MIDDLE AND UPPEE ORDOVICIAN. 171 



Ulrich states that the Upper Hudson shales, the Capfe Girardeau sandstone, 

 and the Lower Hudson shales of Keyes are now all regarded as of Richmond age. 



From Missouri these Ordovician strata cross the Mississippi into southern 

 Illinois, where they have very recently been critically studied by Savage,''"^ who 

 distinguishes "Galena-Trenton" light-colored crystalline nonmagnesian limestone, 

 68 to 80 feet; " Richmond-Maquoketa," 91 feet, consisting of a lower member of 

 sandstone or sandy shale (Thebes sandstone) and an upper one of bluish shale; and 

 Alexandrian, consisting of the Cape Girardeau limestone and certain overlying 

 beds, 41 feet. Savage proposed the new term "Alexandrian," from Alexander 

 County, 111., to designate a terrane which bridges "the lost interval between the 

 Cincinnatian and the Clinton." This terrane, previously distinguished by Ulrich 

 in the Mississippi Valley, appears to constitute a transition from Ordovician to 

 Silurian. Its correlation with Brazilian strata is discussed by Schuchert.'^^^ 



J 16. INDIANA. 



The strata and faunas of the Cincinnatian series in Indiajia have been described 

 in great detail by Cumings,"^ who has reclassified the sequence of limestone and 

 shale beds according to formations and- faunal zones. The divisions do not possess 

 very distinctive lithologic characters, all being Umestone, shaly limestone, or shale, 

 and they do not maintain a uniform character over any large area, as a rule. ♦ The 

 following is Cumings's classification,'^'^* as tabulated by him in comparison with 

 those that preceded : 



