458 ALFRED C. LANE 



At the same time, one who accepts Chamberlin's planetesimal 

 theory must, I suppose, believe that all molten rocks have come 

 from fusion earlier or later. But that would apply to all igneous 

 rocks, and I do not see why it should involve a separate stratigraphic 

 treatment of any, and these Laurentian granites, instead of being 

 an immediately older formation, might be eras older. We find, 

 however, able geologists, represented on the committee, who hold 

 the subcrustal fusion theoiy probable or possible, and we find this 

 theory implied in previous use of some of the Lake Superior strati- 

 graphic terms; and I frankly own that I know of no conclusive 

 arguments against it. Any agreement we may make as to the use 

 of "Laurentian" is likely to be more or less of a compromise, and 

 the problem is so to define terms that their application should be as 

 far as possible the same, their extent represented by closely over- 

 lapping circles, whatever each man may privately think about the 

 true inwardness of the connection of the rocks thus grouped. 



The two terms the application of which we really had to delimit 

 were Logan's terms "Huronian" and "Laurentian," and we have 

 arrived at a temporory modus vivendi by using Lawson's " Keewatin"' 

 (Irving's "greenstone schists," Van Hise's "Mareniscan," Wads- 

 worth's "Cascade," Rominger's "Dioritic group") as a buffer state. 



One cannot fairly deny that Logan's idea of the Laurentian was 

 a purely stratigraphic one, since it was divided into an upper and 

 lower division, and that our proposed use of the term restricts it to 

 part of the lower part of the same only. But the fact is that Logan 

 founded the Laurentian and its divisions in eastern Canada. Then 

 he came to Lake Huron, and for very good reasons erected another 

 system, the Huronian, which in its most typical part is, we all agreed,, 

 younger than his Laurentian. So far we were led to the conventional 

 arrangement of Archean, divided into Huronian and Laurentian, 

 which one finds in most of the geological textbooks. 1 But, unfor- 

 tunately (as it seems to me), Logan included in his original Huronian 

 area a series of rocks, there relatively insignificant, green chloritic 

 schists (3 c of Logan), which the committee report calls the Thessalon 

 series. This series is, as we have said, intruded by granites, and it 

 seems to me that the rocks are stratigraphically as low and temporally 



1 Dana, Giekie, Lapparent, Credner, Kemp's Ore Deposits, etc. 



