Academy of Sciences] 

 No. 1] 



AUSTRALASIA. 



41 



The discussion of the geology of New Caledonia 

 given by Suess (IV) based on the work of (Pelatan '91) ; 

 Glasser ('03), Deprat and Piroutet ('05), and their pred- 

 ecessors, must now be greatly modified as a result of 

 Piroutet's masterly account of the island ('17). The fol- 

 lowing is a brief summary of this most interesting work. 

 (See fig. 12.) The most ancient rocks are a series of 

 mica-, amphibole-, and glaucophane-schists and gneisses, 

 which are followed by gradual passage into sericite-schists 

 and unfossiliferous phyllites, to which an Algonkian or 

 early Paleozoic age is assigned. These were strongly 

 folded along a northwest-southeast axis and eroded before 

 the transgression across them of Permian and Triassic 

 seas, passing from the northeast to the southwest, with a 

 regressive period in the Middle Triassic, but subsequent 

 transgression of the Upper Triassic in the same direction. 

 Rhyolitic eruptions occurred during Lower Triassic times; 

 trachytic, andesitic, and diabasic in Upper Triassic. 

 Folding then occurred along lines slightly oblique to the 

 earlier folding, and the land to the west was again sub- 

 merged at the close of Jurassic times. A succession of 

 transgressions from the southwest to the northeast depos- 

 ited a series of marine and coal-bearing strata alternating 

 with one another, there being also extensive eruptions of 

 rhyolitic and andesitic lavas and tuffs in Neocomian time. 

 By the Senonian period the whole land was submerged, 

 but orogeny followed, again along a direction approxi- 

 mately northwest and southeast as before, but slightly 

 oblique to the older folds. A further marine transgression 

 occurred in Middle Eocene times, again passing from the 

 southwest toward the northeast, with such evidence of 

 minor regressions and breaks as to show the instability of 

 the crust at this period. Andesitic and diabasic eruptions 

 took place. A profound orogeny followed, the direction 

 of the folding being only very slightly oblique to the 

 preceding movements. The dominant overthrusting force 

 came from the northeast, causing the overturning to the 

 southwest, of the majority of the folds, especially those 

 along the west coast, which are sometimes broken, and 

 piled up into a series of overthrust flakes, with reversal 

 of the normal order of superposition. Owing to the in- 

 equality in the distribution of the folding force along the 

 line of strike, and the uneven resistance of the ancient 

 folded subcrustal masses, arcuate folds open to the north 

 occur in the northeastern part of the island, while the 

 existence in a zone along the east coast of a series of 

 folds overturned in a northeasterly direction, may be due 

 to the foundering of crust-blocks in that region, of which 

 there is other evidence. It was during this Tertiary 

 period of intense crust-folding that the huge masses of 

 ultrabasic rocks were injected, which occupy, according 

 to the map reproduced herewith, an area of approxi- 

 mately 2,600 square miles out of a total area for the whole 

 island of 6,450 square miles. Piroutet has clearly shown 



