BOSS — ON EVOLUTION. 4^1 



them downwards in the rocks — backwards in time — speaks of the 

 life of the past as suggesting the idea of an inverted truncated 

 cone. 



Dana estimates the maximum thickness of the Tertiary rocks at 

 two miles, the Mesozoic at two miles, the Carboniferous at two 

 two-thirds miles, the Devonian at two two-thirds miles, and the 

 Silurian at four miles — thirteen and one-third miles in all. Accord- 

 ing to Sir Wm. Logan the Cambrian and Laurentian Formations 

 have in Canada a thickness of about seven one-half miles, and it is 

 at the base of these that Eozoon (so called) has been found, 

 forming a fitting apex to the cone. 



The Protozoa, at the base at once of the animal and veo-etable 

 Kingdoms, are found, ii Eozoon canadense and Eozoon bavaricum 

 are really of organic origin, as claimed by Dr. Dawson and others, 

 far below, that is, of an earlier period, than any other well recog- 

 nized organic remains. Most of the existing Protozoans are 

 microscopic. They have been classified as Plant-like, Eadiate-like, 

 Mollusk-like, and Articulate-like; a classification which indicate 

 plainly in these — w^hich it can scarcely be doubted are representative 

 of the earlier organisms in the same sense that the Fishes uf the 

 present day are representative of the earlier Fishes, that is differen- 

 tiated asymmetrical modifications of the earlier types — there exists 

 a tendency to the differentiations which are fully developed in the 

 great groups of organic structure next above the Protozoa, alike 

 in rank and in the period of their development. 



The lowest Plants (^Algce) are reproduced by spores (seeds or 

 eggs) which develope powers of motion, swimming about freely by 

 means of vibratile cilia, until, after a time, each attaches itself to a 

 rock or other object, and develops into a plant which has no lono-er 

 the power of voluntary motion, even in its free extremity. Very 

 similar is the planula of the Polyp, having like locomotive powers 

 until it too fixes itself on some object, retaining,. hov^ever, the power 

 of motion in its free extremity. Indeed very many forms that were 

 once classed with the Protozoa, are now known to be only the 

 mere embryonic forms of the lowest Plants, Radiates, or Articu- 

 lates, just as the embryonic forms of the higher Radiates have been 

 classed as Polyps, and of the higher Articulates as Worms. 



