460 Transactions. — Geology. 



of ortlioclase and quartz. The matrix in wliicli they are imbedded is a 

 stnictureless glass, densely crowded with an immense number of veiy minute 

 yellowish brown gi-anules, nearly uniform in size, and quite translucent. 

 Black grains of magnetite are also scattered through the mass. The section 

 cut contains a pale red crystal of irregular form, which exhibits no double 

 refraction — it is evidently garnet. 



Some of the orthoclase contains numerous cavities filled with brown glass, 

 and one of the quartz crystals contains a characteristic rhomboidal cavity with 

 a vacuity and five or six belonites. 



The " fluidal" structure, as it has been called, is remarkably well shown ; 

 streams of microlites and brown glass bend round the larger crystals, and 

 clearly indicate the plastic condition of the mass subsequently to their for- 

 mation. 



No. 353 (Snoioy Peak Range) is a rock of quite similar character. 



Art. LXXY. — Deei^ Sinking in the Lava Beds of Mount Eden. 



By J. C. Firth. 



[Read before the Auckland Institute, 26<7i August, 1874,] 



Early in 1873 I commenced sinking a well in my grounds at Mount Eden, 

 with the view of obtaining a constant supply of water. I w^as led to undertake 

 this work from the circumstance that at various points around the mountain 

 springs of excellent water are met with. The most notable of these is the 

 spring found by Mr. Seccombe, yielding in the driest seasons about 80,000 

 gallons daily of most excellent water. 



I do not know that a record of my explorations will present any features 

 of much interest to the general public. To myself, though unsuccessful in 

 my search for water, they were full of interest, for, as I penetrated each 

 successive lava stream, it seemed like the turning over of the leaves of some 

 ancient and unknown book. I am disposed to believe I have obtained a few 

 facts which may, in the hands of scientific men, be of some little use in 

 heli)ing them to elucidate some of the phenomena which in bygone times have 

 played so great a part in changing the features of the land we live in. The 

 point of commencement was 329 feet above sea level, and 313 feet below the 

 summit of the mountain. The depth to which I penetrated was 212 feet, or 

 within 117 feet of sea level at high water mark, or about thirty feet below the 

 bottom of Mr. Seccombe's well before referred to. 



The accompanying section presents the thickness, position, and details of 

 the successive beds of volcanic ash and lava through which I passed : — 



