HISTORICAL SKETCH. X1X 
“From the evidence it is clear that the limestone of Galena, Illinois, and of Mineral Point, Wis.. 
in which the lead occurs, is certainly not of more recent date than the Pulaski and Lorraine shales of 
New York, and the Caradoc sandstone of Great Britain; but I believe it will prove to be an upper member 
of the Trenton limestone formation.” 
In the lead-bearing rock, ‘‘a buff, granular limestone,” Mr. Conrad reported the fol- 
lowing as having been identified: 
Inachus pervetus Con. Orthis testudinaria? 
Pleurotomaria angulata Sow. Delthyris — 
Turritella — Strophomena sericea 
Cyathophyllum profundum Con. 
The following are definitely located at Mineral Point, Wis.: 
Crytoceras marginalis Con. Orthis disparilis Con. 
Orthoceras annellus Con. Orthis perveta Con. 
Phragmolites compressus Con. Orthis tricenaria Con. 
Turritella — Orthis bellarugosa Con. 
Pleurotomaria angulata Sow. Orthis subequata Con. 
Bellerophon bilobatus Sow. Atrypa schlottheimi Von Buch. 
Euomphalus triliratus Con. Nuculites — 
Inachus pervetus Con. Nuculites — 
Subulites elongata. Delthyris — 
Strophomena sericea Sow. Ceraurus pleurexanthemus Green. 
Strophomena deflecta Con. Tsotelus gigas DeKay. 
Strophomena recta Con. Thaleops ovata Con. 
Orthis testudinaria? Cytherina fabulites Con. 
Several of the foregoing are new species, described here for the first time. Mr. Con- 
rad should have the credit of first determining the age of these rocks correctly from 
adequate data. His studies were the basis of the statement of Mr. Nicollet made the same 
year. It is known that Mr. Nicollet had the aid and co-operation of Mr. Conrad. 
J. N. Nicollet. 
1843. Report intended to illustrate a map of the hydrographical basin of the upper Mis- 
sissippt river, made by J. N. NicoLuET, Washington, 1843. 20th Congress, 2d Session; 
Senate doc. 237, pp. 1-170. 
Very little of this report is devoted to geology. The rocks of the Undine region 
(valley of the Blue Earth river) and of the lower half of the Minnesota valley are con- 
sidered to be the same as those at Fort Snelling—i. e., a thick friable sandstone overlaid 
by limestone, sometimes magnesian and occasionally containing fossils (pp. 19-20). He 
considers these rocks as Silurian (p. 30) and gives approximately the outlines of the 
Silurian, or, as he terms it, the formation of St. Peter’s (p. 71):—‘‘The geological form- 
ation of St. Peter’s continues to show itself in the river of the same name,* and goes on 
thinning out as far as Waraju river (the riviere aux Liards of the French) and there it dis- 
appears. Hence it passes to the head waters of the Mankato* river, crosses the southern 
part of the Coteau des Prairies, and finally loses itself in the Missouri, Sioux and Iowa 
rivers. * * * * To the east, starting from St. Anthony falls, it may conjecturally be 
stated to cross the St. Croix, make its appearance on Manomin, Chippeway and Sapak 
rivers, not far from the rapids and falls of these rivers, and then, passing through the 
*The Minnesota river was formerly called the St. Peter. 
*Now known as the Blue Earth. 
