440 C. K. LEITH 



follows: (i) breccia or breccia-conglomerate, (2) graywacke shale or 

 slate, and (3) feldspathic sandstone or quartzite. The maximum thick- 

 ness of the first division is 600 feet; of the second, 100 feet; and of 

 the third, n 00 feet. Associated with these clastic rocks are various 

 rocks of igneous origin, including deep-seated diabase and gabbro and 

 volcanic ejectamenta. 



Comments. — The nature of the relations of the Huronian and 

 Laurentian rocks has so long been a subject of controversy and the 

 ground has been gone over so many times that comment seems unneces- 

 sary. But for readers who have not followed the controversy a state- 

 ment of one of the main points of contention may be of service. The 

 Laurentian rocks of Barlow and other Canadian geologists form the 

 basement upon which the Huronian rocks were deposited, and they also 

 have intrusive relations to the Huronian rocks. This anomaly is 

 explained by the fact that the granites and gneisses really form the 

 basement upon which the Huronian rocks were deposited, but that since 

 this deposition the granites and gneisses have been softened by fusion, 

 perhaps due to the weight of the overlying rocks, and that they now' 

 invade the lower portions of the Huronian rocks. 



Other geologists, particularly the United States geologists, have 

 maintained that no evidence has been adduced to show that there has 

 been any softening of the basement granites near their contact with the 

 overlying Huronian sediments ; that the granites and gneisses included 

 under the Laurentian by the Canadian geologists are of widely differ- 

 ent ages ; that they comprise both the original basement rocks, in their 

 original form, upon which the Huronian was deposited, and later rocks, 

 intrusive into both the Laurentian and Huronian ; and furthermore, 

 that in most regions it will be possible by close areal mapping to dis- 

 tinguish these different granites and gneisses. They would map the 

 basement granites and gneisses as one series, and separate from them 

 all later intrusives. 



Although Mr. Barlow has for many years maintained the total 

 absence of the normal erosion unconformity between the Laurentian 

 granite and the Huronian, he now reports the "discovery" of such a 

 contact near Lake Temiscaming. In finding a normal erosion uncon- 

 formity in this area he is many years behind Pumpelly, Irving, and 

 Van Hise, as indicated in a comment on a previous article of Mr. 

 Barlow. 1 It is thus now agreed that the original basement granites and 



j Jour. Geol., Vol. II, p. 419. 



