m 



VII 



TIfE DA WN OF LIFE 



T N the Grenvillian system, as represented in the 

 vicinity of the Ottawa River, perfect specimens 

 of Eozoon are found in one only of the principal 

 limestones there exposed, and in certain layers of 

 that limestone, and they are associated with 

 concretions and grains of the greenish mineral 

 serpentine, which, as we shall see, has much to do 

 with their preservation. As exposed on broken 

 surfaces, the specimens consist of concentric layers 

 of greenish serpentine and white calcite, not, however, 

 even or uniform, as in ordinary concretions having 

 concentric structure, but often approaching and 

 uniting with each other, so as to constitute wide 

 flat chambers, and forming patches from an inch to 

 nearly a foot in diameter, while some of the larger 

 patches seem to coalesce or to become confluent. 

 On weathered surfaces the serpentine laminae often 

 become brown, owing to the rusting of the iron 

 contained in them, and project above the general 



147 



