XIII.] ORIGIN OF CRYSTALLINE ROCKS. 303 



with the one or the other of these silicates in such a manner as 

 to make it evident that they had replaced the sarcode of the 

 animal, precisely as glauconite and similar silicates have, from 

 Cambrian times to the present, filled and injected more recent 

 foraminiferal skeletons. I recalled, in. connection with this 

 discovery, the observations of Ehrenberg, Mantell, and Bailey, 

 and the more recent ones of Pourtales, to the effect that glau- 

 conite or some similar substance occasionally fills the spines of 

 Echini, the cavities of corals and millepores, the canals in the 

 shells of Ealanus, and even forms casts of the holes made by 

 burrowing sponges (Clionia) and worms. The significance of 

 these facts was further illustrated by showing that the so- 

 called glauconites differ considerably in composition, some of 

 them containing more or less alumina or magnesia, and one 

 from the tertiary limestones near Paris being, according to 

 Berthier, a true serpentine.* 



These facts in the history of Eozoon were first made known 

 by me in May, 1864, in the American Journal of Science, and 

 subsequently more in detail, February, 1865, in a communi- 

 cation to the Geological Society of London. t They were 

 speedily verified by Dr. Giimbel, who was then engaged 

 in the study of the ancient crystalline schists of Bavaria, and 

 soon recognized the existence, in the limestones of the old 

 Hercynian gneiss, of the characteristic Eozoon Canadense, 

 injected with silicates in a manner precisely similar to that 

 observed by Dawson and myself.^ Later, in 1869, Robert 

 Hoffmann described the results of a minute chemical examina- 

 tion of the Eozoon from Raspenau, in Bohemia, confirming 

 the previous observations in Canada and Bavaria. He showed 

 that the calcareous shell of the Eozoon, examined by him, 

 had been injected by a peculiar silicate, which may be de- 

 scribed as related in composition both to glauconite and to 



* American Journal of Science (2), XL. 360 ; Report Geol. Survey of Can- 

 ada, 1866, p. 231 ; and Quar. Geol. Jour., XXI. 71. 



t American Journal of Science (2), XXXVII. 431 ; Quar. Geol. Jour., XXI. 

 67. 



J Proc. Royal Bavar. Acad. for 1866 ; and Can. Naturalist, new series, 

 III. 81. 



