66 INDEX TO THE SIEATIGRAPHY OF NORTH AMERICA. 



These objections were entirely just from the point of view of the systematic 

 geologist. The Keewatin does not belong to the Algonkian and is separated from 

 the lowest terrane of that system by an unconformity which is regarded as equiva- 

 lent to a long interval of time. But this interval and the distinction between these 

 terranes can not be expressed on the map so long as it is true, as stated by Dr. Adams, 

 that " It is impossible for us as yet to separate the Keewatin from the Huronian, 

 these two divisions having been, up to the present time, both classed as Huronian." 

 The legend of the map of 1906 does not, however, adequately express the fact that 

 the mapping is less advanced than investigation. It should have stated plainly that 

 eo- Algonkian comprised Lower and Middle Huronian, and that the areas so mapped 

 included some undifferentiated Keewatin which belongs to the Archean. 



In preparing the revised edition of the geologic map of North America, effective 

 agreement on problems of classification and nomenclature was sought by the oflScers 

 of the United States Siirvey. An international committee, composed of geologists 

 representing the surveys of Canada and the United States, had brought about an 

 understanding in regard to questions relating to the geology of the Lake Superior 

 region and to that of eastern Canada and New York. At a meeting of that commit- 

 tee in New York on December 29, 1906, it was voted that a subcommittee consisting 

 of three representatives from Canada and three from the United States be appointed 

 to consider questions of classification and nomenclature in connection with the 

 preparation of a geologic map of North America by the United States Geological 

 Survey. Bailey Willis was designated chairman of this subcommittee, the other 

 members to be selected later by correspondence between Messrs. Low and Hayes. 

 The subcommittee thus norninated consisted of F. D. Adams, R. A. Daly, and James 

 White, representing the Canadian Survey, and T. C. Chamberlin, C. R. Van Hise, 

 and Bailey Willis (chairman), for the United States Survey. A meeting was held 

 at Toronto March 7, 1907, and the entire scheme of nomenclature for the map was 

 considered from Quaternary to pre-Cambrian. The following classification of the 

 older rocks was agreed to : 



Paleozoic Cambrian and latest pre-Cambrian. 



p . I Later Proterozoic, including imseparated earlier Proterozoic. 

 1 Earlier Proterozoic, including unseparated later Proterozoic. 



Ancient schists and igneous rocks. 



Laurentian gneiss. 



The action of the committee was a compromise which was designed to meet the 

 needs of a legend for the general map but which did not go beyond that point in 

 attempting to adjust existing differences of opinion. Prof. Van Hise dissented from 

 the proposed division of the Proterozoic. The subcommittee did not indicate any 

 areas to be mapped under, any particular designation, that selection being left to 

 the compiler, Mr. Willis. 



From studies which followed the meeting at Toronto, the compiler concluded 

 that a map prepared on the compromise there reached would not adequately present 

 the known facts or express the existing uncertainties regarding the pre-Cambrian 

 sequence and classification. At his instance a further conference was proposed and 

 held at Chicago, February 21, 1908. The conferees were R. W. Brock, Acting 

 Director, and F. D. Adams, for the Canadian Survey; W. G. ,MiUer, for the Ontario 



