Chapter xxxviii

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Professor Judd, collecting the andesitic rocks as a whole (both lavas and sills), has grouped them into amphibole and mica-andesites, and pyroxene-andesites.[221] The thick lumpy and non-persistent sheets of these rocks sometimes found near the centres of protrusion of the gabbros and granophyres are probably sills.

[Footnote 221: _Quart. Journ. Geol. Soc._ vol. xlvi. (1890), p. 356. Professor Judd has there described under the name of "propylites" various members of the volcanic series which he believes to have undergone alteration from solfataric action. I have not been able to discover any trace of such action, but I have found that the lavas of the plateaux assume a peculiar condition where they have been affected by large intrusive masses of granophyre or gabbro. (See _postea_,

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