326 Transactions. — Geology. 



The age of our coal presents a marked distinction from that 

 of the great coal-deposits of England, continental Europe, and 

 North America, which occur in strata lying between the Old 

 and New Ked Sandstones. In the early part of this century 

 so imbued were geologists with the idea that true coals were 

 confined to this horizon that the coal-bearing strata received 

 the age-name " Carboniferous," which is now generally applied 

 to all rocks of this period, whether they contain carbonaceous 

 deposits or not. 



The subsequent discoveries of true coal in Lower Second- 

 ary strata in New South Wales, in Jurassic strata in India, 

 and Upper Secondary strata in New Zealand, conclusively 

 showed that, given the necessary geological conditions, coal 

 could be formed at any period of the earth's history. Up to 

 the present time no coal-seams have been found in rocks 

 below the Devonian, and from this circumstance it is argued 

 by some scientists that there must have been a scarcity of 

 carbonic acid on the earth's surface prior to this period — too 

 little, in fact, to favour the growth of great forests or dense 

 vegetation of any kind. However true this may be of the Old 

 "World, it certainly does not apply to New Zealand. Among 

 the Silurian schists and marbles of Western Otago, which are 

 simply altered sandstones and limestones, there occur layers 

 and nests of graphite under conditions which leave little room 

 for doubt that they are the product of altered carbonaceous 

 matter of vegetable origin. 



It is now generally admitted that all coals rest on old soils 

 or land-surfaces, and consist of nothing but vegetable matter. 

 Judging from the leaf-impressions in the coal-shales, it is pro- 

 bable that our coals are principally the result of forest-vegeta- 

 tion of long-continued growth, among which dicotyledons are 

 largely represented, and after these cycads, conifers, and 

 ferns. 



With one or two exceptions, the coal -deposits of this 

 country occur near the base of the measures, which generally 

 rest on the basement-rock of the district, showing that the 

 forests grew on a long-persistent aiid comparatively stationary 

 surface, with perhaps in most cases a tendency to a downward 

 movement. After a period of rest, during which the car- 

 bonaceous matter accumulated, the land began to sink, and 

 from the character of the estuarine and marine strata which 

 cover the coal it can be ascertained that these old forests 

 flourished on low-lying areas contiguous to the sea, or in deep 

 estuaries or bays to which the sea had free access. The 

 marginal or littoral character of our coal-areas can be seen at 

 a glance by looking at the mineral map of New Zealand 

 issued with the Geological Eepoi'ts for 1886-87. 



As a result of our coals having been formed on old laud- 



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