C. R. VAX [USE — HTJRONIAN VOLCANICS. 435 



The next two papers were read by the authors, being, on account of 

 their relationship, placed in juxtaposition: 



CKETACEOUS AND EARLY TERTIARY OF NORTHERN CALIFORNIA AND 



OREGON 



BY .!. S. DILLER 



This paper is printed as pages 205-224 of this volume. 



THE FAUNAS OF THE SHASTA AND CHICO FORMATIONS 



BY T. \V. STANTON 



This paper is printed as pages 245-256 of this volume. 



President Gilbert assumed the chair, and the following paper was read : 



THE HURONIAN VOLCANICS SOUTH OF LAKE SUPERIOR* 



BY C. R. VAN IIISE 



[Abstract] 



South of Lake Superior are extensive areas of Iluronian nicks, consisting of a 

 succession of basic lava flows, with iriterstratified contemporaneous fragmentals. 

 Associated with these are occasional porphyries. 



Petrographically the volcanic series includes porphyrite, augite-porphyrite, 

 amygdaloid, devitrified glass, flo wage breccia, and greenstone conglomerate. In- 

 cluded under the latter term are agglomerates, tuffs, mingled tuff and lava, and 

 true detrital conglomerates, the material of which is chiefly derived from the vol- 

 canic series. 



The porphyrites and augite-porphyrites are fine-grained, dense, and frequently 

 show, when weathered, a very curious spheroidal parting; also at times they pass 

 into flowage breccias. 



The amygdaloids vary from pumiceous or scoriaceous rocks into those in which 

 the amygdules are rare, until finally the porphyrites are reached. Like the porphy- 

 rites, they show at times a spheroidal parting or brecciation, and not infrequently 

 in the spheroidal phases, each of the spheroids is dense and noh-amygdaloidal on 

 one side and distinctly amygdaloidal upon the other. Moreover, the amygdal< tidal 

 portions are all on the upper sides of the blocks. It would seem licit while the 

 rock was still viscous it must have cracked, and that before solidification occurred, 

 in each block the amygdaloidal cavities rose to the upper part. 



The amygdules are chlorite, feldspar, epidote, and quartz, including chalcedony 

 and jasper. In the more open amygdaloids the amygdules are sometimes as much 

 as 8 or 10 inches in diameter. The ferruginous quartz, known as jasper in these 

 amygdaloids, is so remarkably like the jasper of the iron-hearing formation south of 

 Lake Superior that it was at first thought that these are inclusions caughl in the 

 lava, but a closer study shows their undoubted amygdaloidal character, since the 



♦ Published by permission of tic Director of the United 31 ilogiesil Survey. 



LXIV— Bull, Grot,. Soc. Am,, Vol, i L892. 



