62 PKOCEEDINGS OF THE NATIONAL MUSEUM vol.76 



gists in correlating the mentioned formations with each other and 

 also, though somewhat more loosely, with the Lyckholm and Bork- 

 holm of the Baltic region. They agree, further, in referring them all 

 to the upper part of the Ordovician system. Perhaps, and I may 

 even say probably, they are right in holding to this opinion so long as 

 the base of the Llandovery in Wales, the Rastritesskiffer in Sweden, 

 and the Addifir in Estonia are insisted on as marking the base of 

 the succeeding system. But is their apparently still uncompromising 

 attitude on this question warranted by the changing needs of a grow- 

 ing science ? I have thought and still think it is not. 



On various occasions, but especially in my most recent paper on 

 the Ordovician-Silurian boundary ,^^ I have cited and discussed many 

 facts that show that this is not the most natural nor the most widely 

 recognizable boundary nor the one that marks the beginning of 

 physical conditions that distinguish the new period and sets it apart 

 from the preceding. Besides, the contact of the Llandovery with 

 the Bala and Caradoc, which Lapworth in 1879 designated as the 

 boundary between his newly proposed Ordovician and the restricted 

 Silurian system of Murchison, does not correspond to the boundary 

 between the Champlain and Ontario divisions of the New York 

 system that were proposed by Emmons and his associates on the 

 New York Survey in 1842 and which since then have been generally 

 abandoned in favor of the no better defined and, in their present 

 significance, much younger British terms. I am not a sufficiently 

 strict adherent to the law of priority to object to this usurpation of 

 terms, but I do object to the abandonment of those features of tlie 

 original New York classification that in my opinion give a better 

 and more natural classification of the concerned parts of geological 

 history. 



The advantage of the original definition of the term Ontario (or 

 Ontarian as Dana amended it in 1890) over the definition of the re- 

 stricted Silurian system that now prevails rather generally in 

 Europe lies in the fact that both its lower and upper boundaries as 

 delimited by Emmons in 1842 are more consistent with nature's 

 definition ^^ of the period to which it was applied than is Lapworth 's 

 redefinition of the term Silurian that has been adopted by most 

 American geologists since 1879 without adequate investigation of its 

 fitness as a major term in the classification of American formations. 

 Emmons defined the " Ontario group " as overlying the Champlain 

 group and underlying the Helderberg series and as including the 

 Manlius at the top and the Medina sandstone at the base. This defi- 

 nition accords precisely with the system of rocks in America for 



'1 Relative values of criteria used in drawing the Ordovician-Silurian boundary, Geol. 

 Soc. America Bull., vol. 37, pp. 279-348, 1926. 

 «2Ulrlch. E. O., Idem, p. 326, 1926. 



