25-i C. Keyes — Affinities of t/u Alexandrian Series. 



Art. XVIII. — Paleogeographical Affinities of the Alexan- 

 drian Series ; by Charles Keyes. 



No more illuminating example exists emphasizing the urgent 

 need of directly applying the broader paleogeographical prin- 

 ciples to the solution of local problems in stratigraphy than that 

 presented b} 7 recent attempts to deliminate sundry taxonomic 

 groups of terranes in the continental interior. 



For several reasons the Silurian section of northeast Mis- 

 souri, for instance, is particularly instructive.* The sequence 

 is so meagerly represented that it is all comprised within the 

 vertical limits of barely a score of feet. The succession is 

 divided medially by a marked plane of unconformity. There 

 is, as we now know, an overlapping of a southern earlier Silu- 

 rian deposition by a later northern Silurian formation. The 

 special stratigraphic significance of these facts have a far-reach- 

 ing bearing ; and certain aspects may be briefly considered. 



The section of the rocks in question and their immediate 

 associations as displayed in the deep valley of Noix creek and 

 elsewhere in the vicinity of Louisiana, in Pike County, Missouri, 

 is essentially as follows : 



Silurian Section in Northeast Missouri. 



7. Louisiana limestone 50 feet 



6. Saverton shales (green) 50 



5. Grassy (black) shales (Carboniferous) . 60 



Unconformity. 

 4. Limestone, brown to reddish, heavily bedded 



(Devonian) 10 



Unconformity. 

 3. Limestone, buff, massive (Bowling Green, Silurian) 20 



TTnconform ity. 

 2. Limestone, brown, thinly bedded, locally oolitic 



(JVoix limestone, Silurian) ?.. 10 



Unconform ity. 

 1. Shales, blue (Ordovician) 60 



In this section Nos. 2 and 3 constitute the Edgewood for- 

 mation of Savage.f The non-oolitic portion of the first named 

 member is, by the same author, termed the Cyrene limestone.;}: 

 Farther south, in southeast Missouri, is the Girardeau lime- 

 stone. Together these three beds, and some others in north- 

 eastern Illinois, are grouped into the Alexandrian series,§ 



* Missouri Geol. Surv., vol. iv, p. 47, 1894. 

 fThis Journal, (4), vol. xxviii, p. 517, 1909. 

 X Bull. Geol. Soc. America, vol. xxiv, p. 361, 1918. 

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



