112 THE DAWN OF LIFE. 



broken up and imbedded in the rock. I have ascer- 

 tained with respect to these fragments of Eozoon_, that 

 they occur abundantly in certain layers of the Lauren- 

 tian limestone^ beds of some thickness being in great 

 part made up of them, and coarse and fine fragments 

 occur in alternate layers, like the broken corals in 

 some Silurian limestones. 



Finally, on this part of the subject, careful observa- 

 tion of many specimens of Laurentian limestone which 

 present no trace of Eozoon when viewed by the naked 

 eye, and no evidence of structure when acted on with 

 acids, are nevertheless organic, and consist of fragments 

 of Eozoon, and possibly of other organisms, not infil- 

 trated with silicates, but only with carbonate of lime, 

 and consequently revealing only obscure indications of 

 their minute structure. I have satisfied myself of 

 this by long and patient investigations, which scarcely 

 admit of any adequate representation, either by words 

 or figures. 



Every worker in those applications of the microscope 

 to geological specimens which have been termed micro- 

 geology, is familiar with the fact that crystalline forces 

 and mechanical movements of material often play the 

 most fantastic tricks with fossihzed organic matter. In 

 fossil woods, for example, we often have the tissues 

 disorganized, with radiating crystallizations of calcite 

 and little spherical concretions of quartz, or dissemina- 

 ted cubes and grains of pyrite, or little veins filled 

 with sulphate of barium or other minerals. We need 

 not, therefore, be surprised to find that in the vener- 



