KOMElS'CLATURE AND SUBDIVISION OF UPPER SILURIC 000 



20 species, of which the most significant are WiiitficldcUa ijrosscri Grabaii and 

 I'terutea lanii Grabaii. These are restricted to this liorizon, so far as known. 

 iipiroi-his laxus and numerous minute gastropods, besides plant remains, further 

 characterize this horizon. From tlie abundance of the brachiopod mentioned, 

 which is everywhere found and characteristic, the faunal zone is designated as 

 that of WhitfieMclla prosseri. 



II. THE MIDDLE MONROE 



This is represented in Michigan only by the Sylvania sandstone. This is 

 believed to repi-esent a long interval at the end of which a new series of fauuiie 

 invaded this region upon resubmergeuce. The thickness of the Sylvania seldom 

 exceeds 150 feet. 



III. THE UPPER MONROE 



Proposed name — Detroit River series.- — For this stratigraphic unit, the group 

 name Detroit River series is here proposed from the exposure of all its mem- 

 bers along that stream. It comprises four subdivisions or faunal zones. 



a. The Flat Roelc dolomites. — These are exposed at Flat Rock on the Huron 

 river, and are also found in the lower part of the salt shaft at Oakwood, 

 near Detroit. The fauna so far obtained is meager, comprising only the corals 

 Suvinpopora cooperi Grabau, 8. cf. iiisingeri Billings, and Favosites cf. iiiaxi- 

 iiiKS Troost. The first mentioned seems to be characteristic and restricted to 

 it, and the zone is provisionally called the Suringopora cooperi zone. The 

 thickness of the formation varies from 40 to 150 feet or more. 



&. The Anderdon limestone. — This name, suggested by the Reverend Thomas 

 Nattress, was adopted by Sherzer and Grabau for the coral reef limestone 

 exposed in the Anderdon quarry, Essex county, Ontario, two miles from Am- 

 herstburg, Ontario, and in the salt shaft at Oakwood, Detroit. Its thickness 

 is from 40 to 50 feet and its fauna a rich coral and stromatopora fauna. It 

 varies from a pure calcilutyte to a moderately coarse calcarenyte. Six species 

 of stromatoporoids and eleven of coral have been determined l)y Grabau. 

 Among the former Stylodicfyon sherzeri Grabau and Idiostroma nattressi 

 Grabau are characteristic and restricted. From the abundance of the latter 

 the faunal zone may be named the Idiostroma nattressi zone. Favosites of 

 Devonic affinities are characteristic. 



c. The Amltersthiiry "bed. — This name is proposed by Sherzer and Grabau 

 for the next higher stratum — a dolomite not over 20 feet thick and forming 

 a transition zone to the overlying Lucas. This zone, is rich in fossils, 52 spe- 

 cies having been identified by Grabau, most of them being new and of Devonic 

 afflnities. The fauna unites the Anderdon and Lucas elements to a certain 

 degree. Panenlca canadensis Whiteaves, though not absolutely restricted to it. 

 is its most characteristic fossil, and may serve to name the zone. The genus 

 Heliophrentis Grabau is further characteristic and distinctive, while Schuch- 

 ertella interstriata links it with the Bullhead (Akron) dolomite of western 

 New York, this and the Cobleskill being its eastern extension. Stropheo- 

 dontas of Devonic aspect further characterize the faunjTe. In common with 

 the Anderdon, it has an abundance of Conocardiiim monroense Grabau. 

 which is the zone fossil of the two foi-mations combined. The Spiriferoid 

 genus, Prosscrella Grabau, has species in the three upper members of the 

 Upper Monroe to which it is restricted (Prosserella liorizon). 



