THE EARLIER FORMS OF LIFE. 



265 



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 replac- 

 ing 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 occu- 



%, 



Fig. 4. Portion op Eozoon magnified 100 Diameters. (After Carpenter.) 

 a o, Original cell-wall with tubulation ; b c, Supplementary skeleton, with canals ; 2. Portion of 



a a magnified. 



pying the place of decomposable organic material. And the discus- 

 sions about Eozoon recall and enforce facts about the employment of 

 silicates by Nature to preserve her structures, especially in foraminif- 

 eral 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 rhi- 

 zopods. 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 dis- 

 covery of Eozoon. 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 or- 

 ganic matter. 



