« PROCEEDINGS OF THE PITTSBURG MEETING 



caldera, opposite Puu Eiiuhe. Behind it is Kaiholeua, 3,824 feet, the highest of 

 these buttes. Pun Eiiuhe has the altitude of 2,327 feet. 



All these elevations and the whole interior are covered by an abundant thick- 

 ness of volcanic ashes — apparently the same deposit with those I have described 

 in the paper cited above — and believed to have been ejected from Mokuaweoweo 

 in prehistoric times. 



There are streams of aa between Hilea and Honuapo which seem to have come 

 from the lower part of iVIohokea, but at a date subsequent to the formation of the 

 caldera and the deposition of the ashes. The more western flow is a mile and a 

 half in width. The more eastern flow starts from between two hills, just like the 

 other, but a mile away. The foreground of Button's view of the Hilea butte is a 

 field of aa. 



As this is the largest and most peculiar of all the Hawaiian calderas, it will arrest 

 the attention of travelers. Professor Alexander's map also shows another smaller 

 caldera, similarly situated, near Kapapala. 



Following Professor Hitchcock's paper, Dr I. C. White gave notice 

 relating to his proposed excursion up the Beaver river Wednesday 

 afternoon. 



The Society adjourned for the noon recess, and reconvened at 2.20 

 o'clock p m. The first paper of the afternoon session was 



ELLirSOIDA L STR UCTURE IN PRE-CAMBRIAN ROCKS OF LAKE SUPERIOR REGION 



BY J. MORGAN CLEMENTS 



[Abstract'] 



The greenstones of pre-Cambrian age in the Lake Superior region have very 

 commonly developed in them a structure which, since the masses separated by 

 this structure are ellipsoidal, is designated " ellipsoidal " structure. * 



A review of the ideas held by various observers concerning the origin of this 



structure is given, and it is concluded that it is an original structure, due to 



breaking up of a viscous lava while it was being extruded. The structure is 



shown to be of very widespread occurrence, especially so in the greenstones of the 



* Lake Superior region. 



The desirability of using the term "ellipsoidal," instead of "spheroidal," in 

 referring to this structure is urged in view of the fact that it is an original 

 structure, and that the bodies formed by this structure are ellipsoidal, whereas 

 the spheroidal structure in the rocks is of secondary nature, and is due to ex- 

 foliation caused by weathering. 



In discussion of the paper remarks were made by J. A. Holmes, U. S. 

 Grant, W. M. Davis, C. H. Hitchcock, and the author. 



* This structure was described and illustrated by means of the lantern slides. 



