Hector. — Presidential Address. 468 



oysters of the same species tlirougbout, this limestone must 

 have been deposited in the same depth of water marking the 

 period of the close of the deposit of the great blue papa 

 formation. Since that period this limestone has been inclined 

 by the gradual dome-like upheaval of the central area of the 

 North Island of New Zealand. During this period of upheaval 

 there was no trace whatever of the contemporaneous existence 

 of any of the volcanic rocks that played such an important 

 part in the later history of the district. Thus, it was not until 

 we got on the top of the limestone that we found, near Eua- 

 pehu, on its south side, outliers of conglomerate and gravel, 

 showing water-carried material derived from these volcanic 

 rocks ; but in the opposite direction, towards the Bay of Plenty, 

 and towards the Thames and Waikato Valleys, or any part 

 of the northern half of the dome, we nowhere find any trace of 

 the marine tertiary rocks. If present, they had been completely 

 smothered by subsequent volcanic deposits. In explanation of 

 this, it may be suggested that all the ejected volcanic matter 

 has, in past times, by a prevailing southerly direction of the 

 wind, been carried to the north, and so smothered the country 

 as to completely obscure the tertiary rocks. Be that as it 

 might, what was found was that the southern flank of this 

 dome was composed of marine tertiary rocks, while the northern 

 is a sloping plateau, superficially composed of volcanic detritus. 



Dr. V. Hochstetter, who first examined and gave an account 

 of this district, long ago pointed out that all over this sloping 

 plateau great valleys have been eroded and then filled up again 

 iDy the products of eruptions, cones have been built up by vol- 

 canic matter, and great flows of lava have taken place of an 

 extremely siliceous type, so siliceous that they are barely fusible, 

 along with others which set in a glossy mass called obsidian, 

 or in a vesicular form as pumice stone, which is nothing but 

 glassy lava blown out by steam. 



Now, wherever this kind of lava has been accumulated so as 

 to form great volcanic cones, of which you find many instances 

 at Tauhara, Tarawera, Mount Edgecumbe, Ruapehu itself, there 

 has been sooner or later formed a corresponding depression, 

 simply, as v. Hochstetter pointed out long ago, by the local 

 subsidence of the surface over the vacuity from which some part 

 of the ejected matter had been abstracted; and for long after 

 a mild generation of steam was kept up round the basins 

 enclosing the lakes by the expiring energies of the former 

 great volcanic activity. That applies to every part of the 

 coimtry except Ngauruhoe, where there still remains part of 

 the primitive form of volcanic activity, as evidenced in the 

 ejection of actual masses of lava, which forms on cooling 

 into stony rock. Such was the lava exuded in 1870. With 

 that exception, all volcanic action in this district has always 



