L. We have seen enough, children, though very little of what might be seen if we had more time, of mineral structures produced by visible opposition, or contest among elements; structures of which the variety, however great, need not surprise us: for we quarrel, ourselves, for many and slight causes,--much more, one should think, may crystals, who can only feel the antagonism, not argue about it. But there is a yet more singular mimicry of our human ways in the varieties of form which appear owing to no antagonistic force; but merely to the variable humor and caprice of the crystals themselves: and I have asked you all to come into the schoolroom to-day, because, of course, this is a part of the crystal mind which must be peculiarly interesting to a feminine audience. (Great symptoms of disapproval on the part of said audience.) Now, you need not pretend that it will not interest you; why should it not? It is true that we men are never capricious; but that only makes us the more dull and disagreeable. You, who are crystalline in brightness, as well as in caprice, charm infinitely, by infinitude of change. (Audible murmurs of "Worse and worse!" "As if we could be got over that way!" Etc. The LECTURER, however, observing the expression of the features to be more complacent, proceeds.) And the most curious mimicry, if not of your changes of fashion, at least of your various modes (in healthy periods) of national costume, takes place among the crystals of different countries. With a little experience, it is quite possible to say at a glance, in what districts certain crystals have been found; and although, if we had knowledge extended and accurate enough, we might of course ascertain the laws and circumstances which have necessarily produced the form peculiar to each locality, this would be just as true of the fancies of the human mind. If we could know the exact circumstances which affect it, we could foretell what now seems to us only caprice of thought, as well as what now seems to us only caprice of crystal: nay, so far as our knowledge reaches, it is on the whole easier to find some reason why the peasant girls of Berne should wear their caps in the shape of butterflies; and the peasant girls of Munich theirs in the shape of shells, than to say why the rock-crystals of Dauphine should all have their summits of the shape of lip-pieces of flageolets, while those of St. Gothard are symmetrical, or why the fluor of Chamouni is rose-colored, and in octahedrons, while the fluor of Weardale is green, and in cubes. Still farther removed is the hope, at present, of accounting for minor differences in modes of grouping and construction. Take, for instance, the caprices of this single mineral, quart;--variations upon a single theme. It has many forms; but see what it will make out of this ONE, the six-sided prism. For shortness' sake, I shall call the body of the prism its "column," and the pyramid at the extremities its "cap." Now, here,