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,^. antiqua qm A 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 Pleuroiomaria, Ophileia and Strappa- 

 rolus. They are represented by the deeper purple blue tinis, 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 Leptcena alternata, sericea, deltoidea, Orthis testudenarta, 

 occidentalism suboequata, Atrypa capax^ modesta, Isoielus ffiffas, 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 lynx^ hiforatus, Lin- 

 gula quidrata 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 esckaroides 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, Orthus 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 area?, 

 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 

 carboniferous limestone, which we divide into the upp^r and loner series, the 

 former characterized by Lithostrotion basalti/orme, several species of Produc- 

 tus, the Spirifers and Terebratulce ; the latter by the ^rc^mtf/e^, a great variety 

 of Pentramites and Crinoidea, Productus punctatus, Spirifer cuspida'us, Sptrifcr 

 striatus, and remains of Psammodus 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- 

 siesippi Valley; but they are now separated by a belt of from 25 to 50 miles 

 of this Bubcarboniferous limestone, now encroached upon only by a few outliers 

 of the coal measures near the Keokuk rapids of the Mississippi. 



The Iowa and Missouri coal-field, now for the first time laid down on a geo- 



