406 PEOE. P. MAESHALL ON THE [Aug. 1906, 



amount of alumina is correspondingly reduced. This must be 

 due to the considerable quantity of magnetite that is present. The 

 high percentage of lime in B is accounted for by the presence of 

 melanite and nosean. 



A plutonic inclusion occurs in several places in this leucitophyre 

 (A). Slices show that it is composed almost solely of a glassy felspar 

 (apparently orthoclase) and segirine, the latter in small quantity. 

 No nepheline or leu cite were found in any of the slices. 



The leucitophyre occurs only at Puketeraki, so far as known at 

 present. In hand-specimens it differs but little from the ordinary 

 trachytoid phonolites, and the leucite is but poorly developed. 

 Prom surface-indications, the rock would appear to cover a con- 

 siderable area near Seacliff, but this inference has not yet been 

 confirmed by microscopical or chemical work. 



The rock rests upon a melilite-basalt, which in turn overlies 

 calcareous sandstone. The trachytoid phonolite forms the upper- 

 most rock-formation of this part of the district. 



13. Trachydolerites. — Dense dark-green or black rocks, in 

 which crystals of olivine and nepheline can be distinguished. 

 I have given a full description of these rocks elsewhere. In slices, 

 olivine and brown augite are seen to occur in small grains, singly 

 or in groups. In all cases they are surrounded by a mantle 

 of segirine and magnetite. Crystals of sodalite sometimes 

 5 millimetres long, but usually much smaller, are often present. 

 Eesorbed crystals of amphibole are often numerous (Mount Cargill) 

 and sometimes a brown unchanged core remains. The ground- 

 mass has aegirine and cossyrite as coloured constituents. The 

 latter always has a ' spongy ' structure. Its pleochroism is intense, 

 from pale greenish-brown to dark coffee-brown ; but the absence of 

 crystallographic outlines interferes with a determination of the 

 pleochroic values of the different crystallographic directions. Some- 

 times there is a trachytoid, sometimes — though rarely — a nepheli- 

 nitoid (southern slopes of Flagstaff) structure in the groundmass, 

 which consists of varying proportions of these constituents. A little 

 apatite is present. The rock varies but slightly throughout the 

 10 square miles of its extent. 



An included fragment of a plutonic rock, found on the southern 

 slopes of Flagstaff, was given to me by Mr. T. Menzies. It consists 

 of sodalite, felspar (orthoclase), nepheline, a little cossyrite, and 

 magnetite. The rock is hypidiomorphic. The pleochroism of the 

 cossyrite is a light-green, b black, c dark-brown. Extinction-angle 

 on 010, 43°. There is no olivine or brown augite. 



I have previously given an account of the chemical relationship 

 of this rock in the ' Transactions ' of the Australasian Association 

 for the Advancement of Science, vol. x, 1904 (Dunedin) p. 186. 



