"It appears probable from these observations that glauconite is formed by chemical reactions in the ooze at the bottom of the sea, where dissolved silica comes in contact with iron oxide rendered soluble by organic matter; the resulting silicate deposits itself in the cavities of shells and other vacant spaces. A process analogous to this in its results, has filled the chambers and canals of the Laurentian _Foraminifera_ with other silicates; from the comparative rarity of mechanical impurities in these silicates, however, it would appear that they were deposited in clear water. Alumina and oxide of iron enter into the composition of loganite as well as of glauconite; but in the other replacing minerals, pyroxene and serpentine, we have only silicates of lime and magnesia, which were probably formed by the direct action of alkaline silicates, either dissolved in surface-waters, or in those of submarine springs, upon the calcareous and magnesian salts of the sea-water." [As stated in the text, the canals of Eozoon are sometimes filled with dolomite, or in part with serpentine and in part with dolomite.] (B.) Silurian Limestones holding Fossils infiltrated with Hydrous Silicate. Since my attention has been directed to this subject, many illustrations have come under my notice of Silurian limestones in which the pores of fossils are infiltrated with hydrous silicates akin to glauconite and serpentine. A limestone of this kind, collected by Mr. Robb, at Pole Hill, in New Brunswick, afforded not only beautiful specimens of portions of Crinoids preserved in this way, but a sufficient quantity of the material was collected for an exact analysis, a note on which was published in the Proceedings of the Royal Irish Academy, 1871.