Bartrum. — The Conglomerate at Albany. 429 



2. The basement rocks* of the North Island consist of shales and 

 greywackes which are largely unfossiliferous and therefore of uncertain 

 age, though in part mid-Mesozoic (Marshall, 1911, p. 20). These rocks 

 were subjected to compression in the later Mesozoic which locally was 

 moderately intense, but caused no noteworthy metamorphism in the North 

 Island area. In the Whangaroa district, it is true, schistosity is locally 

 developed in altered igneous rocks associated with the basement strata of 

 that district (Bell and Clarke, 1909, p. 44), though it is still by no means 

 certain that folding movements earlier than the late Mesozoic may not 

 have affected them. In the South Island metamorphism is very general 

 in the members of the oldermass associated with rocks lithologically similar 

 to those of the basement rocks of the north, but it is probable that this 

 metamorphism long antedated the late Mesozoic orogenic movements 

 (Morgan and Bartrum, 1915, pp. 67-71).t 



Plutonic intrusions are r&re in the North Island, but such as there are 

 perhaps synchronize with the vastly greater ones of the west coast of the 

 South Island. Fraser and Adams (1907) assign a pre-Jurassic age to the 

 Moehau intrusion of Coromandel Peninsula, whilst Marshall inclines to 

 the belief that the olivine-norite at Ahipara, in North Auckland, underlies 

 the Mesozoic (" Maitai ") beds of that district — an important conclusion— 

 and considers the schillerization of the augite of the norite evidence of 

 intense pressure. It is necessary to add that it is obvious from his paper 

 that Marshall (1908) believes that this pressure was associated with the 

 late Mesozoic orogenic movements. In the South Island some at least 

 of the granite and other batholithic intrusions, if not Palaeozoic, wefe 

 certainly very early Mesozoic in age, for pebbles of granite and other 

 plutonic types are found in a conglomerate near Nelson (Marshall, 1904). 



Having regard, then, to the probable early date of the plutonic intru- 

 sions of the North Island, and to the lack of noteworthy metamorphism 

 throughout the sediments of the oldermass, there is surely justification 

 for more than a suspicion that the gneissic constituents of the con- 

 glomerates already mentioned are vestiges of a land area which antedated 

 the period of deposition of the Mesozoic (" Maitai ") sediments, and which 

 suffered in turn folding and severe erosion so that intrusive batholiths 

 were uncovered and caused to protrude. Support is afforded this idea 

 by the presence of dioritic material in Jurassic shales in Coromandel 

 Peninsula (Fraser and Adams, 1907), of granitic pebbles in Jurassic sand- 

 stones at Kawhia (McKay, 1884), and of a foliated granite in a con- 

 glomerate in the " Maitai " rocks of the Hautotara Mountains of south- 

 east Wellington (Sollas and McKay, 1906, p. 185) ; but it must be admitted 

 that these plutonic rocks have not been found in the lowest rocks of the 

 sequence either at Coromandel or Kawhia, whilst they are absent from 

 many other known conglomerate bands in the basement rocks. Much 

 can be argued both for and against this view that the writer is inclined 

 to favour with regard to the significance of the gneissic boulders, but one 

 cannot ignore the possibility that these rocks disclose a glimpse of the 

 early geological history of the North Island of which we are ignorant. 

 In the present state of our knowledge it is impossible to come to any 

 conclusions as to the exact date of the abysmal injections, beyond that 



* The "oldermass" of Cotton (Cotton, 1916). 



t Mr. Morgan favours an Aorere age (Ordovician) for several great rock-iinits in 

 Westland and south-west Nelson usually grouped in the Maitai system of early to mid- 

 Mesozoic age. 



