368 hall and sardeson — paleozoic formations of minnesota. 



Summary of the Stratigraphy. 



The following summary of thicknesses and leading lithological charac- 

 ters is given on the determinations of several authorities. The larger 

 number are from measurements and determinations by the writers. 



Devonian 



f Galena 



Lower 



Silurian. 



Upper 



( anibrian 



.Not subdivided limestone and shale . . 10- 



,-,. • • i Wykoff limestone 501 



uinclnnau \ Maquoketa shale and limestone .. 20 i 



Maclurea limestone 50 



TAngulasma.. .limestone 20 



( 'amarella. . . shaly limestone 30 



Orthisina calcareous shale 20 



Trenton [ Zygospira . . . .shale 8 



I Fucoid shale 20 



T . j Stictopora . . . .shale HO 



Sticloporella. .limestone and shale . 10 



Blue limestone 12 



Buff limestone 15 



Saint Peter. . Not subdivided sandstone 75- 



f Upper Shakopee dolomite 10- 



| Elevator B (Richmond I sandstone 



I Magnesian J Lower Shakopee dolomite 75- 



Jordan sandstone 75- 



Saint Lawrence dolomites and shales. 30- 



Feet. 



15 

 70 



120 



95 



164 

 65 



20 

 L75 

 21 II i 

 213 



[Potsdam . . . .Not subdivided sandstones and shales 0- 1,300 



Total thickness of Paleozoic strata in Minnesota 560- 2,437 



EXPLANATION OF PLATES 11 AND 12. 



Plate 11. — Paleozoic Rocks of Minnesota. 



Figure 1. — Basal conglomerate of the Potsdam at Taylors Falls ; the bowlders are 



diabase from contiguous masses of that rock. 

 Figure 2. — Contact of Trenton limestone and Saint Peter sandstone at Minneapolis 



in the gorge of the Mississippi river between the Washington avenue 



bridge and the State university campus. 



Plate 12. — Tnix Sections of Minnesota Paleozoic Rocks. 



Figure 1. — Dolomite, middle Magnesian, Hastings; rhombohedral character shown 



in a closely crystalline rock. X 70. 



Figun 2. — Dolomite, Magnesian series, Mankato; rhoinbohedra with granular cen- 

 ters and transparent rims. X 70. 



Figure 3. — Dolomite, Magnesian series, Frontenac old quarry; the arrangement of 

 infiltrated coloring matter produces a pseudo-oolitic structure. X 34. 



Figure 4. — Siliceous oolite, upper Shakopee (fragment found at ( Htawal ; centers of 

 spheres show enlargement of rounded quartz grains, i. < ., crystal frag- 

 ments with subsequent enlargement through deposition of micro- 

 crystalline silica. The lines show the direction of extinction. 



Figun 5. — From a shaly band in the buff limestone, Minneapolis ; under crossed 

 nicols to show rhombohedral outlines of the grains. 



Figun 6. — Maquoketa limestone, slightly magnified ; showing mottling character- 

 istic of the rock in typical Minnesota localities. 



