Kelp, as it drifts and sways in the Atlantic, attracts from the sea both the iodine and the bromine dissolved in minute quantities in the sea-water. This trait of fastening upon a particular and rare element is displayed by plants on land as well as by sea-weeds. In the Horn silver mine of Utah, the zinc mingled with the silver is betokened by the abundance of a zinc violet, _Viola calaminaria_, a delicate cousin of the pansy. In Germany this little flower was believed to point to zinc deposits long before zinc was discovered in its juices. The late Mr. William Dorn, of South Carolina, had faith in a bush of unrecorded name, as declaring that gold veins stood beneath it: that his faith was not baseless is proved by the large fortune he won as a gold miner in the Blue Ridge country--his guide the bush aforesaid. Mr. Rossiter W. Raymond, a famous mining engineer of New York, has given some attention to “indicative plants” of this kind. He is of opinion that their unwritten lore among practical miners, prospectors, hunters, and Indians is well worth sifting. He says:--“Judging from the general laws of the distribution of plants, and from the analogy furnished by _Viola calaminaria_, we may expect that an indicative plant will be, not a distinct species, but a variety of some widely distributed species, the range of the species as a whole being determined by general conditions of climate, altitude and soil, while the characteristics of the variety are affected by causes peculiar to the mineral deposit. Temperature and moisture, as Agricola long ago pointed out, are among these causes, and color is one of the most sensitive of their effects. It is quite reasonable to believe the soil may affect the color of the plant absorbing it. On the other hand, it is not certain, even if a plant is proved to indicate by color or other peculiarities the presence of silver, that silver is the substance actually entering into and altering the plant. The effect may be due to some other mineral substances associated with the silver-ores; and our silver-plant may be indicative of silver in a silver region only.” Mr. Raymond remarks that a general relation between the flora and the geological formation of any given district is a fact familiar to field-geologists. Many plants, too, indicate the neighborhood of water. A botanist knowing the root-length, water-requirements and habits of different species can often determine from the surface vegetation, he tells us, the nature, amount and distance of the underground water-supply.[33] [33] In his paper on “Indicative Plants,” published in the Transactions of the American Institute of Mining Engineers, 1886, Mr. R. W. Raymond illustrated in natural size _Viola calaminaria_, _Amorpha crescens_, and _Erigonium ovalifolium_. His paper is followed by the interesting discussion it called forth.