JR. D. Irving — Is there a Huronian Group f 371 



besides which it is separated from adjacent rocks by tremen- 

 dous unconformities, representative of immense lapses of time, 

 while in many cases the later fossiliferous groups are divided 

 from one another by no sharp structural or even paleonto- 

 logical line. Now similar arguments would establish the 

 group rank also of the Keweenaw series. These two groups 

 represent a great lapse of time hitherto ignored. They belong 

 to that great gap — which they only partially fill — lying be- 

 tween the Cambrian and the Archsean, as do also other rock 

 groups in other portions of the world. 



As now generally accepted and presented in the books, the 

 geological column makes no provision whatever for these great 

 intermediate groups of strata; nor is there any uniformity of 

 practice as to their classification among those geologists who 

 have written upon them. Even among those who believe in its 

 complete structural separateness from the upper Cambrian strata 

 the Keweenaw series has been classified now as the upper por- 

 tion of the Archsean, now as the lower portion of the Cambrian. 

 The Huronian when first recognized by the Canadian Survey 

 was put in the Cambrian ; later the same survey threw it into 

 the Archaean. In the same way the immense succession of 

 rocks which lies below the great unconformity of the depths of 

 the Grand Canon of the Colorado has been classed now as 

 Cambrian, again as Archsean. But all of these groups are 

 plainly wholly separate in point of time of production from 

 both the Cambrian above and the Archsean below, each of 

 them being fully entitled to a classificatory value equal to that 

 of Cambrian, Silurian, etc. It seems evident, then, that they 

 should receive admission, as entirely separate groups, to the 

 geological column. But their admission to this column appears 

 to involve a difficulty, and also a further important modification 

 of the column. As has already been fully admitted, we cannot 

 speak, certainly in the present stage of the science, of Huronian 

 rocks in portions of the world remote from the Lake Superior 

 Province. In other words, we cannot correlate directly with 

 the Huronian any pre-Cambrian fragmentals elsewhere found, 

 since such fragmentals might, so far as we are able to deter- 

 mine, be rather the equivalents of the Keweenawan or of some 

 series belonging in the gap above the Keweenawan, in that 

 below it, or again in that below the Huronian. We must, 

 therefore, in constructing our column, in some way indicate 

 that these groups have individually a recognizable extent 

 which is as yet only local. But plainly some term is necessary 

 to cover all of these groups collectively; in other words, all of 

 that great gap which lies between the base of the Cambrian 

 and the summit of the Archaean gneissic and schistose base- 

 ment. This name cannot be one of the group rank, since it 



