46 



S. K. CAI'I'S 



which, in this field at Icasl, j)r()vc(l of value in tletcrminin^ which 

 was the ui)i)er and which the lower side of a fjjiven flow as dei)Osited, 

 thus ;i.iding in decij>herin;^ the structure in a region where the normal 

 ;ittihidc of the beds had in many places been obscured, and where 

 ov( rhirnini^ of th(! bc^ds niif^ht be (!X()ected. 



'Ihc (!llij)soid;i,l greenstonc^s here; describ(;d were studied in the 

 vicinity of Ellamar, Alask;i, in the fall of m;i2, during ;ui investiga- 



I'k;. I. (^rojHH-Hfclion of lava flow, showing ellipsoidal forms. The ellipsoids 

 are charaelcrized by both radial aiul concentric scls of cracks. Pholo. by S. Paige. 



tion of the geology and mineral resources of the district by Mr. B. L. 

 Johnson and the writer. The exact age of the greenstones is not 

 known, but they are associated with a thick .series of sedimentary 

 beds which are believed to be for the most part of Mesozoic age. 

 '['he greenstones were of especial interest because all of the copper 

 deposits of the district are in the greenstone, or closely associated 

 with it. In those areas in which the greenstones are most highly 

 mineralized the lavas have been extc>nsively sheared and meta- 



