288 NATURAL SCIENCE. April, 1895. 



Eozoon Canadense. 



I desire respectfully to take exception to two statements respecting Eozoon in 

 your issue for February (p. 75). 



The Tudor specimen of Eozoon is in no respect the " original " or type-specimen 

 of the fossil, but an exceptional form, from a distinct formation, and showing only 

 imperfectly the microscopic characters. That it is organic I have no doubt, and in 

 this matter I think my long experience as a collector of fossils of the older rocks 

 should give some weight to my judgment ; but its precise nature is, in any case, a 

 distinct question from that of the organic origin of the original Laurentian speci- 

 mens. The same remark applies to Archceozobn Acadiense, recently discovered in 

 the Pre-Cambrian rocks near St. John, New Brunswick, which appears to resemble 

 the Cambrian Cryptozoon of Hall rather than Eozoon ; and similar forms have been 

 found by Walcott below the Cambrian in Colorado. These, it may be hoped, will 

 ultimately throw light on the peculiarities of the probably Huronian specimens 

 from Tudor and Madoc. 



If, as you state, the specimens described by Drs. Johnston Lavis and Gregory, 

 are merely examples of "zonal alteration of blocks of limestone which have been 

 enclosed in an igneous magma," it is certain that they cannot be similar in origin to 

 Eozoon, which is not known to occur in such relations, and is evidently an original 

 structure in the limestone in which it is embedded, and from which small specimens 

 can sometimes be entirely isolated by treatment with an acid. I have made con- 

 siderable collections of banded contact rocks for comparison with Eozoon, but have 

 not found any to exhibit its characters. 



I have not yet seen the paper in the Dublin Transactions, and an application to 

 Dr. Johnston Lavis for a specimen of his material has as yet elicited no reply. In 

 the meantime I have no evidence that the conclusions of Dr. Gregory are any 

 nearer the truth than those of Rowney or Mobius. 



Montreal, February 5, 1895. J- Wm. Dawson. 



[We are afraid Sir William Dawson has misunderstood our remark about the 

 Tudor specimen of Eozoon. We did not say that this was the original or type-specimen 

 of Eozoon, but that the " original Tudor specimen " was sent to England and there 

 re-examined and shown to be inorganic. It was shown at the same time that the 

 Tudor specimen was in no way connected with the original specimens of Eozoon, and 

 that the claim that Eozoon had been found in carbonate of lime alone, free from 

 magnesian silicates, could not be substantiated. A section of the paper by Professor 

 Johnston Lavis and Dr. Gregory discusses the mode of occurrence of the normal 

 original specimens, and shows that the true Eozoon has probably originated by exten- 

 sive alteration of limestone blocks and their absorption of ferro-magnesian silicates. 



We regret that we are unconvinced by Sir Wm. Dawson's arguments, but we 

 are always pleased to hear what he has to say. — Editor.] 



" Anlagen, Rudiments, and Blasts." 



We have received a letter from Dr. Herbert Hurst maintaining that Darwin 



does not use the term rudiment "in the sense of an organ or structure which has 



been at one time more complicated than it is at present," and that rudiment is an 



exact translation of the German " Anlage " so far as this term is used in embryology. 



An Omission. 

 We regret that no mention was made of the fact that the excellent photograph 

 of the British Museum Archiropteryx, which we were permitted to reproduce in our 

 last number, was taken by Mr. A. Gepp, to whose skill we and our readers are 

 greatly indebted. 



