December 17, 1915] 



SCIENCE 



869 



tion, has accepted the position as head of the 

 department of botany and plant pathology in 

 the N'orth Carolina Agricultural and Mechan- 

 ical College, "West Ealeigh, N. C. He will 

 enter upon his new duties on January 1. 



Arthur S. Ehoads, who has a bachelor's and 

 master's degree in science from the Pennsyl- 

 vania State College, has recently taken a posi- 

 tion as assistant in forest pathology in the 

 New York College of Forestry. 



Dr. E. "W. a. Walker, fellow of IJniversity 

 College, Oxford, has been appointed lecturer 

 in pathology. 



DISCUSSION AND COBBESPONDENCE 

 pre-cambrian nomenclature 



To THE Editor of Science : The State Geo- 

 logical Reports often contain facts which are 

 of wide interest but which are liable to be over- 

 looked. As all general conclusions must de- 

 pend on local facts, it seems to me to be the. 

 duty of those who recognize the wide bearing 

 of these local facts to bring them to public 

 notice. I have just received a book^ in which 

 the results of the " Contributions to Pre-Cam- 

 brian Geology" by R. C. Allen, affect not 

 merely Michigan, but the whole subject of Pre- 

 Cambrian nomenclature. Eor instance the 

 very interesting and valuable tables published 

 by Miller and Knight showing the correlation 

 of Pre-Cambrian rocks^ might be revised by 

 the authors in view of this publication. 



Now the main point is this: Andrew 0. 

 Lawson in his study of the pre-Cambrian rocks 

 urges that the Animikie, which has always 

 been considered a part of the Huronian pe- 

 riod, is a period independent of, and later 

 than the Huronian period. The author, 

 R. C. Allen, shows good reason to believe 

 that the Gogebic which has always been corre- 

 lated with the Animikie should be corre- 

 lated with the middle Huronian. He ac- 

 cordingly correlates the Animikie as middle 

 Huronian. This seems to me to be worthy of 



1 Pub. 18, Geo!. Series 15, Mich. Geol. and Biol. 

 Sur7., by Allen and Barrett. 



2 P.-O. Geol. of SE. Ont., by Miller and Knight, 

 Eep. Bureau of Mines, Vol. XXII. 



mention in as much as Allen has not confined 

 himself to work in Michigan but has worked in 

 the original Animikie region. I first met him 

 there. 



Now, in view of these facts, I may put in 

 print suspicions which I have only breathed in 

 conversation, namely, that in the original 

 Huronian where there are bright bits of jasper 

 in the Thessalon conglomerate, they were de- 

 rived from a middle iron-bearing series which 

 is not well represented in that area. In view 

 of the facts brought forward by Allen which 

 indicate that the Gogebic was invaded by gran- 

 ite intrusions, and then later was overlaid un- 

 conformably by another formation, the Copps 

 formation, it seems to me it would be very 

 premature to make the changes suggested by 

 Lawson or by Miller and Knight. I have no 

 doubt the facts presented in this report will 

 have to be carefully scrutinized by these 

 writers, who will im.doubtedly form their own 

 conclusions. 



In the meantime we must be very careful . 

 about trying to make widespread pre-Cambrian 

 subdivisions. In any one district the division 

 line between those strata affected by granite 

 intrusions and metamorphosis and those not so 

 affected is marked, and such was practically the 

 line between the Huronian and Lam-entian as 

 originally mapped. But it becomes more and 

 more clear that granite intrusions on a large 

 scale have taken place in different regions at 

 different dates. And it is very doubtful to me 

 whether the habit of grouping granite intru- 

 sions under names which are more or less cor- 

 related with inter-geologic periods is a wise 

 arrangement. 



The same report contains a valuable paper 

 by Case and Robinson which emphasizes and 

 shows the correctness of the downward salients 

 of Schucliert's curve showing the extent of the 

 ocean in those times in the paleozoic section in 

 Michigan. Wliat we need to do for the pre- 

 Cambrian is to adopt the same laborious proc- 

 ess that Schuchert has completed and see if 

 possibly different types of strata, such as the 

 great Middle Huronian (Mio-Huronian) iron- 

 bearing formation may not, as I have sug- 

 gested, correlate with definite stages in the 



