SILURIC FAUNA FROM SOUTHERN MICHIGAN 545 



New York. A period of dry land is thus indicated for Michigan, Ohio, and 

 western New York and Canada, and elsewlaere as well, during which prolonged 

 erosion occurred, preceded by a basining of the Michigan and doming of the 

 Cincinnati regions, and the formation of the diagonal folds in southeastern 

 Michigan and Canada. It was during this same period of dry land condition 

 that the extensive brecciation of the Monroe beds occurred, through subierial 

 agencies, producing the large and small angular fragments, which were subse- 

 quently, on the advent of the mid-Devonic Dundee sea, incorporated in the base 

 of that formation, as now found at Mackinac island and Goderich, Canada, and 

 outlined by Grabau before this Society during a former meeting. 



Synopsis of the Faunas of the Monkoe Beds of Michigan, Ontario, Ohio, 



AND WESTERN NeW YORK 

 THE LOWER MONROE FAUNAS 



In general. — In the following annotated list all the species which have so 

 far been obtained from the Monroe formation are given. They are fully de- 

 scribed and illustrated in a memoir of this fauna (by Grabau), now awaiting 

 publication at the hands of the Michigan Geological Survey, and forming part 

 of an extensive discussion of the Monroe formation by the present authors. 

 Although the majority of species are new, and their full characterization can 

 not be given here, it is nevertheless deemed advisable to list them, with brief 

 suggestions of their affinities. 



Although the discussion of the Lower Monroe formation does not enter into 

 the present paper, it is nevertheless deemed desirable to include a list of the 

 faunae, since this will serve to emphasize the distinctness of the faunae of the 

 Upper Monroe beds. The subdivisions here used are those discussed in another 

 paper by Lane, Prosser, and the present authors, and adopted in the memoir 

 on the Monroe formation already referred to. 



A. Fauna of the Greenfield dolomite. — This horizon is so far known only 

 from Ohio, where it is exposed at Greenfield and Ballville. The fauna was 

 originally described by Whitfield, though many of his identifications can not 

 now be accepted. The type material is mostly in the collection of Columbia 

 University. 



Brachiopoda : 



1. Schucliertella hydraiilica (Whitfield), characterized by alternation of coarser 



with several finer radii ; very common. 



2. Camarotcrchia hydraiilica (Whitfield). 



fauna which fixes its ase, while immediately above these layers comes a limestone filled 

 with a rich Columbus fauna, thus making a clear case of it for central Ohio. 



"West of Toledo, however, the dividing line is not so evident between the lAicas dolo- 

 mite and the base of the Columbus limestone, as we consider it in northwestern Ohio. 

 "The following measurements are copied from my field book ; 



Columbus limestone 



Lucas dolomite 



Compact, drab dolomitic limestone, banded 63 feet 



Drab dolomitic limestone, with some gray or brown sand- 

 stone layers alternating .3G feet 



Sylvania sandstone 



"C. R. Staoffer, in discussion." 

 L — Bull. Geol. See. Am,. Vol. 19, 10O7 



