"In connection with the Eozoon it is interesting to examine more carefully into the nature of the matters which have been called glauconite or green-sand. These names have been given to substances of unlike composition, which, however, occur under similar conditions, and appear to be chemical deposits from water, filling cavities in minute fossils, or forming grains in sedimentary rocks of various ages. Although greenish in colour, and soft and earthy in texture, it will be seen that the various glauconites differ widely in composition. The variety best known, and commonly regarded as the type of the glauconites, is that found in the green-sand of Cretaceous age in New Jersey, and in the Tertiary of Alabama; the glauconite from the Lower Silurian rocks of the Upper Mississippi is identical with it in composition. Analysis shows these glauconites to be essentially hydrous silicates of protoxyd of iron, with more or less alumina, and small but variable quantities of magnesia, besides a notable amount of potash. This alkali is, however, sometimes wanting, as appears from the analysis of a green-sand from Kent, in England, by that careful chemist, the late Dr. Edward Turner, and in another examined by Berthier, from the calcaire grassier, near Paris, which is essentially a serpentine in composition, being a hydrous silicate of magnesia and protoxyd of iron. A comparison of these last two will show that the loganite, which fills the ancient Foraminifer of Burgess, is a silicate nearly related in composition. I. Green-sand from the _calcaire grossier_, near Paris. Berthier (cited by Beudant, "Mineralogie," ii., 178). II. Green-sand from Kent, England. Dr. Edward Turner (cited by Rogers, Final Report, Geol. N. Jersey, page 206). III. Loganite from the Eozoon of Burgess. IV. Green-sand, Lower Silurian; Red Bird, Minnesota. V. Green-sand, Cretaceous, New Jersey. VI. Green-sand, Lower Silurian, Orleans Island. The last four analyses are by myself." I. II. III. IV. V. VI. Silica 40·0 48·5 35·14 46·58 50·70 50·7 Protoxyd of iron 24·7 22·0 8·60 20·61 22·50 8·6 Magnesia 16·6 3·8 31·47 1·27 2·16 3·7 Lime 3·3 2·49 1·11 Alumina 1·7 17·0 10·15 11·45 8·03 19·8 Potash traces 6·96 5·80 8·2 Soda ·98 ·75 ·5 Water 12·6 7·0 14·64 9·66 8·95 8·5 ---- ---- ------ ----- ------ ----- 98·9 98·3 100·00 100·00 100·00 100·0