52 



University of California. 



[Vol. 3. 



were also known as the Fundamental gneiss, the Grenville series 

 and the Norian series, respectively. 



To-day, no one qualified to speak upon the question enter- 

 tains the idea that the Fundamental gneiss or the anorthosites of 

 the Norian series are other than true igneous rocks. The Gren- 

 ville series, however, remains as Logan interpreted it, a strati- 

 graphic sequence of clearly recognizable clastic rocks, with 

 perhaps certain admixtures of igneous material. 



The term Huronian was first used by Logan and Hunt* in 

 1855 for the rocks of the north shore of Lake Huron and their 

 supposed equivalents on Lake Superior, now known as the 

 Keweenawau series. The rocks were at this time thought to be 

 probably of Cambrian age. In the work of the next few years, 

 the Upper Copper-bearing rocks of Lake Superior were segre- 

 gated from those on Lake Huron and the term Huronian retained 

 for the latter. In the report of 1863 the Huronian was described 

 and mapped as a clastic series of pre-Potsdam age, with certain 

 volcanic admixtures. Although it is probable, as I first sug- 

 gested,!" that the Huronian as described in the report of 1863 

 embraces more than one series of rocks, yet no one has ever 

 called in question the essentially clastic character of the great 

 bulk of the rocks so designated. 



Both of these terms, Laurentian and Huronian, signalized 

 most important discoveries in geological science. They were 

 immediately adopted and widely used both on this continent and 

 in Europe. The rocks comprised in these two series were re- 

 garded as of exceptional interest because they antedated the 

 Paleozoic and were separated from it by a profound and wide- 

 spread unconformity. This gave them a certain individuality as 

 a whole which it seemed desirable to recognize by the use of a 

 comprensive designation. Moreover, there might be other 

 pre- Cambrian series of clastic rocks resembling the Laurentian 

 or Huronian, the correlation of which with either of these series 

 might be very doubtful, and the 'progress of the science demanded 

 a comprehensive term which would not necessitate correlation of 

 its members in widely distant regions. These considerations 



*Sketeh of the Geology of Canada. Paris, 1855. 



1-Geol. and Nat. Hist. Survey of Canada, Ann. Rpt. 1885, p. 12CC. 



