THE ACTIVE VOLCANOES OF NEW ZEALAND 711 



the floor and walls are dotted with hot springs and fumaroles, and 

 around some of these springs a great deal of iron pyrite is being 

 deposited on pebbles, particularly in a spring called "The Frying 

 Pan." The pyrite becomes disseminated in the sinter and to some 

 extent it impregnates the thermally altered rhyolite. It seems to 

 owe its origin to the reaction between H 2 S and some iron salt, which 

 in all probability is the chloride. The sulphide coats the pebbles 

 with a black, smooth, waterworn layer which later tends to assume 

 more nearly the appearance of typical pyrite. Art assay was run 

 on this pyrite deposit to determine the presence or absence of gold, 

 and no trace of gold or silver was found. It seems probable that 

 the pyrite in the sinters around Rotorua is of the same origin, and 

 the large deposits of sulphur around the springs near Lake Rotorua 

 appear to be due to the oxidation in the air of the H 2 S so plentiful 

 in these waters. 



While the great fissure practically ends at the Southern Crater 

 there are some smaller fissures and faults in Earthquake Flats 

 which indicate the extension of the disturbance beyond the main 

 fissure. There are lines of former movement which were again 

 depressed a few feet. 



DETAILED DESCRIPTION OF THE ROCKS OF MOUNT TARAWERA 



This mountain was originally made up of interbedded rhyolite 

 and rhyolite pumice, with streaks of dark gray to black, spherulitic 

 obsidian running through the rhyolite. The bands often have the 

 appearance of irregular dikes in the rhyolite, but they are probably 

 due to the varying rate of cooling in different parts of the flows. 

 The dark obsidian contains many fragments of the lighter rhyolite, 

 and in some cases these have the appearance of being partly 

 absorbed. This may be explained by the rhyolite fracturing on 

 the cooled surface, permitting the liquid beneath to pour out 

 around the brecciated fragments and to cool quickly. Good 

 examples of this spherulitic obsidian were found on the road 

 leading from Te Wairoa down to the landing on Lake Tarawera. 

 Fragments may also be picked up among the debris from 

 Tarawera, showing that the rock exists in the deeper beds in the 

 mountain. 



