C. If eyes — Affinities of the Alexandrian Series. 255 



which is regarded of Early Silurian age. The Silurian strata 

 of northwestern Illinois and northeastern Iowa appear to be of 

 younger age. 



When, several years ago, the principal Mississippian section " 

 was described by me, the Silurian beds of the Louisiana district 

 (Missouri) came in for incidental consideration only. The 

 brown limestone (Bowling Green) was chiefly taken into ac- 

 count, since the oolite was regarded as merely a local and quite 

 unimportant facies. In referring it to the Niagara horizon of 

 the Iowa sectionf the lithology and lithologic sequence had to 

 be mainly relied upon in correlation, because of the fact of an 

 absence of fossils in it, and because there were present in the 

 associated oolite many typical Silurian forms. Although evi- 

 dences of unconformable relationships were noted at the time, it 

 was not until several years later that the full significance of this 

 feature was grasped. 



Approaching the problem from a different direction, Savage;}: 

 supplies us with very complete and valuable data for its correct 

 solution ; but he also gives as little attention to the significance 

 of the massive upper member as was formerly attached to the 

 lower oolitic layer. In consequence this author is induced to 

 throw the entire Silurian section of the Pike County region into 

 a single group — the Edgewood formation, and to parallel this 

 terrane with that part of the section of southeastern Missouri 

 above the Girardeau limestone, calling the whole sequence the 

 Alexandrian series. 



In the proposal of the term Edgewood formation for the 

 three beds — the Bowling Green limestone, the Noix oolite, or 

 local phase of the member later called the Noix limestone by 

 Ulrich,§ and the lower normal limestone to which the title 

 Cyrene was given — the existence of the notable plane of 

 unconformity at the base of the Bowling Green limestone was 

 entirely overlooked. It now transpires that the stratigraphic 

 affinities of the last mentioned formation are with the more 

 northern, or Iowa, section, instead of the more southern, or 

 southern Missouri, section ; and that its true relations are with 

 Mid-Silurian rather than with Early Silurian terranes. In con- 

 sequence of these facts Edgewood Formation as a terranal 

 designation becomes at once invalidated. By slight change in 

 the original signification the term Noix, as applied to a lime- 

 stone member, assumes a useful and valid role. The appella- 

 tion Cyrene limestone also becomes unnecessary. 



Notwithstanding the fact that as originally proposed | Alex- 

 andrian series is manifestly intended to include strata belongs- 



* Bull. Geol. Soc. America, vol. iii, p. 286, 1892. 

 + This Journal, (3), vol. xliv, p. 448, 1892. 

 JBull. Geol. Soc. America, vol. xxiv, p. 351, 1913. 

 § Bull. Geol. Soc. America, vol. xxii, p. 608, 1911. 

 1 This Journal (4), vol. xxv, p. 434, 1908. 



