HISTORICAL SKETCH. XV 
James Hall. 
1842. Notes upon the geology of the western states, by JAMES HaLu. Am. Journ. Sci., 
vol. XLU, p. 51, April, 1842. See also Association of Geologists and Naturalists, 1840-42, 
pp. 267-298, Boston, 1848. 
This paper gives the generalized preliminary results of an extended tour made in 
1841 for the purpose of ascertaining how far the grouping of the New York strata, pub- 
lished in the New York reports, was applicable in the western extension of the New York 
system. It shows a masterly comprehension of the geographic areas occupied by the 
principal parts of the lower Paleozoic as far west as the Mississippi river and as far north 
as the coal fields of Michigan. In treating of the Cliff limestone of Ohio, supposed to be 
the equivalent of the Niagara limestone of New York, he adopted the determinations of 
the first survey by Owen (1839) in its applicationn to the lead region and fell into the 
error of placing the lead-bearing dolomyte of Wisconsin and Iowa (the Galena of later 
reports) in the “Cliff limestone,” and hence of making it a portion of the Niagara, here 
covering a thickness, according to measurements by Dr. John Locke, of five hundred and 
fifty feet. He, however, was of the opinion that some of the thin beds near the top of the 
Cliff limestone, as seen in Wisconsin and Iowa, should be assigned to the Lower Helder- 
berg. He states that the Niagara in western New York is known to contain ‘‘everywhere 
sulphurets of lead and zinc.” He formed the opinion that ‘‘the Ontario and Mohawk 
groups are both seen on the Mississippi above Dubuque,” underlain by a mass of sand- 
stone. That is, he was of the opinion that below the Galena (Niagara) the Hudson River 
and Trenton, as now known, existed. In this paper Prof. Hall indicated by the fossils 
which he named, that the ‘‘Blue limestone” at Cincinnati is to be considered the western 
representative of the Hudson River group of New York, which at that time was desig- 
nated by him the ‘Ontario group.” The inference which ought to have been drawn from 
this, viz., that the term Blue limestone could not be applied to the equivalent of the 
Trenton in the Mississippi valley, seems not to have been heeded, but that term has been 
perpetuated, even to the present time, at the lower horizon Later, howe ver, as will be 
seen, Prof. Hall applied the term ‘‘green and blue shales” to the Ontario group in the 
upper Mississippi valley. 
F. De Castelnau. 
1843. Essai sur le syst?me Silurien del Amérique septentrionale, par F. DE CASTELNAU, 
Consul général des Etats Unis 4 Lima, Membre de plusieurs sociétés savantes. Avec vingt- 
sept planches, Paris, 1843, 56 pp. and one geological map. 
This memoir was presented to the Academy of Sciences at the meeting of the 25th of 
August, 1842. A large number of fossils are figured. The region explored was chiefly 
that lying in the immediate vicinity of lakes Superior and Huron, and special attention 
was given to Drummond’s island and other islands near it. On these islands M. De Cas- 
telnau found large amounts of white dolomyte containing some forms of Huwronia and 
Euomphalus. This same formation of dolomyte—his ‘‘systéme magnésifére ’—extends 
