V.—Notes on the Ash-Slates and other Rooks of the Lake District

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Abstract
Taking the other and coarser constituents of such slates as are X not wholly made up of the fine “base,”—the constituents which may be spoken of as “porphyritic,”—the lapilli vary very greatly in number and distinctness. In a large part of the roofing-slates they are either no longer discernible at all or are so exceedingly faded and blurred as to be just barely recognizable, often as patches altered to chlorite, or chlorite and calcite, in which the felspar-laths of the original andesitic ground-mass may still be seen comparatively little altered. In cases where there is reason to suppose that the lapilli were largely of more basic nature, this almost complete alteration of them is observed, as might naturally be expected.

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