130 Transactions. 



large masses, and the inference is they occur as dykes. The 

 fact that some of the gabbros are theralites, and carry nephe- 

 line, points to the possible association of the already described 

 hypabyssal types of rock with a gabbro-magma rather than 

 with a syenitic one. 



In the Te Kinga railway quarry, near the Rotomanu Station, 

 one of the very few excavations made in the Tuhua rocks, 

 in a face some two chains in length, two decomposed dykes 

 are exposed, in addition to a mass of soft basic rock which 

 never came to the surface, the exposed upper portion of which 

 is surrounded by a halo of contact metamorphism from 2 ft. 

 to 3 ft. in thickness separating it from the overlying granites. 

 Sections made from this intrusion are described under No. 55, 

 but the specimens collected were not fresh enough to enable 

 a complete description to be written. In the " No. 1 Bulletin " 

 of the New Zealand Geological Survey, Dr. Bell says, " The top 

 of the Hohuna Range and its southern slopes are seamed in 

 places with narrow basic dykes." The northern slopes above 

 the bush-line have not been examined lithologically, but shep- 

 herds who have traversed this precipitous country say that 

 black seams — probably basic dykes — are frequent in the granites. 

 From the evidence in the Te Kinga quarry and on the Hohuna 

 Range itjwould seem that in places erosion has removed so much 

 of the granite that only a shell now covers a basic igneous rock. 



The specification of the questionably plutonic representatives 

 of the*series is, — 



119. Theralite. In the gabbro-diabases it is impossible to 

 determine the presence of nepheline with certainty by optical 

 means, and micro-chemical tests only revealed its presence in one 

 rock. Half a gramme of the powdered rock was dissolved in 

 dilute HC1, and the solution slowly evaporated in a beaker. 

 Before dryness was reached water was added, and evaporation 

 continued to remove excess of chlorine. When saturation was 

 nearly reached, evaporation was finished on glass slides, with 

 the result that quantities of crystals of sodium-chloride were 

 deposited. Staining only revealed the presence of a mineral 

 which, on the application of hydrochloric acid, formed gela- 

 tinous silica. The presence of nepheline thus determined places 

 the rock in the family of the little-known theralites. It consists 

 of large twinned crystals of schillerised ;egerine. with good 

 <•rvst.allogra.phic outlines, a basic plagioclase, a lirown hornblende, 

 and a little nepheline in panidiomorphic relations, together 

 with a small quantity of interstitial allotriomorphic augite con- 

 verted into serpentine. A few cubes and grains of magnetite 

 are present. The feldspar is labradorite. and appears both in 

 columnar crystals ami as rectangular plates with zonary banding. 



