54 THE DAWN OF LIFE. 



higher in horizon than that of Grenville. From the village of 

 Madoc, the zone of gray micaceous limestone, which has been 

 particularly alluded to, runs to the eastward on one side of the 

 trough, in a nearly vertical position into Elzivir, and on the 

 other side to the northward, through the township of Madoc 

 into- that of Tudor, partially and unconformably overlaid in 

 several places by horizontal beds of Lower Silurian limestone, 

 but gradually spreading, from a diminution of the dip, from 

 a breadth of half a mile to one of four miles. Where it thus 

 spreads out in Tudor it becomes suddenly interrupted for a 

 considerable part of its breadth by an isolated mass of anortho- 

 site rock, rising about 150 feet above the general plain, and 

 supposed to belong to the unconformable Upper Laurentian." 



[Subsequent observations, however, render it probable that 

 some of the above beds may be Huronian.] 



"The Tudor limestone is comparatively unaltered : and, in the 

 specimen obtained from it, the general form or skeleton of the 

 fossil (consisting of white carbonate of lime) is imbedded in 

 the limestone, without the presence of serpentine or other 

 silicate, the colour of the skeleton contrasting strongly with 

 that of the rock. It does not sink deep into the rock, the 

 form having probably been loose and much abraded on what 

 is now the under part, before being entombed. On what was 

 the surface of the bed, the form presents a well-defined out- 

 line on one side ; in this and in the arrangement of the septal 

 layers it has a marked resemblance to the specimen first 

 brought from the Calumet, eighty miles to the north-east, and 

 figured in the Geology of Canada, p. 49 ; while all the forms 

 from the Calumet, like that from Tudor, are isolated, imbedded 

 specimens, unconnected apparently with any continuous reef, 

 such as exists at Grenville and the Petite Nation. It will be 

 seen, from Dr. Dawson's paper, that the minute structure is 

 present in the Tudor specimen, though somewhat obscure; 

 but in respect to this, strong subsidiary evidence is derived 

 from fragments of Eozoon detected by Dr. Dawson in a speci- 

 men collected by myself from the same zone of limestone near 

 the village of Madoc, in which the canal- system, much more 

 distinctly displayed, is filled with carbonate of lime, as quoted 



