Park. — On Granitic Bocks in the King-country. 361 



of frothy purnice and dust, and streams of liquid rhyolitic 

 lava. This display culminated in later Pliocene ages in the 

 formation of the massive mountains Euapehu and Tongariro, 

 the graceful Egmont, the table-topped Horohoro, and the 

 ridge-shaped Tarawera. 



The evidences of volcanic activity in more recent times 

 abound on every hand. We have the numerous basic cones 

 of the x\uckland isthmus, the semi-basic Ngauruhoe, and the 

 acidic tuffs and muds at Tarawera and Eotomahana. 



This record of the igneous eruptions in New Zealand is 

 merely a wide generalisation, but it serves to show that there 

 has been no succession whatever of acidic and basic volcanic 

 products in this area. It could easily be shown that even in 

 recent times both classes have been erupted almost, if not 

 quite, contemporaneously in regions not far separated from 

 each other. It is therefore evident that the theory of the two 

 magmas cannot be applied to New Zealand. 



Another and perhaps more admissible theory is that the 

 liquid lavas and solid products which issue from volcanic vents 

 are erupted from large cavities in the solid crust of the earth 

 filled with molten rocks. These huge cavities are generally sup- 

 posed to exist at no great distance from the surface, and they 

 are believed to have been formed by the contraction of the 

 crust causing irregular crumpling and folding, and consequent 

 entanglement, of portions of the original magma. This 

 hypothesis does not deny the existence of a central liquid 

 magma of a homogeneous character, and it may help us 

 to explain the diversified character of our igneous eruptive 

 rocks. 



The elaborate experiments of Fouque, Delesse, Daubree, 

 and others have shown that all the different kinds of igneous 

 rocks with which we are acquainted could be produced by the 

 fusion of existing aqueous or crystalline rocks. If these cavities 

 do exist, whatever the cause of their origin, it is evident that 

 the highly-heated liquid lavas or rocks with which they are 

 filled would fuse the solid rocks in contact with them, and thus 

 largely determine the character of the fiery mass. Where a 

 number of independent cavities existed the nature of the solid 

 materials erupted from them would vary according to the 

 character of the rocks adjacent to them. Where the deep- 

 seated rocks of a district consisted of slates and limestones the 

 fusion of these would form a basic lava, and where sandstones 

 or granites a highly-acid lava. It is well known that some 

 volcanoes have erupted both acidic and basic lavas at different 

 periods of their history, and this might be explained by the 

 internal molten rock being at one time in contact with acidic 

 rocks ; at another with basic rocks. It would be interesting 

 to discover that the existence of a great formation of granite, 



