Serpentine is a mineral which has been produced in different ways. Some igneous or volcanic rocks consist largely of compounds of silica and magnesia (olivine, etc.). When these rocks have become cold and are exposed to the action of water, they sometimes absorb this and become hydrated, thus passing into a kind of serpentine. When such rocks are pulverized and dispersed as volcanic ash, this falling into the sea may be there hydrated, and may form serpentinous layers, or in a fine paste or in solution may pass into the pores and cavities of shells and other organic things, acting, as we have seen, in the same manner with ordinary glauconite. In like manner serpentine of this origin may form nodules or grains in limestones, in consequence of its particles being aggregated together by concretionary attraction. We have already seen that some comparatively modern so-called glauconites are essentially of the nature of serpentine, and we know that in the old Laurentian sea, salts of magnesia and magnesian minerals were abundant, so that serpentinous minerals might play a greater part than they do in the modern seas. Loganite, the mineralizing substance of the Burgess Eozoon, is different from serpentine, yet closely allied to the glauconites. The presence of pyroxene may be explained in a similar way. It is a frequent constituent of bedded volcanic rocks and of volcanic ashes, and beds of it occur in the Grenville series which once, no doubt, were ash-beds. Layers of it also occasionally occur from a similar cause in the limestone, and crystals of it have been deposited by water in the veins passing through the limestones and schists. Dr. Johnston-Lavis has described in the July number of the _Geological Magazine_ for 1895 the aqueous deposition at ordinary temperature of crystals of pyroxene and hornblende, in cavities and crevices of bones included in an ash-bed of recent date, and in presence of calcite, apatite, and fluoride of calcium, as in the Grenville series. This is a modern instance analogous to that suggested above. Hence all these minerals filling the cavities and canals of Eozoon may have been deposited by water at ordinary temperatures, and have no connection with the alteration to which the beds have been subsequently subjected. I may add here that a Tertiary glauconite from the Calcaire Grossier of Paris analysed by Berthier[33] is essentially a serpentine composed of silicate of iron and magnesia, that Loganite as analysed by Hunt contains thirty-one per cent, of magnesia, and that Hoskins has shown[34] that modern glauconites often contain large proportions of magnesia and equivalent bases. [Footnote 33: Beudant, _Mineralogie_, xi. 178.] [Footnote 34: _Geological Magazine_, July, 1895.]