102 A. WINCHELL — A LAST WORD WITH THE HURONIAN. 



the actual juxtaposition was concealed by a bed of intercalated greenstone 

 or by low ground. Now the disturbances which affected the Huronian must 

 have affected similarly the underlying gneiss. If, therefore, the "upper 

 slate conglomerate " is discordant with the gneiss, it must have been dis- 

 cordant before the common disturbance; and if the "lower slate conglom- 

 erate " is conformable with the gneiss, it must have been so before the 

 disturbance. The " upper slate conglomerate " therefore, as a final infer- 

 ence, must have been unconformable with the " lower slate conglomerate." 

 We base this conclusion on the language of the founders, and not, at pres- 

 ent, on any evidence from personal observation. 



The facts here stated throw light on the mooted question of the conform- 

 ity or unconformity between the Huronian and the subjacent gneiss. Every 

 reader of Huronian literature has been puzzled by the numerous contradic- 

 tions of writers. These, when not the result of carelessness of statement, 

 are caused by the discordance of the upper and lower Huronian between 

 themselves. The lower Huronian is conformable with the gneiss ; the upper 

 Huronian unconformable. Wherever the upper Huronian extends beyond 

 the limits of the lower Huronian it rests unconformably on the gneiss. 

 This happens along the north shore of Lake Huron, where the upper slate 

 conglomerate rests on the gneiss. Farther south and west (on Ste. Marie 

 river) the upper slate conglomerate is itself wanting, and the white quartz- 

 ite rests immediately on the gneiss. On some of the islands in the North 

 channel (of Lake Huron) the quartzite, in turn, is wanting, and the Paleo- 

 zoic limestones rest on the gneiss. 



It appears that the Canadian writers, whatever they may have understood 

 about an "upper" and "lower" slate conglomerate, whenever they met a 

 slate conglomerate were in the habit of speaking of it as the slate conglom- 

 erate. If they noted discordances between the two they naturally attrib- 

 uted them to unequal local disturbances. It is not to be believed that they 

 would have failed to note the discordance and to inquire into its meaning if 

 their observations had extended into regions where each was found reposing 

 persistently in an attitude of discordance with the other. This theoretical 

 union of the two was all the easier in those parts of the territory where the 

 two were separated only by 150 feet of limestone. 



Evidence from Personal Observation. — To these inferences from the older 

 Canadian reports may be added the results of our own observations.* Every- 

 where along the coast between the Sault Ste. Marie and Blind river, wher- 

 ever the Huronian quartzites or schists are exposed to view, we find them, 

 as Logan states, with a low dip. The same is true along the Sault road 

 from Thessalon to the rear of the Bruce and Wellington mines. The same 

 is true along the valley of Thessalon river, by the turnpike, on both sides of 



*Some notes of a trip to this region by the writer and Professor N. H. Wincheli may be found in 

 16th Report of the Geol. Survey of Minnesota, 1887, pp. 13-40, 145-179. 



