LUA 



LLIAM8.] OWEN. 141 



lining groups. Owen subsequently changed these last two correla- 

 tions. 



In a footnote 1 Owen mentioned Hall's substitution of the term Nia- 

 gara for " Cliff limestone," and on page 28 of the same document he 

 stated : 



A review of the fossils of the region under consideration proves, however, that tlio 

 Cliff formation of Iowa and Wisconsin is, in point of fact, the American equivalent 

 of the Upper and perhaps of part of the Lower Silurian formations of Murchison. 2 



Owen introduced another distinction which is of great importance, 

 but would scarcely be noticed were we not watching for it. In the 

 House edition of the report, the table giving the rocks of Iowa and 

 Wisconsin has "Carboniferous or Mountain limestone" for the rocks 

 below the Coal Measures, 3 and the revised edition 4 has " Subcarbonif- 

 erous limestone or Protozoic rocks" in its place, and on page 32 is 

 added a clause describing the "Carboniferous limestone of Iowa." 

 Under this heading the author included the reddish limestones of Kock- 

 ingham, Iowa, 5 and some dark encrinital layers near Stevenson, Illinois. 



The "white limestones " of the same part of the State the author 

 reported as contemporaneous with the "shell beds " on the Falls of the 

 Ohio, and as representing by their fossils the Onondaga, Corniferous, 

 Marcellus, and Hamilton groups of New York. 



The geological chart 6 has a legend which gives the following classi- 

 fication for the part of the scale here under consideration : 



Northwest margin of Great Illinois coal field. 

 Subcarboniferous limestone. 

 Shell stratum. 



Cliff rocks of the West ? < Coralline beds. 



Upper Magnesian limestone S I Lead-bearing beds. 



Blue Fossiliferous limestone. 

 Etc. 



On comparing the two editions of the report it becomes evident that 

 a study of Hall's report of the Fourth District of New York, in which a 

 comparison is made with Murchison's Silurian system, convinced Owen 

 that his " Cliff limestone and Blue limestone " were representatives of 

 Silurian rocks. 



In the Senate edition of the report as published in 1844, Owen stated : 



A review of t he fossils of the region under consideration proves that the Cliff 

 formation of Iowa and Wisconsin is, in point of fact, the American equivalent of the 

 Upper, and perhaps of part of the Lower, Silurian formation of Murchison. 



It will be remembered that at this time the Lower Devonian, as far 

 up as the Hamilton formation inclusive, was identified with the Silurian 



1 Senate Document 407, page 23. 



* He had just remarked upon the identity of the Cliff limestone of America with the Scar limestone 

 of England. 



8 Doc. 239, p. 22. 



* Senate Doc. 407, XXVIIIth Congress, first session, pp. 27-32. 

 6 Previously called Archimedes beds. 



6 PL 3 of the Senate document. 



