the St7 % uctural Relations of the Huronian. 227 



sharply. The granite of the ledge, the fragments of the 

 recomposed granite, and the great majority of those of the 

 conglomerate are of identical character. Although the actual 

 contact between the granite and conglomerate was not seen, 

 there can be no doubt that here was an old shore line and that 

 the granitic debris of this lower slate-conglomerate was derived 

 from the granite, this being a pre-existent ledge. A second 

 visit to this place was made by us in the company of Dr. 

 Charles Barrois, Dr. Hans Reusch, Dr. Carl Schmidt and Dr. 

 Th. Tschernyschew. After having carefully examined this 

 and another adjacent locality in which the relations were some- 

 what obscure, these gentlemen all agreed that the above is a 

 correct interpretation of the facts. 



This contact is not between the lowest formation of the 

 Original Huronian of Logan and Murray and their Lauren tian, 

 but is at the base of their lower slate-conglomerate, that is, is 

 below a member of the Lower Huronian series. When it is 

 considered that granitic rocks do not originate at the surface, 

 but must have been deeply denuded before they can yield 

 blocks to a basal conglomerate it may be considered a certainty 

 that at Garden River, there is a physical break of great magni- 

 tude between the Lower Huronian series and the basement 

 rocks of the region. 



Contact east of Thessalon. — A locality four or five miles 

 east of Thessalon visited by the late Prof. Irving and the 

 junior writer in 1883, and described by Prof. Irving in 1887,* 

 was again visited by the writers last summer. Prof. Irving states 

 that this place shows a true unconformity between the Huronian 

 and the Archean. He describes and figures a granitic and gneis- 

 sic basement complex upon which rests, with actual contact 

 exposed, a great conglomerate, the debris of which is derived 

 from the immediately subjacent rocks. While in 1883 the 

 basal conglomerate was seen on a magnificent scale, the contact 

 was found only for a few feet at the end of one island. 



At our recent visit to this locality the water of Lake Huron 

 was very low, at least three feet lower than in 1883. The con- 

 tact instead of being exposed only for a few feet at one place 

 was seen all the way across two low, dome-shaped glaciated 

 islands, the length of contact in each case being 40 or more 

 feet. The facts observed are as follows : 



The lowest rocks of this vicinity were found not to be 

 simply a granite or granitoid gneiss as might be inferred from 

 the general descriptions of Logan, but are an intricate mixture 

 of granites, granitoid gneisses or foliated granites, and various 



* Is there a Huronian Group? R. D. Irving: This Journal, III, 1887, vol. 

 xxxiv, pp. 207-216. 



