340 PA^LEOZOIC ROCKS OF THE HUDSON BAY REGION 



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Detailed section of Devonian strata exposed along Abitibi River 373 



Correlation of Devonian strata exposed along Abitibi River 375 



Sextant sandstone and shale 375 



Abitibi River limestone 375 



Long Rapids shale 377 



Introduction 



The explorations of several geologists have contributed to our knowl- 

 edge of the Paleozoic rocks of the Hudson Bay region, among whom the 

 names of Bell, Tyrrell, Mclnness, and Parks will always be associated in 

 an important way with the geology of this region. These men have shown 

 that Ordovician, Silurian, and Devonian strata are represented in the 

 great sedimentary outlier lying west and south of Hudson and James 

 bays. However, the succession and detailed sections of the formations 

 had not been made out, and it had not been determined in all cases what 

 horizons of these systems were present in the region, nor was it certain 

 that all of the formations there present had been recognized. 



From the standpoint of paleogeography and historical geology, it is 

 highly desirable that the definite and complete sequence of -the Paleozoic 

 formations and their faunas in this region should be determined, as from 

 these could be established what northern sea connections existed during 

 the deposition of corresponding deposits in other parts of the continent. 

 Such a systematic study of the stratigraphy of this region was recently 

 made possible by a grant from the Graduate School of the University of 

 Illinois, and an expedition to the region was made by the writers during 

 the summer of 1916. 



It was known in general that the Ordovician strata were present far- 

 thest north in this region, and that younger Silurian and Devonian beds 

 bordered the bay successively farther south. The distribution of the rocks 

 of the various systems suggested that the strata dipped toward the bay at 

 a rate somewhat greater than the fall of the streams, and that along the 

 rivers the older rocks were exposed farthest west and successively younger 

 strata would be encountered farther east toward the bay. It was thought 

 that by making as detailed sections and as full collections of fossils as 

 possible across the belt of each system on at least two or three rivers, and 

 combining these sections, a rather complete succession of the rocks present 

 would be obtained. On account of the low, swampy character of the inter- 

 stream areas and the thick accumulations of peat and moss that generally 

 cover the surface, the rock exposures are practically confined to the banks 

 of the larger streams which, almost without exception, flow across the belt 



