Page:Popular Science Monthly Volume 10.djvu/279

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265
THE EARLIER FORMS OF LIFE.

awakened hostile criticism and resulted in illustrating the presence of silicates in organisms in every age of the world. Formerly it was believed that carbonate of lime was the principal mineral found replacing organic substances, thus producing petrifactions. Now we have iron oxide, silica, clay, sand, sulphuret of iron, ores of copper, lead, etc., fluor-spar, heavy spar, phosphate of lime, all unmistakably occupying

PSM V10 D279 Portion of eozoon magnified 100 times.jpg
Fig. 4.—Portion of Eozoön magnified 100 Diameters. (After Carpenter.)
a a, Original cell-wall with tubulation; b c Supplementary skeleton, with canals; 2. Portion of a a magnified.

the place of decomposable organic material. And the discussions about Eozoön recall and enforce facts about the employment of silicates by Nature to preserve her structures, especially in foraminiferal forms. In New Jersey there are beds of green-sand of Cretaceous and Tertiary ages full of concretions composed of a silicate of iron and potash called glauconite. Owing to its value as a fertilizer, thousands of tons of it are annually employed by the farmers to enrich their lands. This silicate has replaced modern organic structures of various kinds, but noticeably corals, echinoderms, nummulites, and other rhizopods. The fine tubulation and pores of these microscopic structures have been penetrated by the silicates, so that, when the calcareous parts have been removed by acid, the insoluble glauconite residue shows us the forms of the chambers and cavities. This process of the infiltration of organisms by glauconite was known long before the discovery of Eozoön. It goes on at the present day at the bottoms of the warmer seas, as evidenced in the facts discovered by the numerous deep-sea dredgings recently undertaken in the interests of science. Dr. Hunt suggests that the mineral is developed through chemical reactions in the ooze at the sea-bottom, a combination of dissolved silica with iron put into the ferrous soluble condition by means of organic matter.