52 PROTOZOIC ROCKS 
portion of the sections at Prairie du Chien; so that there was an entire absence of 
all palwontological evidence as to the exact place which these strata occupied in 
the Western geological series. It is, therefore, with no small degree of satisfaction 
that I find myself able to disclose a new feature in the paleontology of Western 
America, and thus to furnish, not only to the geologist a key to the stratigraphical 
position of the rocks north of the Wisconsin River, but, at the same time, to the 
miner his surest and safest guide by which to direct operations in the search after 
mineral wealth. 
The following table exhibits the most persistent elements of stratification of this 
Great Sandstone Formation ; showing the relative position of the different Trilobite 
beds, and the thickness of the intervening strata. 
TABLE OF THE ELEMENTARY STRATIFICATION OF THE LOWEST PROTOZOIC 
SANDSTONES. FORMATION 1. 
Feet. Inches. 
Quartzose, light-coloured sandstones, of various degrees of indu- 
ration, with intercalations of beds of Magnesian Limestone, 
Sixth Trilobite with glistening crystalline facets, and calcareo-siliceous 
2 odlite, produced by rounded grains of quartz, encased in cal- 
J careous cement, containing Huomphalus and as Tri- 
lobites. Locally, with a band of green earth, . . 50 to 85 ‘ 
Mammillary and botryoidal layer of white sandstone ; some- 
times banded with yellow, dD to 6 
( Thick beds of soft, yellowish, on Coes ies. sce no 
e ( with botryoidal, hard, projecting concretions, passing down 
7 wards into fine-grained, soft sandstones, approaching tripoli, 40 to 50 
beds, containing Dikelocephalus Minnesotensis. 
Stillwater Trilobite bed, 8 to 10 
Green, red, and yellowish ports with = ee, 
dolomitic intercalations, . 40 
Upper, brown dolomitic layers, tating Orthis, phipihes; 
and columns of Crinoidea, as at La Grange Mountain, E 4 
Fourth Trilobite |" pr of yellow, laminated cients with green 
bed. 
 -Fitth Trilobite Ash-coloured and yellowish argillo-caleareous and magnesio- 
Wed: | calcareo 
icles disseminated, . , 5 
Marine Mill Trilobite grit, . 4) 
Fucoidal layers, and dita vena: green ait jek sindieohel? ; 
“a at their base; often a band of about six inches of green earth, 
: used = the teaiay as a re E . 80 to 40 
Green and red sandstones, charged with silicate of j iron, 5 
Liccenjigiliestieaih, wit neds. arene sandstone. 15 
Micaceous sandstone, containing Ditdoowhales Monidhaenss 
Third Trilobite } D. granulosa, &e., . 3 
bed. Alternations of green and Gtrigiocns shinabonils ee 20 
Micaceous sandstones, containing D. Meniskaensis, Xc., 2 
Thin layers of green sand, alternating with green cult; im- 
pregnated with silicate of iron, . 80 to 40 
Lower, brown siliceo-caleareous and ddlomitte hans of Nvaig: 
tain Island, and elsewhere, 4 
l Soft, thin-bedded sandstones, with sakes ote mica Renoeitedled. 10 to 15 
