42 BASIC AND ULTRABASIC IGNEOUS ROCKS— BENSON. [MEMO " ts L voL T, xix, 



that Glasser's conception of these rocks as part of a vast overthrust sheet is inadmissible. 

 The peridotites have metamorphosed the adjacent sediments, often Eocene, and contain many 

 large inclusions of them. The boundaries of the intrusions are sometimes vertical or inclined 

 parallel to the dip of the invaded sediments. "Each of the massifs send out prolongations, 

 almost always parallel to the strike of the beds. Besides these, numerous little intrusions in 

 general elongated in bands in the same direction are excessively frequent, and are encountered 

 almost everywhere." (Op. cit., p. 283 trans.) Other plutonic rocks occur in negligible amount; 

 a few rolled pebbles of granite have been found, and a single dike of the same rock in the schist. 

 Micropegmatite and diorite are equally rare, but a small massif of gabbro is known. 



In New Zealand there was a long period of sedimentation, extending from later Paleozoic 

 up into early Cretaceous times, the youngest sediments of the series having been shown to be 

 Neocomian in age (Arber '17). Some authorities, and most recently Park ('21), have held that 

 an important orogeny with plutonic intrusions interrupted this long period of subsidence and 

 sedimentation about the close of Paleozoic times, and there seems reason to believe that minor 

 breaks occur in the older Mesozoic sequence of beds. Some conglomerates and limestones occur 

 in the series, but by far the greater portion consists of greywackes more or less argillaceous in 

 character, and in Jurassic times especially interbedded with zones containing plant^fossils or 

 even coal. Igneous rocks are rare. Melaphyres and basic breccias occur in the lower portions 

 at Nelson (Marshall '11), and are more widespread intercalated in the Upper Triassic strata. 

 Folding occurred directly following the deposit of the Neocomian beds (it had perhaps com- 

 menced before then), and was felt with varying intensity over the whole region, producing highly 

 compressed strata, overturned folds, and perhaps over widely extending regions metamorphic 

 □chists were formed. The ranges so produced were soon mantled with marine sediments, the 

 first of which have been shown to be of Lower Utatur age, equivalent approximately to the 

 Albian or Middle Cretaceous (Woods '17). There followed Upper Cretaceous (Senonian) and 

 Tertiary sedimentation, the continuity of which, or separation into several series by minor crust- 

 movements, is still a matter under investigation. It would seem, however, that a definite break 

 separated the Senonian from the Middle Tertiary deposits in the northern part of the North 

 Island. Extensive orogenic movements, however, occurred again toward the close of the 

 Tertiary period, resulting both in block-faulting (the Kaikoura movements of Cotton) 

 and the overthrusting of Tertiary deposits by Mesozoic rocks or schists, as exhibited at Nelson 

 (Marshall '11) and on Lake Wakatipu (Park '09) . 3 



The following brief descriptions will indicate the nature of the known occurrences of basi< 

 and ultrabasic rocks in New Zealand. In the extreme north there exists a complex of basic anc 

 ultrabasic rocks the relations of which to each other and to rocks of known age are not cleai 

 (Bell '09). Marshall ('07) has shown the existence of masses of olivine-norite at Ahipara a short 

 distance to the south. Bartrum thinks this may be considered to be coeval with a group of 

 epidiorites intrusive into the Trias-Jura greywackes of the Whangerei district, and, tentatively, 

 that they were erupted during the Cretaceous orogeny. Perhaps, however, they should be 

 grouped with a series of small intrusions of serpentine occurring between here and Aukland, 

 namely near Wade (where troctolite also is present), Warkworth, Wainui, and Kaipara Flats, 

 which invade the probably Senonian "hydraulic limestone," but are apparently older than the 

 Oligocene- Miocene sediments and limestone. This hydraulic limestone is considerably dis- 

 located and broken, but is not very greatly folded. It thus seems probable that the Tertiary 

 crust-movements, which were so marked in New Caledonia, affected to a lesser degree the 

 northwestern peninsula of New Zealand, and were there accompanied by a small amount of 

 intrusion of peridotite, etc. 4 There is a small occurrence of serpentine on the Mokau River also, 

 about 120 miles south of Aukland. This Henderson ('23) found to occupy a fault-plane, but 

 its relation to the adjacent Tertiary limestone is obscure. Specimens from this mass, and from 

 that of Warkworth, prove to be normal harzbergite-serpentine. In the South Island the most 



» For further details reference may be made to the writer's recent summary of the geology of New Zealand (Benson '21). 

 « For the above information the writer is indebted to a private communication from Mr. J. A. Bartrum. 



