76 THE DAWN OF LIFE. 



Devonian^ the Globigerinae and their allies in the chalk, 

 or the Nummulites and Miliolites in the Eocene. The 

 two latter groups of rock-makers are represented in 

 our cut, fig. 21 ; the first will engage our attention in 

 chapter sixth. It is a remarkable illustration of the 

 constancy of natural causes and of the persistence of 

 animal types_, that these humble Protozoans, which be- 

 gan to secrete calcareous matter in the Laurentian 

 period, have been continuing their work in the ocean 

 through all the geological ages, and are still busy in 

 accumulating those chalky muds with which recent 

 dredging operations in the deep sea have made us so 

 familiar. 



NOTES TO CHAPTER IV. 



(A.) Original Description op Eozoon Canadense. 



[As given by the author in the Journal of the Geological Society, 

 February, 1865.] 



" At the request of Sir W. E. Logan, I have submitted to 

 microscopic examination slices of certain peculiar laminated 

 forms, consisting of alternate layers of carbonate of lime and 

 serpentine, and of carbonate of lime and white pyroxene, 

 found in the Laurentian limestone of Canada, and regarded by 

 Sir William as possibly fossils. I have also examined slices 

 of a large number of limestones from the Laurentian series, 

 not showing the forms of these supposed fossils. 



" The specimens first mentioned are masses, often several 

 inches in diameter, presenting to the na,ked eye alternate 

 laminsB of serpentine, or of pyroxene, and carbonate of lime. 

 Their general aspect, as remarked by Sir W. E. Logan 

 {Geology of Canada, 1863, p. 49), reminds the observer of that 

 of the Silurian corals of the genus Stromatopora, except that 



