The Af/e of the Ga/eita Limestone. — Winchell. 35 
nois this change is shown by the sudden ti-ansition from the 
Trenton limestone to the Thebes sandstone. There might be 
added to this general truth a further general law which per- 
tains to the Lower Silurian in North America, viz., that the 
Utica slate is followed by the Hudson River by a very gentle 
change, or is merged into the Hudson River so closely that 
the two formations cannot be separately identified in numer- 
ous places. Thus, Safford shows that in Tennessee the Nash- 
ville (Hudson River) involves the Utica slate. Although the 
slate is lithologically a dark shale, 100-150 feet thick, the 
characteristic graptolites are not confined to this stratum, 
but run up into the main body of the shale, and are found at 
numerous localities. Lithologically the Utica slate and the 
Hudson River formations usually are lost in each other, being 
linked together in all descriptions, their fossils even being put 
into the same chapter by James Hall in 1847. There is hardly 
an exception to this close union of the Utica slate with the 
Hudson River; indeed, as Mr. Walcott truly remarks, at the 
opening of his paper, the term Hudson River, with the Utica 
slate as a subdivision, has been generally received into geo- 
logical literature. 
In summarizing the paleoiitological data the following table 
is given by Mr. Walcott: 
Utica Galena. 
Total number oF species 100 7S 
Species limited lo the format ion •")4 lit 
Species limited to the fdrmalioii and the Tri'iitnn 
grou[) 11 2!l 
Species limited to the formations and the Hudson 
River formation 11 :{ 
Species common to the Trenton, Hudson Kivrr, 
and Utica and Galena formations "34 27 
Species passinj;' from the Trenton lo the Utica and ' 
Galena 'i~i •"><> 
Species passinji from the Utica or (ialena to the 
Hudson River :!•") :!0 
Of the 85 species, however, which pass from the Trenton to 
the Utica 10 are hardy species, ranging from the Chazy and 
Black River to the Utica. There is no way of telling, from 
Mr. Walcott's table of the fossils of the Utica slate (pp. 34-88), 
what part of the 56 species passing from the Trenton to the 
Galena had their commencement below the Trenton limestone. 
