DIFFICULTIES AND OBJECTIONS 23 I 



1. The Upper Laurentian of Canada, a rock forma- 

 tion whose distribution, age, and structure have been 

 carefully worked out in several extensive districts 

 by the Canadian Survey, is found to contain thick 

 and widely distributed beds of limestone, related 

 to the other beds in the same way in which lime- 

 stones occur in the sediments of other geological 

 formations. There also occur in the same forma- 

 tion, graphite, iron ores, and metallic sulphides, in 

 such relations as to suggest the idea that the lime- 

 stones as well as these other minerals are of organic 

 origin. 



2. In the limestones are found laminated bodies 

 of definite form and structure, composed of calcite 

 alternating with serpentine and other minerals. The 

 forms of these bodies suggested a resemblance to 

 the Silurian Stromatoporae, and the different mineral 

 substances associated with the calcite in the pro- 

 duction of similar forms showed that these were 

 not accidental or concretionary. 



3. On microscopic examination, it proved that 

 the calcareous laminae of these forms were similar 

 in structure to the shells of modern and fossil Fora- 

 minifera, more especially those of the Rotaline and 

 Nummuline types, and that the finer structures, 



