_Why are garnets often found of a reddish brown tinge?_
Because of the excess of oxide of iron which they contain; a small proportion being sufficient to colour them entirely, without injuring their play and splendour. In fact, the perfection of all gems depends less on the quality of their component principles, than on their complete solution and intimate combination. The alkalized earths, as lime, magnesia, and still better, pot-ash, seem to intervene as solvents, for alumina, completely dissolved, acquires, as we have shown from Klaproth, a crystallization, of which, by itself, it is not susceptible.
The garnet is found in Bohemia, Ceylon, and other countries; but the chief mart formerly being Sirian, the capital of Pegu, the best are often denominated Sirian garnets. The colour most esteemed is blood or cherry red, mixed often, however, with blue, forming tints of crimson, purple, and reddish violet; or orange red and hyacinth brown. The Sirian garnet is of a violet colour, which, in some rare specimens, makes it compete with the amethyst, from which it is to be discriminated by the disadvantage of losing its brilliancy, and acquiring an orange tint by candlelight. Distinct from all other garnets, it preserves its colour unmixed with the common black tinge, unassisted by foil, even when thick. _Course garnets_ are used as emery for polishing metals, and by lapidaries. They are found in Ireland, in Norway, and many other countries.
_Why are certain formations called marine?_
Because they result from continual deposits of shingle and sand, as may be seen on the flat coast of our eastern counties. In this manner, at Lowestoffe-Ness, as well as at Yarmouth, the sea has erected a series of natural embankments against itself. The present extent of land thrown up by the sea, and out of the reach of the highest tides, is nearly three miles long, projecting from the base of the original cliff to the distance of 660 yards at the Ness. The respective lines of growth are indicated by a series of small embankments, perfectly defined. Several of these ridges have been formed within the memory of men now living. A rampart of heavy materials is first thrown up by a violent gale from the north-cast. Sand is subsequently blown over, and consolidates the shingle, and the process is completed by marine plants taking root and extending their fibres in a kind of net-work through the mass. In process of time the surface becomes covered with vegetable mould, and ultimately, in many cases, is productive of good herbage.[5]