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Updated: May 1, 2025
The geological formation of the range was slate, traversed by veins of quartz, its interstices being filled with magnesian limestone. Steep precipices and broken rugged gullies alternated on either side of this creek, and in its bed there were large slabs of beautiful slate. The precipices shewed the lateral formation with the rock split into the finest laminae, terminating in sharp points.
In several places I was particularly struck with the fact, that the fine laminae of the clay-slate, where cutting straight through the bands of stratification, and therefore indisputably true cleavage-planes, differed slightly in their greyish and greenish tints of colour, in compactness, and in some of the laminae having a rather more jaspery appearance than others.
Instead of consisting of these thin laminae, gneiss is sometimes simply divided into thick beds, in which the mica has only a slight degree of parallelism to the planes of stratification.
The porphyritic gneiss, or gneiss- granite as it has been called by Humboldt, is only so far foliated that the constituent minerals are arranged with a certain degree of regularity, and may be said to have a "GRAIN," but they are not separated into distinct folia or laminae.
The S.S.W. dip was occasionally succeeded abruptly by a N.N.E. dip, and this by a vertical cleavage, or again by the S.S.W. dip; as in a lofty cliff on the eastern end of the island the laminae of slate were seen to be folded into very large steep curves, ranging in the usual W.N.W. line, I suspect that the varying and opposite dips may possibly be accounted for by the cleavage- laminae, though to the eye appearing straight, being parts of large abrupt curves, with their summits cut off and worn down.
All attempts made to manufacture them in England had hitherto failed; the beating out of the iron by hammers into laminae sufficiently thin and smooth, and the subsequent distribution and fixing of the film of tin over the surface of the iron, proving difficulties which the English manufacturers were unable to overcome. To master these difficulties the indefatigable Yarranton set himself to work.
Again, I incidentally noticed in North Wales, where glaciers had passed over the truncated edges of the highly inclined laminae of clay-slate, that the surface, though smooth, was worn into small parallel undulations, caused by the competent laminae being of slightly different degrees of hardness.
Above this fossiliferous mass, there is a stratum of very fine-grained, pale brown mudstone, including numerous laminae of selenite. All the strata appear horizontal, but when followed by the eye for a long distance, they are seen to have a small easterly dip. On the surface we have the porphyritic gravel, and on it sand with recent shells.
Huxham reported to the Royal Society in 1748 the history of a child which was born with a tumor near the anus larger than the whole body of the child; this tumor contained rudiments of an embryo. Young speaks of a fetus which lay encysted between the laminae of the transverse mesocolon, and Highmore published a report of a fetus in a cyst communicating with the duodenum.
In all cases the acquirement of sensitiveness by the mid-ribs of the leaves appears to stand in some close relation with the abortion of their laminae or blades. The latter, therefore, are intermediate in nature between twiners and tendril-bearers, and ought to be related to both.
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