T. E. Savage — Ordovician and Silurian Formations. 517 



presence of new Silurian types in the fauna is of much greater 

 significance than the lingering of a few Ordovician species. 

 Hence the formation is thought to represent early Silurian 

 time. 



Although the fauna of the Girardeau limestone shows 

 distinctly Silurian characters, it cannot be assigned to any 

 recognized horizon in the Clinton. The Sexton Creek beds, 

 which in this region succeed the Edgewood formation overly- 

 ing the Girardeau, are thought to represent a Clinton horizon as 

 low as any previously described. Hence it seems most condu- 

 cive to a clear statement of the facts to refer the Girardeau and 

 the succeeding Edgewood formation to a distinct time interval 

 earlier than the Clinton, called the Alexandrian, by which the 

 post-Richmond and pre-Clinton age of the beds, as shown 

 by their stratigraphic position and by the transitional character 

 of the faunas, is clearly indicated. 



The Post- Girardeau Unconformity. 



Clear evidence of an erosion interval succeeding the deposit 

 of the Girardeau limestone appears in an exposure in the bank 

 of the river three-fourths mile south of Gale. The strata here 

 which are next younger than the Girardeau limestone rest on 

 the very basal portion of this formation, three feet above the 

 top of the Orchard Creek shale. That a considerable thickness 

 of the Girardeau limestone was originally present here is 

 shown in the fact that at a distance of only twenty rods north 

 a thickness of thirteen feet of this limestone is exposed, and at 

 a less distance to the south a ledge, apparently in place, may 

 be seen in the river bank to a height of five and six feet. 



The Edgewood Limestone. 



The name Edgewood limestone is here applied to the strata 

 in this region lying above the Girardeau limestone and below 

 the Sexton Creek formation. In my paper of 1908 these are 

 referred to as beds 3b and 3c. The name is taken from the 

 town of Edgewood in Pike county, Missouri, near which place 

 occur strata that have furnished fossils of this horizon in great 

 abundance. In Alexander county the Edgewood beds are 

 exposed in the bank of the river three-fourths mile south of 

 Gale, where they occupy a channel eroded in the Girardeau 

 limestone. A thin band of this limestone may also be seen 

 in an abandoned quarry, one-fourth mile southeast of Gale. 

 At the former locality there is a conglomerate at the base, 

 composed of fragments of Girardeau limestone. This is suc- 

 ceeded by a few feet of fine-grained limestone, and dark, 

 calcareous shale. At the top is a massive layer of hard, gray, 



