256 bulletin: museum of comparative zoology. 



It will be noted that in this section there is a formation added at 

 the top which is even younger than any found in Xew York and that 

 it is characterized by a fauna differing in a considerable number of 

 species from the fauna found below. The strata containing this 

 fauna are at the base, limestone, but above pass over into dark shale 

 which becomes finally typically "Utica" in faeies. The transition 

 from the limestone of the Picton into the limestone of the CoUingwood 

 is gradual and some of the species of the Picton continue into the 

 CoUingwood; there is probably no break in sedimentation. 



Minnesota. 



These formations, or at least most of them, can be traced across 



Ontario to the westward and in Minnesota the follo\\'ing section may 



be seen (Winchell and Ulrich, 121). 



Feet. 



8. Massive dolomitic limestone with Maclurites and ]Mac- 



lurina. Stewartville dolomite. 50 



7. Fine grained to subcrystalline limestone with some 

 argillaceous layers in the upper portion. Among the 

 fossils are Rafincsquina deltoidea, Zygospira uphami, 

 Fusispira nohilu, Fusispira inflata, Cyclospira bisulcata, 

 etc. 56 



6. Cherty limestone with Orfhis tricenaria, Cliiamhonites 

 americanus, Parastrophia hemiplicata, etc. Clitambon- 

 ites bed. 9 



0. Mostly thin-bedded limestone, argillaceous in the lower 

 portion and becoming more pure toward the top. 36 

 Zones 7 to 5 belong to the Prosser limestone. 



4. Blue shales with branching sponges. Fucoidbed. 6 



3. Blue shales with Bryozoa and Ostracoda. Phylloporina 



beds. ' ' 14 



2. Shales with limonite, sometimes oolitic in structure. 



Many Pelec\-poda. Ctenodonta bed. 9 



1. Dark green soft shale with numerous Bryozoa. Rhini- 



dictya bed. 23 



Zones 4 to 1 make up the Decorah shale. 

 There are two subdivisions of the Trenton strata in ^Minnesota 

 which may be correlated directly with formations in Ontario. These 

 -are the upper strata of the Prosser limestone, (zone 7 of the section 



