176 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Blackwelder **° showed that the quartzite in Ogden Canyon is a Cambrian 

 quartzite which owes its apparent stratigraphic position to an overthrust. There is 

 therefore no Ordovician quartzite in Ogden Canyon and the name is inappropriate. 

 But an Ordovician quartzite does occur in Cache Valley and also south of Ogden. 

 In green shales at the base of this quartzite have been found abundant fossils, 

 which, on preliminary examination, E. O. Uh-ich ^^ pronounces to be of the age 

 of the Beekmantown fauna of the Eastern States. 



K 13. BLACK HILLS. 



In the northern Black Hills occurs a formation similar to the massive Bighorn 

 dolomite, known as the White wood limestone, which is of Trenton, age. It is 

 80 feet thick near Deadwood, but thins out toward the south.^*^*' *^^ 



In the Front, ranges of Colorado north of Colorado Springs the Ordovician, 

 like other pre-Carboniferous Paleozoic systems, is lacking. 



K 16. SOUTHEASTERN WISCONSIN AND NORTHEASTERN ILLINOIS. 



The St. Peter sandstone, Trenton limestone (as defined by the Wisconsin 

 Geological and Natural History Survey), Galena dolomite, and "Cincinnati" 

 shale constitute the Ordovician of Wisconsin and northeastern Illinois above the 

 "Lower Magnesian" ("Calciferous") limestone. The St. Peter" is a friable 

 white or yellow sandstone, which varies in thickness from a thin edge to 212 feet 

 and lies unconformably on the "Lower Magnesian." The overlying Trenton is 

 in part a simple, in part a magnesian limestone with clayey partings, about 115 

 feet thick, in which several distinct subdivisions are recognized. Next higher is 

 the Galena, a coarse-grained thick-bedded dolomite, about 250 feet thick, which 

 becomes more argillaceous toward the northeast and northwest. The highest 

 formation of the Ordovician section is the "Cincinnati" shale, bluish or greenish, 

 with intercalated limestones, which reaches a thickness of 200 feet or more.^^'" 

 A period of nondeposition and erosion followed in Wisconsin and elsewhere in the 

 central western United States ^*® covering late Ordovician time. This period of 

 nondeposition corresponds to the interval between the "Cincinnati" shale and 

 the Galena dolomite. The so-called "Cincinnati" shale is of Richmond age. In 

 southwestern Wisconsin and northwestern Illinois the Ordovician shale outcrops 

 and is there known as Maquoketa shale. 



The formations in northern Illinois constitute the southward extension of 

 those described by Chamberlin'for Wisconsin. Bain" has recently described the 

 limestones and associated strata of northwestern Illinois. Above the earlier 

 Ordovician rocks he recognizes the St. Peter sandstone, PlatteviUe ("Trenton") 

 limestone. Galena limestone, and Maquoketa shale. 



K 17-18. PENNSYLVANIA AND NEW JERSEY. 



The limestones of southeastern Pennsylvania have been described by Stose.*"^ 

 The quotations regarding the Cambrian and early Ordovician formations given in 

 Chapter III (pp. 107-113) are here continued for the later Ordovician. 



The Stones River limestone is composed in general of three divisions — a middle 

 band of massive pure granular limestone containing the large gastropod Maclurea 



