president's address — SECTION c. 107 



presumably indicates the presence of an important line of crust- 

 weakness, parallel to the direction of the major features which 

 have guided the po:t-Tertiary orogeny, and along which seismic 

 disturbances still occur, though only occasionally within the area 

 of New. Zealand, as e.g., the Cheviot earthquake O'f 1901 (McKay 

 1902). The great rift of the Tarawera eruption and its extension 

 in Lake Rotoniahana, lies also in the same direction, and parallel 

 to it is perhaps a subsidiary line cf volcanic activitj?- running to the 

 north-east from Mt. Egmont. The main line, however, indicated 

 above is approximately collinear with the westeirn margin of the 

 Tonga Trench, which extends towards Samoa, past the Kermadec 

 Islands and Tonga, the volcanic rocks of which resemble the ande- 

 sites of the North Island of New Zealand, as was pointed out by 

 Speight (1911) and Marshall ('1912). This relationship derives new 

 interest from the recsnt nd highly important seismclogical investi- 

 gation of the crust-movements in the Tonga Trench, carried out 

 by the observai cries at Samoa and Sydney, a statement of which 

 is to be placed before this meeting. We may here welco^me the 

 suggestion urged by Dr. Jagger, of Hawaii, that a vulcanological 

 observatory shcvild be installed in the active regions of New Zea- 

 land, and express the hope that the detailed geological investiga- 

 tion of the past and present volcanic activity will alsO' be taken 

 in hand. 



The Post-Tertiary {Kaikourd) Orogeny. 



The general recognition of the importance of post-Tertiary 

 diastrophism has been a marked feature of the study of the 

 geology in New Zealand during the* past decade. It was clearly 

 recognised by McKay in his later writings {e.g., on the Kaikcuras, 

 1892, and on Central Otago, 1894-7), and was brought to the front 

 again by Park's re-survev of the latter region (1906. 1908, 1909), 

 by Henderson (1911), and by the physiographic studies of Cotton 

 {e.g., 1913, 1916, 1917). The vertical element of the movement is 

 obvious, but a lateral ccmponent is indicated in several regions as 

 mentioned below. This orogeny, however, appears net to have 

 been confined to post-Tertiary time> merelv. but. according to the 

 studios, especially of Henderson (1917, 1920), seems to have been 

 the culmination of a series of much smaller movements whir'h con- 

 tinued soasmodically throughout the Notocene period. To this 

 great orogeny and the consequent denudation is due almost all of 

 the present rebef of New Zealand excepting that of the volcanic 

 mountains. The Kaikoura movements of New Zealand may thus 

 be compared with the Ozarkian movements of America and the 

 Kosciusco movements of Eastern Australia. We must now con- 

 sid-r New Zealand as " a concourse of earth-blocks," which were 

 moved differentially, tilted, war'-ed, or even faulted at this time. 

 The boundaries of the blocks are marked by fault-ccarps in homo- 

 geneous structures, or faulted contacts of older and younger strata, 



