CORRELATION OF NELSON RIVER LIMESTONE 349 



Lake Timiskaming region that so closely correspond in their lithology 

 and fauna to those of the late Middle Ordovician in the localities above 

 mentioned as to indicate that they also were laid down in the same prov- 

 ince of deposition. Schnchert^ has also reported a similar fauna from 

 the Frobisher Bay region in Baffin Land. 



It is thought that the late Middle Ordovician rocks in all of the above- 

 mentioned localities were laid down in the same great epi-continental sea 

 that advanced southward from the Arctic Ocean. 



The Galena limestone of the upper Mississippi Valley is thought to be 

 a nearly contemporaneous deposit with that of the Middle Ordovician 

 limestones in the localities above mentioned and probably was deposited 

 in an embayment of the same province. The Galena limestone lacks sev- 

 eral of the coral species that are common in the deposits of Middle Ordo- 

 vician age at the Hudson Bay and Lake Winnipeg localities. However, 

 among the more common fossils of the Galena are ReceptacuUtes oweni 

 and species representing the genera Hormotoma, Maclurina, and Trocho- 

 nema that are closely allied to species of these genera in the above list. 



ORDOVICIAN ROCKS EXPOSED ON SHAMMATTAWA RIVER 



No Paleozoic rocks are exposed in the banks of Hayes Eiver below the 

 mouth of the Shammattawa, but along the latter river outcrops of 'lime- 

 stone are encountered about 28 miles above its mouth, above which they 

 occur at intervals for a distance of about 15 miles. The rocks exposed 

 along this river are all included in the Shammattawa limestone, and are 

 considered to be about the age of the Maquoketa or Eichmond strata of 

 the Mississippi Valley. 



About 60 miles farther southeast, on a branch of Echoing Eiver, a 

 tributary of the Shammattawa, limestones corresponding in age to the 

 Nelson Eiver limestone above described, and containing similar fossils, 

 are exposed in low ledges at intervals for a distance of 5 to 8 miles. 



A detailed section of the limestone outcropping in the banks of Sham- 

 mattawa Eiver and lists of fossils collected from the several members are 

 given below: 



SECTION OF ROCKS EXPOSED ALONG SHAMMATTAWA RIVER 



Ordovician system 



Cincinnatian series 



Shammattawa limestone 



2. Limestone, yellowish brown, porous; dolomitie above, 

 mottled gray and brown below, forming the escarpment 



8 Charles Schuchert : Proc. U, S. Nat. Mus., vol. xxii, 1900, p. 149. 



