320 Lower Silurian of Wisconsin and Minnesota. 



ing from its fauna, a variety of Orthis suboequata Con., 0. dc- 

 Hecta Con., Rhynchonella orientalis Bill., Strophoniena niinneso- 

 tensis Winchell (varieties), Ambonychia attenuata Hall, etc. 



At Janesville, Wis., this bed is about eighteen feet in thick- 

 ness, in Jefferson county, Wis., about fourteen feet; in LaFayettc 

 Co., ten feet; at Dodgeville and Platteville, Wis., nearly twentr 

 feet. In Fillmore Co., Minnesota, it is about twelve feet; at 

 Rochester, Olmsted Co., the same; at Minneapolis, fifteen feet; 

 at Faribault, Rice Co., it is either represented by four and one- 

 half feet of green (apparently unfossiliferous) shale, or it is 

 absent. 



The ,second of the three limestone beds at Minneapolis 

 (seven feet of carbonaceous limestone) preserves few fossils 

 well. In nearly all other respects it is like the bed above rather 

 than the one below it. But I am not so sure that this is the case 

 elsewhere. At Faribault the seven feet immediately on the green 

 shale mentioned above has characteristics of this bed. In south- 

 eastern Minnesota it is less easily distinguishable from the bed be- 

 low. In southwestern Wisconsin I could not find it at all, unless 

 it is there more fossiliferous, and hence confused w4th the strata 

 above. But at other points in Wisconsin, these strata seem to be 

 distinguishable though in every case less distinctly than at Min- 

 neapolis. 



The five feet three inches at the top of the limestone at Min- 

 neapolis is the fossiliferous bed of the three. The species that 

 occur in it are essentially the same forms as those common in the 

 Lower Blue bed of W^isconsin. Orthis perveta Con., Trochoncnia 

 beloiten^e Whitf., Cypricardites rectirostris H., are abundant 

 forms. 



At Faribault this bed is of about the usual depth for Minne- 

 sota, but is darker and more carbonaceous than usual and brachio- 

 pod shells are well preserved. In Wisconsin, at Platteville, Min- 

 eral Point and Dodgeville, it seemed to be from ten to fifteen feet 

 thick and perhaps the same thickness at Janesville. 



The rest of the Lower Trenton in ^Minnesota is shale which is 

 supposed to be mainly the equivalent of the L^pper Buff and 

 Upper Blue limestone of Wisconsin. But the lithological differ- 

 ences, together with the scarcity of fauna in Wisconsin make this 

 more difficult to decide. All the evidence met with, however, is 

 in favor of the supposition that the lower Trenton shales in Min- 



