CAVES ON RANGITOTO.
Sir, —It swms the general occurrence in lava flows for there to be caves, or more properly speaking, fissures. These fissures are caused, I venture to gay, by contraction of the lava at time of cooling. The natural tendency of direction for the stone to fissure is towards the apex or vent from which it flowed, the fissures on every occa sion happening posterior to every other ;ic tivity, except disintegration. If it were possible for a lava stream to out channels, such as described, in solid rocks, such channels would necessarily be blocked up with tho lava; or even if they were not, the sides of the fissures would bo so altered by the consequent heat as to at least be different from other parts of the rock which remained comparatively cool. There is but one theory permissible, apart from contraction, and that is earthquake, but as we know that all matter contracts in cooling, this is prdbably tho cause of fissures in lava beds, and wo must expect to find such in all flows of any magnitude. The more compact the stone is<ytho moi'i! pronounced will the fissure be.—J.A.
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New Zealand Herald, Volume XLIX, Issue 14929, 29 February 1912, Page 4
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194CAVES ON RANGITOTO. New Zealand Herald, Volume XLIX, Issue 14929, 29 February 1912, Page 4
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