348 Transactions. — Geology. 



homogeneous substances, such as ice, by torsion/'' Such sys- 

 tems of fractures may also be readily obtained in glass. Dau- 

 bree obtained systems of fractures crossing one another at 

 angles approaching a right angle. In each system some of 

 the fractures were arranged in a radiating or fan-shaped man- 

 ner, others were parallel to each other. Great caution, of 

 course, is needful in applying such results to the explanation 

 of natural dislocations, for it is uncertain how far we are 

 justified in supposing the earth's crust would behave as a 

 homogeneous mass, and the conditions of the experiment are 

 no doubt very different. Still, the resemblance of the arrange- 

 ment of these natural dislocations to that of the artificial 

 fractures is sufficiently close to lend interest to the compari- 

 son. 



Many instances of transverse dislocations might be cited 

 in the Taupo zone. The line of volcanic mountains at the 

 south end of Lake Taupo may be due to such a fracture. We 

 have here the two mountains Kakaramea (4,266ft.) and Pi- 

 hanga, of about the same height. They are connected by a 

 high ridge of volcanic rock, and the long axis of the group lies 

 at right angles to the line of the Euapehu-Tongariro fissure. 

 Pihanga has a crater showing to the north, and Kakaramea is 

 said to have traces of a crater. The rocks of which they are 

 composed are generally similar to those of Tongariro. Where 

 the slopes of these mountains come down to the south shore of 

 Lake Taupo we find the hot springs and geysers of Tokaanu, 

 as well as various springs at intervals as far as Waihi. 



Bocks of Tongariro. — Specimens of rocks from Ngauruhoe 

 and Euapehu were collected by Mr. Cussen in 1887, and were 

 described by me in the "Transactions" of the Institute.! 

 Since then I have had the opportunity of making very ex- 

 tensive collections of rocks on Tongariro and in its neigh- 

 bourhood, and am able to add to what was then written. I 

 am indebted also to the great kindness of Mr. J. A. Pond, 

 Colonial Analyst, for a valuable and extensive series of 

 analyses of rocks from Tongariro, Ngauruhoe, and Lake 

 Taupo. These furnish an important and welcome supplement 

 to the results obtained by microscopical examination. 



Hochstetter has stated that all the rocks collected by him 

 in the Taupo volcanic zone belonged to the family of acid 

 volcanic rocks known as rhyolites. In the paper referred to 

 it was shown that the intermediate (or slightly basic) group of 

 lavas known as the augite-andesites were largely represented 

 in the district. This result is amply confirmed by Mr. Pond's 



* Daubree, " Etudes Synthetiques de G^ologie Experimentales," 

 tome i., p. 307. 



t "Trans. N.Z. Inst.," vol. xx., p. 306. 



