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E. L. BRUCE 



accepted, it seems necessary to restrict those terms to the original 

 area in which they were appHed. If it seems convenient in any 

 other area to divide the rocks of this early period, local names 

 should be appHed to the divisions without implying any wide 

 regional correlation. Detailed examination may later make clear 

 the time relations of events; and if so, correlations can then be 

 made. If that ever becomes possible, it seems more than likely 

 that instead of rocks of similar lithology being found to belong 

 to the same period, it will be found that flows in some districts are 

 contemporaneous with sediments in others, or that a period of 

 deposition of sediments in one section corresponds to a period of 

 local erosion in a neighboring section. 



Although at present sufficient work has not been done to make 

 correlation possible, it is interesting to note the distribution of 

 the sediments in relation to the igneous rocks. In western Mani- 

 toba the sediments He above the flows. In north central Manitoba 

 flows and sediments are interbedded. In eastern Manitoba and 

 western Ontario the great mass of sediments lies beneath the 

 volcanics. In eastern Ontario the two are again interbedded. 

 These relations can be explained by the presence of a great area 

 of continental deposition extending southward from an old land 

 mass in central Canada in the very earhest times. Over this area, 

 terrestrial and shallow-water deposits were laid down on river 

 plains, piedmont fans, or deltas along whose margin sediments 

 were interbedded with subaqueous lava flows. Still farther out 

 no sediments at all were deposited until a later readjustment of 

 land and water shifted the zone of sedimentation to areas where, 

 previously, only igneous rocks were forming. At the same time 

 the central area became the site of igneous activity and the extrusion 

 of lavas over the clastic sediments already laid down. At present 

 this can be considered only a suggestion resting upon slight field 

 evidence. 



SUMMARY 



The points raised in the preceding discussion can be settled 

 only by more detailed work, but the following conclusions seem to 

 be warranted from present knowledge: 



