382 Transactions. — Geology. 



everywhere marks the advent of the Tertiary period and the 

 kixuriant flora of the present time. In the forests of om- coal 

 period there flourished two species of the kauri, which at that 

 time grew all over New Zealand ; three species of the beech, 

 so commonly and erroneously known throughout the colony 

 by the settlers' name of " birch ; " also the oak, laurel, myrtle, 

 heaths, palms, ferns, grasses, &c. 



It is now recognised by geologists that coal could form at 

 any period of the earth's history if the necessary conditions ex- 

 isted, and it is probable that these conditions have continued 

 the same through all geological time. They were — (1) a humid, 

 temperate chmate, favouring the growth of a dense vegetation ; 

 (2) flat or gently-sloping low-lying areas, favourable for the 

 accumulation of thick deposits of vegetable humus and peaty 

 matter ; and (3) a stationary, or nearly stationary, state of the 

 land, to permit a long-continued and uninterrupted growth of 

 vegetation. 



In New Zealand our coal-areas are mostly littoral, of small 

 extent, and patchy, characteristics resultmg princii^ally from the 

 insular and mountainous nature of the country in older Tertiary 

 times. Where the sides of the valleys were steep and the 

 hills met the sea it was impossible for the remains of vegeta- 

 tion to accumulate to any extent ; and this explains the some- 

 what anomalous fact that the coal-measures do not always 

 contain coal. The steej^ness of the land during the coal period 

 is also accountable for the noticeable fact that our coals often 

 thin out towards the dip, and, when lying near the old rocky 

 floor, are usually found to conform with the contours of its 

 surface. 



But whether the forests which formed the coal grew in soils 

 lying directly on the old basement rock, as we find is the case 

 with those of the Auckland Provincial District, or on the upper 

 surface of areas reclaimed from the sea, as is the case of the 

 forests which formed the Shag Point and West Coast coals of 

 the South Island, it happened that after a long period of rest, 

 permitting the accumulation of thick deposits of vegetation, the 

 land began to sink slowly, and in course of time the vegeta- 

 tion became covered by fluviatile clays and sands, generally 

 containing fragments of leaves and other plant-remains derived 

 from the vegetation which continued to flourish on the higher 

 portion of the dry land which had not become submerged. 



As the land continued to sink the fluviatile or estuarine 

 beds became covered by blue clays and greenish-coloured 

 sands, containing the imbedded remains of the numerous 

 Mollusca, crustaceans, corals, whales, sharks, and other life 

 W'hich teemed in the seas of those times. In a few instances 

 in the north of Auckland coalfields true marine beds contain- 

 ing a varied molluscous life appear close to the roof or upper 



