546 Sir W. Daivson — The Animal Nature of Eozoon. 



tuberciilation gradually passes upward into smaller chambers, having 

 amoeboid outlines, and finally into rounded chamberlets. It is also 

 a very constant point of structure that the lower laminjB of calcite 

 are thicker than those above, and have the canal-systems larger and 

 coarser. There is thus in the more perfect specimens a definite plan 

 of macroscopical structure. 



Fig. 6. — Diagram of typical mode of arrangement of canals and tnbuli in a 

 lamina of JSozoon Canadense. (Magnified.) 



The normal mode of mineralization at Cote St. Pierre and Gren- 

 ville is that the laminje of the test remain as calcite, while the 

 chambers and larger canals are filled with serpentine of a light 

 green or olive colour, and the finer tubuli are injected with dolo- 

 mite. It may also be observed that the serpentine in the larger 

 cavities often shows a banded structure, as if it had been deposited 

 in successive coats, and the canals are sometimes lined with a tubular 

 film of serpentine, with a core or axis of dolomite, which also 

 extends into the finer tubuli of the surfaces of the laminfe. This, 

 on the theory of animal origin, is the most perfect state of pre- 

 servation, and it equals anything I have seen in calcareous organisms 

 of later periods. This state of perfection is, however, naturally of 

 infrequent occurrence. The finer tubuli are rarely perfect or fully 

 infilti-ated. Even the coarser canals are not infrequently imperfect, 

 while the laminae themselves are sometimes crumpled, crushed, 

 faulted, or penetrated with veins of chrysotile or of caicite. h\ 

 some instances the calcareous laminae are replaced by dolomite, in 

 which case the canal-systems are always imperfect or obsolete. The 

 laminae of the test itself are also in some coses I'eplaced by serpentine 

 in a flocculent form. At the opposite extreme are specimens or 

 portions of specimens in which tlie chambers are obliterated by 

 pressure, or occupied only with calcite. In such cases the general 

 structure is entirelj'^ lost to view, and scarcely appears in weather- 

 ing. It can be detected only by microscopic examination of slices, 

 in pai'ts where the granular structure or the tubulation of the calcite 

 layers has been preserved. All palseontologists who have studied 

 silicified fossils in the older rocks are familiar with such appearances. 



It has been alleged by Mobius and others that the canal- systems 

 and tubes pi-esent no organic regularity. This difficulty, however, 

 arises solely from imperfect specimens or inattention to the 

 necessary results of slicing any system of ramifying canals. In 

 Eozoon the canals form ramifying groups in the middle planes of 



