708 SCHUCHEET AND TWENHOFEL ORDOVICIC-SlLURIC SECTION 



base of the upper Medina. Beneath the last are the red marls of the 

 lower Medina. There can be no doubt that at all of these places we are 

 dealing with the basal beds of the upper Medina. 



From these statements it is seen that the upper Medina, which is now 

 commonly referred to as the typical Medina, includes beds that are clearly 

 Siluric, and in time not far removed from the Clinton. The Medina 

 fauna has three or four species that are seen only in the Becsie Eiver 

 formation, while some of the other forms first appear in the succeeding 

 beds. iSTevertheless, there is very little in common between the Medina 

 and the Becsie Eiver formation. Until the faunas of these four zones 

 have been completely studied a more detailed correlation can not be made. 

 It is thought, however, because of the absence of 8pirifer radiatus, Atrypa 

 reticularis, Dalmanella elegantula, and Encrinurus punctatus in the Bec- 

 sie Eiver formation, that it is older than the upper Medina. 



A somewhat similar fauna occurs in the Edgewood formation of Illi- 

 nois and Missouri.^^ So far as known, these species are Stromatopora, 

 Zaphrentis, Calapoecia canadensis, Lyellia thehesensis, Clathrodictyon 

 vesiculosum, Favosites cf. asper, Haly sites, TentacuUtes incurvus, Lingu- 

 lops, Dalmanella cf. meeki, OrtMs cf. callactis, Leptcena rliomhoidalis, 

 Rafinesquina mesacosta, Scliuchertella missouriensis , Rhyncliotrema cf. 

 incequivalvis, R. cf . dentata, R. janea, Rhynchotreta thehesensis, Triplecia 

 n. sp. (plicate type), Clorinda, Atrypa marginalis, A. putilla, Spirifer cf. 

 sulcatus, Hindella ( ?) hilling sana, Cypricardinia cf. arata, Conradella 

 cf. dyeri, Encrinurus, Proetus deter^minatus, Lichas clintonensis , and 

 Homalonotus. The time of this fauna may be that of the zones D^ to D4, 

 but it is evident that the source of this life is not that of the North 

 Atlantic, for genera are seen here unknown in the Becsie Eiver formation. 



Gun River formation {Richardson's Division D, excepting D^). — The 

 Gun Eiver formation, as exposed on the south shore, consists essentially 

 of ash gray to yellov»^ish white limestone (the bituminous limestones of 

 Eichardson, Geological Survey of Canada, 1857, page 301), usually in 

 thin beds inter stratified with bu.t little shale. Coral reefs are a marked 

 feature of the lower half of this formation, and with them intraforma- 

 tional conglomerates are often associated. Thin zones of conglomerate 

 consisting of small flat pebbles lying horizontally in a limestone matrix 

 are also common, particularly in the upper portion. The thickness of 

 the formation is about 400 feet. The strata on the south shore may be 

 seen from Saint Anns Cliff to within one mile of Jupiter Eiver. - Excel- 



" Schuchert : Journal of Geology, vol. 14, 1906, p. 728. 



