I5O WHAT MAY BE LEARNED FROM EOZOON 



been victimized, by having under their consideration only 

 specimens in which the actual characters had been too much 

 defaced to be discernible. No mistake can be greater than to 

 suppose that any and every specimen of Laurentian limestone 

 must contain Eozoon. More especially have I hitherto failed 

 to detect traces of it in those carbonaceous or graphitic lime- 

 stones which are so very abundant in the Laurentian country. 

 Perhaps where vegetable matter was very plentiful Eozoon did 

 not thrive, or, on the other hand, the growth of Eozoon may 

 have diminished the quantity of vegetable matter. It is also 

 to be observed that much compression and distortion have oc- 

 curred in the beds of Laurentian limestone and their contained 

 fossils, and also that the specimens are often broken by faults, 

 some of which are so small as to appear only on microscopic 

 examination, and to shift the plates of the fossil just as if they 

 were beds of rock. This, though it sometimes produces 

 puzzling appearances, is an evidence that the fossils were hard 

 and brittle when this faulting took place, and is consequently 

 an additional proof of their extraneous origin. In some speci- 

 mens it would seem that the lower and older part of the fossil 

 had been wholly converted into serpentine or pyroxene, or had 

 so nearly experienced this change that only small parts of the 

 calcareous wall can be recognised. These portions correspond 

 with fossil woods altogether silicified, not only by the filling of 

 the cells, but also by the conversion of the walls into silica. I 

 have specimens which manifestly show the transition from the 

 ordinary condition of filling with serpentine to one in which 

 the cell-walls are represented obscurely by one shade of this 

 mineral and the cavities by another. In general, however, it 

 will be gathered from the above explanations that the specimens 

 of Eozoon fall short in thoroughness of mineralization of some 

 fossils in much more modern rocks. I have specimens of 

 ancient sponges whose spicular skeletons, originally silicious, 

 have been replaced by pyrite or bisulphide of iron, and of 



