THE BREAK IN THE HURONIAN 113 



alent of the unconformity between the upper and lower iron bearing 

 series of Michigan and Minnesota.* My own study of these rocks leads 

 me to the conclusion that this break is not of great significance. There 

 are pebbles of limestone in the upper slate conglomerate showing a cer- 

 tain interruption in the series, but the lower slate conglomerate (or gray- 

 wacke conglomerate) is very like the upper one and is not appreciably 

 more crystalline or schistose. Specimens from the basal conglomerate 

 east of Thessalon can be perfectly matched by specimens from the upper 

 conglomerate on Echo lake. It is much more probable that the real 

 break is beneath the basal conglomerate near Thessalon. It is likely 

 that some of the green schists found in the adjoining Laurentian are the 

 equivalents of the lower Keewatiri, west of lake Superior, and so repre- 

 sent the lower Huronian in the typical region. 



Much stress has properly been laid on this basal conglomerate by 

 Irving and Van Hise, and it will be well to discuss its bearing on the 

 Huronian question.f If the lower part of the typical Huronian series 

 corresponds to the Vermilion and other lower iron-bearing rocks of the 

 states to the west and south of lake Superior, it should contain an equiv- 

 alent for the characteristic jaspers interbedded with iron ore; but no 

 such rock has been found by Murray in his careful work when mapping 

 the region, nor by any later observers. On the 'other hand, jasper peb- 

 bles are found in greater or less numbers to the very bottom of the 

 series, a few occurring in the basal conglomerate itself. J If it be ad- 

 mitted that the large numbers of jasper pebbles, often with a banding- 

 suggesting sedimentation, are derived from a widespread sedimentary 

 rock, then sediments must have been formed on a large scale and have 

 been consoli4ated and rolled into pebbles before the basal conglomerate 

 was laid down. It is clear that this basal conglomerate is not the lowest 

 rock in the Algonkian, as defined by Van Hise in his excellent correla- 

 tion work, nor in the Huronian, as usually defined by Canadian geol- 

 ogists, but that a jasper bearing lower Algonkian or Huronian is to be 

 looked for somewhere as a source of its pebbles. 



On lake Temiscaming, at the northeastern end of the same great Huro- 

 nian area, another basal conglomerate has been described by Barlow and 

 Ferrier.§ The reasoning just given will apply to this conglomerate also, 

 for a few months ago Mr Archibald Blue and the writer found jasper 

 pebbles almost at the base of the Temiscaming conglomerate. In this 



* Van Hise, pre-Cambrian, p. 777 ; Alex. Winehell, Bull. Gleol. Soc. Am., vol. iv, 1893, p. 344, and 

 Am. Jour. Sci., vol. xlii, p. 317. 



fCf. Ont. Bur. Mines, 1899, part ii, p. 160, etcetera. 



X Ibid., p. 162. 



§ On the relations and structure of certain granites and associated arkose on Lake Temiscaming. 

 British Assoc, Toronto, 1897. 



