110 THE DAWN OP LIFE. 



a minutely granular or curdled appearance, arising no 

 doubt from the original presence of organic matter, 

 and not recognised in purely inorganic calcite. 



Another style of these remarkable fossils is that of 

 the Burgess specimens. In these the walls have been 

 changed into dolomite or magnesian limestone, and 

 the canals seem to have been wholly obliterated, so 

 that only the laminated structure remains. The 

 material filling the chambers is also an aluminous 

 silicate named loganite ; and this seems to have been 

 introduced, not so much in solution, as in the state of 

 muddy slime, since it contains foreign bodies, as grains 

 of sand and little groups of silicious concretions, some 

 of which are not unlikely casts of the interior of 

 minute foraminiferal shells contemporary with Eozoon, 

 and will be noticed in the sequel. 



Still another mode of occurrence is presented by a 

 remarkable specimen from Tudor in Ontario, and from 

 beds probably on the horizon of the Upper Laurentian 

 or Huronian.* It occurs in a rock scarcely at all 

 metamorphic, and the fossil is represented by white 

 carbonate of lime, while the containing matrix is a 

 dark-coloured coarse limestone. In this specimen the 

 material filling the chambers has not penetrated the 

 canals except in a few places, where they appear filled 

 with dark carbonaceous matter. In mode of preser- 

 vation these Tudor specimens much resemble the 

 ordinary fossils of the Silurian rocks. One of the 

 specimens in the collection of the Geological Survey 

 * See Note B, Chap. III. 



