1864.] DAWSON STRUCTURE OF EOZOON. 57 



sembling greensand- concretions ; and the manner in which these are 

 occasionally arranged in lines and groups suggests the supposition 

 that they may possibly be casts of the interior of minute Foramini- 

 feral shells. They may, however, be concretionary in their origin. 



4. In some of the Laurentian limestones submitted to me by Sir 

 W. E. Logan, and in others which I collected some years ago at 

 Madoc, Canada West, there are fibres and granules of carbonaceous 

 matter, which do not conform to the crystalline structure, and present 

 forms quite similar to those which in more modern limestones result 

 from the decomposition of Algae. Though retaining mere traces of 

 organic structure, no doubt would be entertained as to their vegetable 

 origin if they were found in fossiliferous limestones. 



5. A specimen of impure limestone from Madoc, in the collection 

 of the Canadian Geological Survey, which seems from its structure to 

 have been a finely laminated sediment, shows perforations of various 

 sizes, somewhat scolloped at the sides, and filled with grains of rounded 

 siliceous sand. In my own collection there are specimens of mica- 

 ceous slate from the same region, with indications on their weathered 

 surfaces of similar rounded perforations, having the aspect of ScoUtJms, 

 or of worm-burrows. 



I would observe, in conclusion, that the researches detailed in this 

 paper must be regarded as merely an introduction to a most interest- 

 ing and promising field of research. The specimens to which I had 

 access were for the most part collected by the explorers of the Sur- 

 vey merely as rocks, and without any view to the possible exist- 

 ence of fossils in them. It may be hoped, therefore, that other and 

 more perfect specimens may reward a careful search in the localities 

 from which those now described have been obtained. Further, 

 though the abundance and wide distribution of Eozoon, and the im- 

 portant part it seems to have acted in the accumulation of limestone, 

 indicate that it was one of the most prevalent forms of animal ex- 

 istence in the seas of the Laurentian period, they do not imply the 

 non-existence of other organic beings. On the contrary, independ- 

 ently of the indications afforded by the limestones themselves, it is 

 evident that in order to the existence and growth of these large 

 Ehizopods, the waters must have swarmed with more minute animal 

 or vegetable organisms on which they could subsist. On the other 

 hand, though this is a less certain inference, the dense calcareous 

 skeleton of Eozoon may indicate that it also was liable to the attacks 

 of animal enemies. It is also possible that the growth of Eozoon, or 

 the deposition of the serpentine and pyroxene in which its remains 

 have been preserved, or both, may have been connected with certain 

 oceanic depths and conditions, and that we have as yet revealed to 

 us the life of only certain stations in the Laurentian seas. 



Whatever conjectures we may form on these more problematic 

 points, the observations above detailed appear to establish the follow- 

 ing conclusions : — First, that in the Laurentian period, as in sub- 

 sequent geological epochs, the Rhizopods were important agents in 

 the accumulation of beds of limestone ; and, secondly, that in this 

 early period these low forms of animal life attained to a development. 



