 it, not merely adjoining, but occasionally more or less 

 enveloped by it. 



At first sight it seemed to me that, in places, the felspar 

 crystals were partially surrounded by the mica as a later 

 production ; but further examination has satisfied me that 

 this is only apparently the case, and arises through the mica 

 crystals having in some cases been partially broken, and in 

 others from the felspar crystal either having crystallised in 

 a pre-existing hollow, or having become fitted partly into 

 it during the movements of the magma before it cooled. 



This mica becomes translucent in shades of brown, and is 



