34 Principal J. W. Dawson on Eozoon canadense. 



difficulty in distinguishing these from the limited, tubercu- 

 lated, and Strom atoporoid chamber-casts oi Eozoon. 



6. The Canal-system. — I am not quite certain how Halm 

 regards this. To accord with his expansion theory, the canals 

 should be mere cracks or fissures ; and in one place he describes 

 them as such, though they are in reality cylindrical in form. 

 In another place he speaks of them as produced by the in- 

 jection of a fluid containing lime in solution into a more dense 

 fluid or semifluid substance. He objects to their being of 

 different dimensions, though this is a necessary result of their 

 ramifying into small branches. In regard to their composition, 

 he seems to state that they are entirely soluble in dilute acid, 

 and speaks of them as originating in crystals of aragonite — 

 though the fact is that large portions of them remain intact in 

 specimens treated with dilute acid, as he nmst have himself 

 observed. He appears also to suppose that they should show 

 a " tube or envelope " — which is not at all necessary, since, 

 according to the organic theory of Eozoon, they were oinginally 

 merely ramifying perforations in a calcareous skeleton. In 

 point of fact, in the ordinary serpentinous specimens the 

 chambers and chamberlets are in part filled with a flocculent 

 or porous serpentine, white by reflected light and brown by 

 transmitted light ; and this fills the larger canals ; but the finer 

 branches of these canals are often filled with calcite or Dolo- 

 mite. This mode of filling, which has been fully illustrated 

 by Dr. Carpenter and myself, does not, however, at all suit 

 the requirements of the olivine and expansion theory. 



He has, however, made the observation, for which he deserves 

 some credit, that " a canal-system does not generally extend 

 beyond one crystalline individual." There is an element of 

 truth in this, though it is not strictly correct. The canal- 

 systems are in general related to definite portions or thicken- 

 ings of the supplemental skeleton. These may often be called 

 in a certain sense crystalline individuals, their cleavage-planes 

 being uniform in direction. But otherwise it is not usual to 

 find the canals ceasing at interruptions of the crystalline struc- 

 ture, except in certain easily explicable cases. It is observable, 

 for instance, that the perfection of the structures and of the 

 crystallization are often in inverse ratio. Thus in portions 

 where the skeleton retains its granular character (regarded 

 apparently by Hahn as a " fluidal structure")* the canals are 



* The skeleton of Eozoon in its natural state seems to ha^-e been finely 

 porous, like that of Stromatopora, but on a more minute scale. This 

 f^-ives it a granular structure, often very distinct ; and in the Burgess 

 specimens the pores seem to have been filled with Dolomite, which re- 

 mains as a flocculent mass after the ealcite has been removed by dilute 



