356 T. E. SAVAGE ALEXANDRIAN SERIES IN MISSOURI AND ILLINOIS 



break. The Silurian aspect of the fauna of the Girardeau limestone was 

 emphasized, and the name Alexandrian series was proposed to embrace 

 these post-Cincinnatian and pre-Clinton beds represented by the Girar- 

 deau limestone and the succeeding strata lying below the equivalent of 

 the Brassfield limestone. 



The following year the name Sexton Creek limestone was defined 18 for 

 the Silurian strata in Illinois that are equivalent to some part of the 

 Brassfield. The term Edgewood limestone was at the same time applied 

 to that part of the Alexandrian series in western Illinois and eastern 

 Missouri lying between the Girardeau and the Sexton Creek limestones. 



In discussing the "Faunal succession and the correlation of the pre- 

 Devonian formations of southern Illinois" 19 in 1910, the significance of 

 the Silurian types of fossils in the Girardeau limestone was pointed out, 

 and the Channahon limestone, in Will County, was regarded as the 

 equivalent of some part of the Edgewood formation of southern Illinois 

 and eastern Missouri. 



In a paper read- at the 1911 meeting of the Illinois Academy of Sci- 

 ence, the Essex limestone, 20 in Kankakee County, was described and the 

 formation was provisionally referred to the Alexandrian series above the 

 Edgewood and below the Sexton Creek limestone. 



General stratigraphic Belations 



The strata comprising the Alexandrian series in Illinois and Missouri 

 are everywhere unconformable on some horizon of the Bichmond, and 

 they are separated by a similar sedimentary break from the rocks that 

 lie above them. 



In the south part of the area, in Alexander and Union counties, Illi- 

 nois, and Cape Girardeau County, Missouri, these strata rest on different 

 levels of the Orchard Creek shale of Bichmond age, and are followed by 

 Helderbergian limestone having the faunal aspect of the JSTew Scotland 

 of New York. 



Farther north, in Jersey, Calhoun, and Pike counties, Illinois, and 

 Lincoln, Pike, and Balls counties, Missouri, the Alexandrian overlies a 

 blue shale that in Illinois has been correlated with the Maquoketa, and 

 in Missouri has been called Hudson Biver shale and Buffalo Creek shale, 

 the upper part of which corresponds to the Orchard Creek shale of south- 



18 T. E. Savage : The Ordovician and Silurian formations in Alexander county, Illinois. 

 Am. Jour. Sci., vol. xxviii, December, 1909, pp. 509-519. 



19 T. E. Savage : Illinois State Geological Survey. Bull. No. 16, 1910, pp. 302-341. 



20 T. E. Savage : The Channahon and Essex limestones in Illinois. Trans. Illinois Acad. 

 Sci., vol. iv, 1912, pp. 97-103. 



