_R. D. Irving — Is there a Huronian Group ? 369 



lar pre-Cambrian series outside of that geological province, we 

 can confidently enough, I think, correlate the geological inter- 

 val which holds these Lake Superior formations with that 

 which intervenes the world over between the Cambrian and 

 the great basement of genuine crystalline rocks, and which in 

 sever il regions includes great groups — sometimes one, some- 

 times more — of fragmental sedimentary strata. The progress 

 of geological discovery has been a downward one, and we may 

 look for the discovery of more fragmental groups than these, 

 and, I think, for the discovery of new faunae In any case, 

 whether our discoveries in this direction arc at an end or not, 

 some term — at least provisional in its application — covering the 

 great interval between the Cambrian and the Archaean, and 

 the clastic groups which have been or may be found lying in 

 this interval, would not only be a convenient addition to geo- 

 logical nomenclature, but would express a great truth which 

 the taxonomical system now generally in use entirely ignores. 



IX. In the foregoing pages I have shown that the Huronian 

 series is traceable throughout the Lake Superior Province, and 

 have presented a summary of facts which, as it seems to me, 

 establish its clastic and sedimentary nature, its great volume, 

 and its structural and chronological separate n ess from all other 

 rock groups. I may now turn back once more to the quota- 

 tion which serves as the text of this essay and see how far the 

 definition of a group there given is satisfied in the case of the 

 Huronian series; and, if there is any failure to satisfy this 

 definition in full, whether such failure should be allowed to 

 exclude this immense volume of strata from the group column, 

 and to compel the ignoring in geological chronology of the 

 immense lapse of time to which it must correspond. 



Analyzing the definition referred to, we find that it includes 

 the following distinct requirements; whose order, however, for 

 convenience of reference, I change from that given in the quo- 

 tation itself: — (1) All clastic formations, known to be such, 

 must be included within some group or other; (2) the group is 

 made up of sedimentary (mainly clastic) strata; (3) it includes 

 subordinate members genetically separate from one another; 

 that is, is made up of formations ; (4) it has a volume compar- 

 able with that of other recognized groups, such as the Cam- 

 brian, Silurian, Devonian, etc. ; (5) it is presumably world-wide 

 in distribution, being recognizable in various countries; (6) it 

 is defined mainly by paleontology, or "is admitted by all 

 geologists for motives in part arbitrary." 



The first of these conditions plainly compels us to place the 

 Huronian in some one of the already recognized groups, or to 

 make a new group for it, of which alternatives it has already 



