356 PALEOZOIC ROCKS OF THE HrDSO>- BAY REGIOX 



that in the exposure above described. Yirgiana decussata marks a defi- 

 nite zone near the base of the Silurian section (Stonewall Umestone) in 

 the yicinity of Grand Eapids. on the lower Saskatchewan EiTer, and it 

 donbtless marks a corresponding horizon of Silnrian on Xelson Eiver. 



Farther sonth. along the west side of Hndson and James bays. Silnrian 

 limestones are well exposed in the banks of the Severn. Winisk. Ekwan. 

 and Attawapiskat rivers. One of the most complete sections of the Silu- 

 rian ia the entire region outcrops along Severn Biver between 40 and 25 

 miles above its mouth. The succession of strata exposed along this stream 

 and their faunas are shown in the following detailed section : 



DETAILED >ECT:::' '17 iri?A7A EXPOSED ALOyG SETERy RIVER 



SilTirian system 



Niagaran series 



Attawapiskat coral reef ™*S?^ 



10. Limestone consisting of separate ridges or domes of 

 strnctnreless limestone composed of stromatoporoid 

 masses, corals, and other fossils, ranging from a few 

 to ICO or more feet in diameter and np to 30 or more 

 feet Mgli, with thinly and evenly bedded, fine-grained 

 limestone layers lapping up on the flanks of the 

 domes and ridges, from which they dip away at 

 angles of 20 to 30 degrees, but beoDme nearly hori- 

 zontal at a distance from them; exposed at Lime- 

 stone Island and at Long Portage, about 10 miles 

 farther down the river : containing the fossils listed 

 below : 75 to .S5 



Zaphrent^ patens. 



Zaphrentis stokesi. 



StromTjodes sp. 



Pucnosti/1us elegans. 



PaJeofavosites aspera. 



Favorites tuvosus. 



Fa/vo»it€8 cf. forbesi. 



Fa vosif^s h isingeH. 



Favosites sp. 



Luellia affinis. 



Heliolites sp. 



Fenestella suharctka. 



Stropheodonta sp. 



Stropheodonta philomela. 



Orthis aff. flaJjeUites. 



Pentamerus sp. 



Crupidula sp. 



Camarotcrchia sp. 



Atrupa cf. reticularis. 



Glassia variahUi^s. 



