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Continuance is rather a quality of all thrombi, and is essentially growth, whether by lamellation or agglomeration.

Growth is by substitution at the proximal end and by subperiosteal lamellation circumferentially.

The upper half of the drawing is occupied by a crystal of plagioclastic felspar showing twin lamellation and faint zonal markings, and with numerous irregular dark-brown inclosures of glass, probably containing magnetite dust and matter similar to that of the groundmass of the rock which consists of felspar microliths, granules of olivine, and augite crystals, grains of magnetite, and apparently a little interstitial glass.

In the lower ranges of the hills, gigantic portions of gneiss rise conspicuously, so detached from the original chain and so rounded by the action of the atmosphere, aided by their concentric lamellation, that but for their prodigious dimensions, they might be regarded as boulders.