86 THE PENOKEE lUON UEAIMNG SERIES. 



original ourboiiatc, wliile others are redepositions of the dissolved iron in 

 new places, and the origin of still others is as yet nf>t understood; and 

 that, finally, the silicifying process began before the folding of these 

 formations, but continued afterwards. 



1887. 



Van PIiSE (C. I!.). Note on tlif EularfieiiK^it of Honilileudes and Auj>'ites in 

 Prag'niental and lirnptive Kofks. Am. Jonr. Sci., 3d series, vol. xxxiii, 1887, pp. 

 385-388. 



Prof. Van Hise, having previcaisly noted and described secitnd growths 

 on hornblendes in certain fragraental rocks of northern Minnesota, in this 

 paper describes similar enlargements which occur in certain eruptive green- 

 stones of the Penokee-Gogebic district. He shows that the secondary 

 hornblende lias in these greenstones attached itself at times to a uralitic 

 hornblende and at times to even an unaltered augite. Hornl)lende addi- 

 tions to hornblende crystals in erui)tive rocks had already been descril^ed 

 by Friedrich Becke. 



Ieving (R. D.). Is there a Huronian Group? Am. Jour. Sci., 3d series, vol. 

 XXXIV, 1887, pp. 204-216, 21!»-263, 365-.371. 



This paper, which was read before the National Academj- of Sciences 

 at Washington, D. C, April 22, 1887, presents at some considerable length 

 a series of arguments, obtained from all portions of the lake Superi(ir 

 region, tending to establish the genuineness of the Huronian group for 

 that region. The paper maintains the entire separateness of this group 

 from the underlying baseinent complex of gneiss, granite, and crystalline 

 schists and from the Keweenaw series above. It maintains also the title 

 of the Huronian to a rank equivalent with that of Cambrian, Silurian, 

 Devonian, etc., and argues that both Huronian and Keweenaw should be 

 admitted to the geological column with this rank, but that, since these 

 groups carr^s" no fossils, they cannot Ije directly coiTelated A^'ith pre- 

 Cambrian groups of geological provinces wholly distinct from that in 

 which they are found. The only correlation that can be safely made is that 

 of all of tlie clastic, groups collectively wliicli in any one region intervene 

 between the Cambrian and the ))as('mcnt crNstallines with any group or 



