OPPONENTS AND OBJECTIONS. 191 



21st. This limited occurrence is an assumption contrary to 

 facts. It leaves out of account the Tudor specimens, and also 

 the abundant occurrence of the Stromatoporoid successors of 

 Eozoon in the Silurian and Devonian. Further, even if the 

 Eozoon were limited to the Laurentian, this would not be 

 remarkable ; and since all the Laurentian rocks known to us 

 more or less altered, it could not in that case occur in 

 Itered rocks. 



I have gone over these objections seriatim, because, though 

 individually weak, they have an imposing appearance in 

 the aggregate, and have been paraded as a conclusive settle- 

 ment of the questions at issue. They have even been re- 

 printed in the year just past in an English journal of some 

 standing, which professes to accept only original contributions 

 to science, but has deviated from its rule in their favour. I 

 may be excused for adding a portion of my original argument 

 ia opposition to these objections, as given more at length in 

 the Transactions of the Irish Academy. 



1. I object to the authors' mode of stating the question at 

 issue, whereby they convey to the reader the impression that 

 this is merely to account for the occurrence of certain peculiar 

 forms in ophite. 



With reference to this, it is to be observed that the attention 

 of Sir William Logan, and of the writer, was first called to 

 Eozoon by the occurrence in Laurentian rocks of definite 

 forms resembling the Silurian Stromatoporce, and dissimilar 

 from any concretions or crystalline structures found in "these 

 rocks. With his usual sagacity. Sir William added to these 

 facts the consideration that the mineral substances occurring 

 in these forms were so dissimilar as to suggest that the forms 

 themselves must be due to some extraneous cause rather than 

 1 any crystalline or segregative tendency of their constituent 

 minerals. These specimens, which were exhibited by Sir 

 William as probably fossils, at the meeting of the American 

 Association in 1859, and noticed with figures in the Eeport of 

 the Canadian Survey for 1863, showed under the microscope 

 no minute structures. The writer, who had at the time an 

 opportunity of examining them, stated his belief that if fossils, 

 they would prove to be not Corals but Protozoa. 



