August 15, 1902.] 



SCIENCE. 



261 



monly developed in them a structure which, 

 since the masses separated by this struc- 

 ture are ellipsoidal, is designated ' ellip- 

 soidal ' structure. This structure was de- 

 scribed and illustrated by means of lantern 

 slides. 



A review of the ideas held by various 

 observers concerning the origin of this 

 structure was given, and the conclusion was 

 reached that the ' ellipsoidal ' was an orig- 

 inal structure due to the breaking up of 

 a viscous lava while it was being extruded. 

 The structure is of widespread occurrence, 

 especially in the greenstones of the Lake 

 Superior region. 



The desirability of using the term ' ellip- 

 soidal ' 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 struc- 

 ture in the rocks is of secondary nature 

 and is due to exfoliation caused by weather- 

 ing. 



Vermilion District of Minnesota: J. Mor- 

 gan Clements. 



The Vermilion district occurs in north- 

 eastern Minnesota, extending from Vermil- 

 ion lake, N. 70° E., to Gunflint lake on 

 the international boundary. As described 

 the district is about eighty miles long by 

 ten miles wide. The area surveyed com- 

 prises nearly 1,000 square miles. The 

 stratigraphic succession is as follows, given 

 in descending order: 



Pleistocene Glacial drift. 



( Unconformity ) . 



Keweenawan Great Gabbro and Lo- 

 gan sills. 

 (Unconformity) . 



Upper Huronian'^ 

 (Animikie series), i Upper slate formation. 

 Confined to eastern end | Gunflint formation 



of district J (iron-bearing) . 



( Unconformity ) . 



r Intrusives. 

 Knife slates. 

 Lower Huronian J Lower Huronian iron- 

 bearing formation. 

 (^ Ogishke conglomerate. 

 ( Unconformity ) . 



r Intrusive granites, por- 

 phyries and green- 

 Arcliean ( Vermilion J stones. 



series ) | Soudan formation 



(iron-bearing). 

 L Ely greenstone. 



The structure is complex. The Vermil- 

 ion district is broadly a great complex 

 synelinorium bounded on the north by the 

 Archean granite, and on the south by the 

 Huronian granite, Keweenawan gabbro, 

 with the Upper Huronian slates coming in 

 for a short distance. The ores are high- 

 grade hematites, averaging 63 per cent, of 

 iron and .05 per cent, of phosphorus, and 

 they are found in structural basins. Since 

 this district began to ship ore in 1884, it 

 has sent out some 17,000,000 tons of ore, 

 and the greater part of this came to Pitts- 

 burgh. 



As regards the origin of the iron, it ap- 

 pears to come first from preexisting rocks, 

 and then it is deposited to form the sedi- 

 mentary iron-bearing formations. In the 

 case of the Archean Soudan, the most eco- 

 nomically important iron-bearing forma- 

 tion of this region, the iron comes from the 

 Archean greenstone (basic and intermedi- 

 ate intrusives and volcanics). Later, after 

 the folding, the iron is leached from the 

 iron-bearing formation chiefly, and after 

 being carried down by descending meteoric 

 waters is precipitated as the oxide in places 

 favorable for its accumiTlation, thus form- 

 ing the ore deposits. 



The Pacific Mountain System of British 

 Columbia and Alaska: Arthur C. 

 Spencer. 



The author brought together and at- 

 tempted to interpret the existing descrip- 

 tions of the physiography of the coastwise 



