Geology in New Zealand

Dominion, Volume 28, Issue 121, 15 February 1935, Page 13

Geology in New Zealand

Sir,— Regarding the statements made bv the writer of a Nature Note in last Saturday’s “Dominion.” let jne mention that the vulcanicity occurring in the North Island of New Zealand in past a'-es was not an effective agent m the placing of the shark’s tooth in the hmeftoiie boulder, as your contributor seems to imply. The vulcanism mentioned did not occur in jurassic times, but was almost entirely confined to pl‘°cene and recent times. The time difference between the jurassic and pliocene times is to be reckoned in hundreds ot millions of years. , It also should be observed that the limestone concerned, despite the fact that it is of late pliocene age, was laid down in regions particularly free from any active volcanic manifestation whatsoever. The limestone was formed from the accumulation on the sea floor of shells, <-rit and wave-broken shell fragments, fitter to be compacted together by mineral cementation processes. It is not inconceivable that the shark on its death should leave its teeth among tlie rubble on this sea floor, when the softer fleshy and cartilaginous material of its mouth had disintegrated away from them (it being remembered that tliu shivk a species of larcharodon, had teeth which did not socket into the jawbone, ns do those of a modern fish, say the schnapper). . . We must not harbour the idea that natural processes and changes such as that effecting the uplift of our limestone-to-be from its bclow-sea position to itpresent one SOO feet above sea level, were in anv wav cataclysmic in nature, we have every reason to believe that the uplift in question was a very gradual one; moreover, we know that it L . ation. Wo need not explain here that the eastern coastline of New Zealand has been affected, and is still being atfeeted, bv outward thrusts from the floor of the Pacific, tending to elevate the eastern margin of New Zealand relative to sea. level. Although in general the. movement is a verv gradual, humanly imperceptible, one. there have been occasions when, as on February 3. 1931. local restricted portions- of the coastline, through the disruption of the rocks under the strain, have risen an appreciable amount m R very short time, and earthquakes have occurred. The movement, however, is usually only a few feet at a time. Ihus. eventually, as a result of this upward movement, onr limestone deposit is raised from out of the sen to SOO ieet or moie above it. , . . . As the centuries rolled by the constant wear and tear of the worlds weather has caused the denudation of this limestone deposit now forming part of the land surface. Much of it is dissolved away, but isolated fragments (they may be as large as a house) we often meet on the hillsides and in the gullies, resting on the stratum which was below the limestone deposit, originally the sea floor on which the limestone accumulated. Such was the boulder which the writer of the Nature Note met with at Arapawaniu. It may interest him and others to know that if he goes some miles inland up into tlie ranges lie will find sea-shells, and thick deposits of enormous oyster shells, 3000 and 4000 feet above sea level. These arrived at their present situation in exactly the same way as the limestone we have been considering. It may seem a stupendous movement, but don t forget perhaps Nature’s greatest weapon-ytime. With this she can achieve the impossible.—l am. etc.. GEOLOGY STUDENT. Napier, February 11.