. The hollow spherulites of the Yellowstone and Great Britain. ithophysce of the American , we have found that felspathic fibres project outwardsinto a quartz-amygdaloid, that parts of some nodules show anopen network of similar fibres now embedded in secondary material,and we have been able to draw a direct analogy with the porousspherulites of the Yellowstone. Finally, traces have been found ofan encrusting mineral curiously resembling tridymite. All thismilitates strongly against an hypothesis of corrosion, so that weneed feel no hesitation in applying to the older spheruli
. The hollow spherulites of the Yellowstone and Great Britain. ithophysce of the American , we have found that felspathic fibres project outwardsinto a quartz-amygdaloid, that parts of some nodules show anopen network of similar fibres now embedded in secondary material,and we have been able to draw a direct analogy with the porousspherulites of the Yellowstone. Finally, traces have been found ofan encrusting mineral curiously resembling tridymite. All thismilitates strongly against an hypothesis of corrosion, so that weneed feel no hesitation in applying to the older spherulites of GreatBritain a conclusion which appears in accord with the facts observedin the rocks of the National Park of the United States. In the case of the large amygdaloids, irregular, partly circular Quart. Journ. Geol. Soc. vol. xlii (1886) p. 185 & pi. ix, fig. 2.•^ Ihid. vol. liv (1898) p. 115 & pi. vii, fig. 1. ^ The brecciation-veins traversing the nodules of Pontesford Hill presentidentical features. Quart. Journ. Geol Soc. Vol. LVII. Pl. VI. Fig.
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