282 Reports and Proceedings — 



discovering a peak which he Bamed Mount Clarke, 7256 feet high, 

 and in finding traces of glaciation in the form of roches moutonnees 

 throughout an area of about 100 square miles. The best-preserved 

 of the ice-worn surfaces were found in a valley named by the author 

 the Wilkinson Yalley, running from N.E. to S.W., immediately 

 south of Miiller's Peak and the Abbot Eange. No traces of ice- 

 action were found at less than 5800 feet above the sea. 



The rocks showing ice-action are all granitic, and the fact that 

 the surfaces have been polished by glaciers is said to be proved by 

 the great size of such surfaces, by their occurrence on spurs and 

 projecting points, by many of them being worn down to the same 

 general level, and by their not coinciding in direction with the joints 

 that traverse the rock. 



In conclusion the author briefly compared the evidence of glacial 

 action in Australia with that in New Zealand. 



3. "The Physical Conditions involved in the Injection, Extrusion, 

 and Cooling of Igneous Matter." By H. J. Johnston-Lavis, M.D. 



The great disproportion between the displays of Volcanic activity 

 in the same volcano at different times, and between the eruptions of 

 different volcanoes, is a subject deserving the most attentive con- 

 sideration. The violence of a volcanic outburst does not bear any 

 relation to the quantity of material ejected. The union of water 

 with lavas may be compared with the solution of a gas in water ; 

 but there is reason to believe that in their deep-seated sources lavas 

 contain little or no water. If igneous matter be extruded through 

 dry strata, the eruption might take place without explosive manifesta- 

 tions. But if igneous matter be extruded through watei'-bearing 

 beds, a kind of dialysis would take place between the igneous and 

 aqueous masses. In this way the tension of the steam in the fluid 

 rock may at last become so great that a fissure will be formed at the 

 surface and volcanic action will follow. 



In this way the violence of a volcanic eruption will be determined 

 by the quantity of water contained in the strata through which the 

 lava passes in its passage to the surface, and by the temperature at 

 which it reaches the surface. 



This theory explains the acknowledged sequence of volcanic out- 

 bursts of different degrees of violence, and the intervals which occur 

 between them. It also explains the differences between the central 

 and lateral eruptions of a great volcano, and the phenomena attend- 

 ing its extinction. 



The structures of the igneous rocks, whether of basic or acid com- 

 position, are greatly modified by the presence in them of volatile 

 ingredients. 



The succession of events indicated by the structure of Monte 

 Somma and Vesuvius, Roccamonfina, Monte Vulture and Monte 

 Nuovo, show that after a long cessation of volcanic activity we have 

 an extensive production of fragmentary and scoriaceous material, 

 and that this is gradually succeeded by the eruption of lava-streams. 



The water and other volatile substances, such as sulphates and 

 chlorides, which are given off abundantly in volcanic eruptions, may 

 act as solvents for the various minerals which constituto lavas. 



