190 [ NovEMBER, 
A considerable portion of the southern and eastern part of this drift is 
based on the lowest protozoic sandstones of lower Silurian date; which forma- 
tion is best explored in a semicircular belt east of the Mississippi and up the 
valley of the Wisconsin as high as Point Boss; and bearing northeast to the 
Michigan boundary line. ; 
These lower Protozoic Sandstones have proved themselves far more fossili- 
ferous than the corresponding strata in the State of New York—the Potsdam 
sandstone; having yielded, besides the two small Lingulas, L. antigua and prima, 
of New York, four new genera of trilobites and at least nine or ten new species ; 
which is the more remarkable since no remains of crustaceans had previously 
been found lower than the Trenton, Black river:and Chazy limestones. 
In the ascending order succeeds the Lower Magnesian Limestone, reaching 
the surface to the southwest of the Protozoic sandstones ; characterized chiefly 
by gasteropodous mollusca, allied to Plewrotomaria, Ophileta and Strappa- 
rolus. They are represented by the deeper purple blue tints, and correspond in 
age to the calciferous sandrock of New York. 
With the intervention of non-fossiliferous sandstones, from forty to eighty 
feet in thickness, often composed of limpid grains of quartz, there is superim- 
posed on this formation, beds of shell-limestone of the age of the Trenton and 
Black river limestone of New York, and the blue limestones of Ohio and In- 
diana, containing Leptena alternata, sericea, deltoidea, Orthis testudenarta, 
occidentalis, subequata, Atrypa capax, modesta, Isotelus gigas, Calymena 
senaria, besides a great variety of other fossils found in the corresponding 
strata in Ohio, Indiana and New York, besides many new species. Though 
somewhat magnesian, these beds are the purest limestone of Silurian date in 
the district. 
Next succeeds, on the south, the lead-bearing beds of the upper magnesian 
limestone, colored Prussian blue, and containing Spirifer lynz, biforatus, Lin- 
gula quadrata and a few other fossils of the Trenton limestone, Utica slate and 
Hudson river group. ‘This formation is represented of a lighter shade of purple 
blue._ This part of the Upper Magnesian Limestone of Wisconsin has yielded 
latterly upwards of 50,000,000 of pounds of lead annually, and is about three 
hundred feet thick. 
The upper 200 feet of upper magnesian limestone of Wisconsin, form what 
we have designated the Coralline and Pentamerus beds, from the abundance of 
Catenepora escharotdes and Pentamerus oblongus, formed towards the top of this 
formation, which corresponds to the Niagara and Clinton groups of New York. 
To the southwest, of this, crossing the Mississippi, near its upper or Rock- 
island rapids, is a very pure calcareous formation, containing Atrypa reticularis, 
aspera, Orthis resupinata, Phocops macropthalma, and a variety of Spirifers, 
most of which are new species, allied to those of the Hamilton and Corniferous 
groups of New York, with extended hinge, and often with wide cardinal areas, 
and mostly smooth on the bourrelet or mesial fold. Also many of the corals 
found in the Onondaga limestone of New York and the limestones of the Eifel 
in Germany. 
Much of the limestone of this formation has a close texture, smooth surface 
and conchoidal fracture, approaching to lithographic limestones. 
The valley of the Mississippi, below Muscatine, is occupied by a zone of 
earboniferous limestone, which we divide into the upper and lower series, the 
former characterized by Lithostrotion basaltiforme, several species of Produe- 
tus, the Spirifers and Terebratule ; the latter by the Archimedes, a great variety 
of Pentramites and Crinoidea, Productus punctatus, Sptrifer cuspidatus, Sptrifer 
striatus, and remains of Pswmmodus and other fossil fishes; besides a variety 
of other species of organic remains. These beds of limestones encircle the 
Iowa and Missouri coal-field, and separate it from the Illinois coal-field, with 
which it may have been once in connection, before the denudation of the Mis- 
sissippi Valley; but they are now separated by a belt of from 25 to 50 miles 
of this subcarboniferous limestone, now encroached upon only by a few outliers 
of the coal measures near the Keokuk rapids of the Mississippi. 
The lowa and Missouri coal-field, now for the first time laid down on a geo- 
