248 INDEX TO THE STRATIGRAPHY OF .NORTH AMERICA. 



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 by Grabau. Among the former Stylodictyon 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) Amhersiburg 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 species having been identified by Grabau, most of them being 

 new and of Devonic affinities. The fauna unites the Anderdon and Lucas elements to a certain 

 degree. Panenka canadensis Whiteaves, though not absolutely restricted to it, is its most 

 characteristic fossil and may serve to name the zone. The genus Hehophrentis Grabau is 

 further characteristic and distinctive, while SchucherteUa interstriata links it with the Bullhead 

 (Akron) dolomite of western New York, this and the CobleskUl being its eastern extension. 

 Stropheodontas of Devonic aspect further characterize the faunas. In common with the Ander- 

 don, it has an abundance of Conocardium monroense Grabau, which is the zone fossil of the two 

 formations combined. The spiriferoid genus Prosserella Grabau has species in the three upper 

 members of the Upper Monroe to which it is restricted (Prosserella horizon). 



(d) Lucas dolomite. — This name was proposed by Prosser in 1903 for the upper dolomites 

 so well exposed in Lucas County, Ohio. Here they mostly rest directly on the Sylvania, the 

 other beds being cut out by overlap. The fauna is rich and pecuHar, European types of gas- 

 tropods predominating. The genus Acanthonema Grabau, though represented in the Amherst- 

 burg, is most characteristic, and the faunal zone may be designated the Acanthonema zone. 

 Its thickness varies up to 200 feet or over. CylindroJielium profundum is restricted to it and 

 may be regarded as another good zone fossil. 



The proposed classification of these authors in tabular form is as follows : 



Upper Monroe or Detroit River series (L., P., S., and G.); zone of Prosserella: 



(d) Lucas dolomite (Prosser). (Zone of Cylindrohelium profundum and Acanthonema.) 



(c) Amherstburg dolomite (Sherzer and Grabau). (Zone of Panenka canadensis.) 

 (6) Anderdon limestone (Nattress). {Zone oildiostroma nattressi.) 



(a) Flat Rock dolomite (Lane, Prosser, Sherzer, and Grabau). Zone of Syringopora eooperi. 

 Disconformity. 



Middle Monroe: Sylvania sandstone. 



Disconformity. 



Lower Monroe or Bass Islands series (L., P., S., and G.); zone of Leperditia: 



(d) Raisin River dolomite (Lane, Prosser, Sherzer, and Grabau). (Zone of Whitfieldella prosseri.) 

 (c) Put-in Bay dolomite (Lane, Prosser, Sherzer, and Grabau). (Zone of Goniophora dubia). 



(b) Tymochtee beds (N. H. Winctell). 



{a) Greenfield dolomite (Grabau). (Zone of Schuchertella hydraulica.) 



The characteristic faunas of the above-named divisions are listed by Sherzer 

 and Grabau in a preliminary article ^^^ and appear with full descriptions in a report 

 published by the Michigan Survey .^^^ The authors deduce from the faunas and 

 stratigraphic relations three interruptions in the process of sedimentation, or "dis- 

 conformities," and comment on the relations as follows: ^^** 



A survey of these faunas brings out the remarkable fact that there is nothing in common 

 (a few doubtfully identified gastropods excepted) between the Lower and Upper Monroe. So 

 distinct are the faunas that they may be considered as derived from widely separated provinces. 

 The Lower Monroe is apparently an Atlantic fauna or series of faunas, and we are led to believe 

 that an embayment from the Atlantic extended as far as Wisconsin in post-Salina time and 

 that the successive members of the Lower Monroe were deposited in this. The marine "Salina" 

 described by Schuchert from Maryland most probably belongs here, the path of invasion being 

 approximately across that region. There appears to be nothing in New York which corresponds 



