Association of American Geologists and Naturalists. 163 
group, which were very similar if not identical with those of the 
Clinton group. But he had never seen any thing resembling the 
Dictuolites, except in the Medina sandstone. Both these forms 
might have been called into existence at the period of the Hud- 
son River group, and the conditions favoring their existence have 
never recurred till the subsequent periods of the Medina sand- 
stone and the Clinton group. 
Both the Hudscn River group and the Clinton group are at 
distinct points exceedingly different in composition, being at one 
point almost wholly argillaceous and arenaceous, while at another 
they were calcareous. Where these are similar in lithological 
character, the fossils are very similar likewise, and perhaps some- 
times identical. A similar example occurs in the formations of 
the Niagara shale and the Delthyris shaly limestone, where sev- 
eral of the points are identical. In the latter there is a shell 
almost precisely similar to the Orthis canalis of Murchison, but 
larger and more resembling the O. elegantula of Dalman. 
Dr. Emmons enquired whether he had understood Mr. Hall 
correctly, as saying that he considered the Caradoc sandstones as 
equivalent to the Hudson River group. 
Mr. Hail replied in the affirmative, and remarked that they 
also evidently included the Clinton group. 
Dr. D. D. Owen then took up the reading of his paper, “on 
the Geology of the Western States,” where it was left at yester- 
day’s session. 
Beneath the black bituminous shale with which the previous remarks 
concluded, are thick beds of limestone, often magnesian, forming a mass 
varying from one hundred to five hundred feet in thickness, and occu- 
pying a vast superficial area, particularly in the north and northwest. 
This is the lead-bearing rock of Iowa and Wisconsin, and has yielded 
more lead than any other formation in the western states. ‘The actual 
produce of the mines situated in the Mineral Point district of Wiscon- 
sin and Northern Illinois, was in 1842, 32,000,000 lbs. of lead. 
It was remarked that in lithological character and mineral contents, 
the formation of this American lead region bore a strong resemblance 
to the ‘‘scar limestone” and great lead-bearing limestone of the North 
of England, a member of the carboniferous group, and that, were it 
not for the sure test furnished by a comparison of the organic remains, 
one would be strongly tempted to pronounce the formation in Iowa and 
Wisconsin identical with that of the lead region in Northern’ England ; 
whereas an investigation of the specific character of the fossils proves 
