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The Minerals Associates of Cassiterite.--These are much the same in Cornwall as have been observed in other tin-producing districts, as in Saxony, Bohemia, Brittany, Finland, Spain, the Malay Peninsula, Banca, Blitong, Queensland, New South Wales, Tasmania, &c. In the following lists of minerals which are associated with Cassiterite in the different kinds of country-rock in Cornwall, I only refer (a) to those which appear to have been formed contemporaneously with the Cassiterite, and (b) to those which have been observed in immediate contact with it and mostly deposited upon it.

The difficulty of devising a natural classification of minerals has been recognized by most mineralogical writers, and up to the present time no very satisfactory arrangement has been generally adopted. In the classification of the animal and vegetable kingdoms, although the systems have greatly varied from time to time, something like uniformity has pretty generally existed ever since Linnaeus proposed his famous system of double nomenclature ; but in mineralogy every writer does that which is right in his own eyes—not because there is no king—but because they are many and mutually antagonistic.

A few years ago, while inspecting some iron ore deposits at Smallacombe, near Bovey Tracey, in Devon, I noticed the occurrence of certain brightly colored green, red and brown clays in considerable quantity. I took several specimens of the green clay at the time, and on my return home laid them aside in a lumber closet, where they became buried with other specimens, from which they have only lately been disinterred. After so long a stay in a tolerably dry situation I thought they might be regarded as in a normally hygrometric condition, and it was in this state that I subjected then to examination and analysis, with the following results.