Vol. 70.] I, .WAS AT 5TOETH HEAD, OTAGO HABJBOUB. -107 



For the purpose of the present paper it would have been better 

 to describe the kaiwekite simply as a soda-trachyte. 



Mr. J. F. X. Gbeen observed that there was some danger in 

 generalizing from a single section of lava-flows of unknown extent. 

 He enquired whether there was proof 'that the bands of scoria 

 referred to were really intercalated beds, and not merely surface 

 flow-breccias. 



Mr. P. P. Mexnell said that on points like the succession of 

 eruptions too much information could hardly be amassed. It 

 was doubtful, however, whether it threw much light on the 

 constitution of the magmas that had existed down below, for 

 lavas seemed rather to be in the nature of a scum which was 

 -trained off and forced to the surface. Quite apart from hypo- 

 thetical considerations, it was interesting to note that the section 

 described by the Author, like so many others from the so-called 

 ' provinces ' of alkaline rocks, showed numerous non-alkaline Hows. 

 It was not sufficiently recognized that, in even the most richly 

 .alkaline regions, rocks containing felspathoids were the exception 

 rather than the ride ; but petrographers were generally too anxious 

 ■ to devote their attention to the rare and curious to take much 

 account of the more normal types. He was inclined to agree with 

 what Dr. Evans had said regarding nomenclature : the multipli- 

 cation of names was to be deprecated, and it did not seem at all 

 desirable to have those that denoted rare varieties put on a level 

 with such comprehensive terms as basalt. 



Dr. J. V. Elsdex said that the Author had evidently made good 

 use of an excellent opportunity of studying an extended sequence 

 of eruptive phenomena ; but these lavas represented only one phase 

 of the vulcanicity, and it seemed somewhat remarkable that no 

 indications of intrusive dykes appeared to exist in this area. With 

 regard to the process of differentiation assumed by the Author, this 

 necessarily involved the origination of these several Hows in the 

 same magma tic basin. Although such an origin seemed to be 

 highly probable, he would like to examine more closely the evidence 

 upon which this fundamental conclusion was based, as well as the 

 chemical differences of the various rock-types described by the 

 Author, and considered by him to be derivatives of a parent essexite- 

 magma. For this purpose it was necessary to know, not only how 

 far certain molecules were missing (in comparing, for example, the 

 felspar with the felspathoid types), but also how far these had merely 

 entered into different molecular arrangements. The Author had 

 brought forward a large mass of valuable information, and the 

 Fellows were to be congratulated upon having this important paper 

 submitted for their consideration. 



Dr. A. H. Cox remarked on the interest of the paper, which 

 dealt with a district offering yet another example of the well- 

 known tendency for volcanic phases of igneous activity to begin 

 with the emission of lavas mainly basaltic in type. He considered 

 that the coining of a new name for a particular rock often made 



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