ABSTRACT8 OF PAPERS READ JANUARY 2 555 



gests that the structure of the area, while intricate in details, is rather simple in 

 its broader lines, and indicates that the extremely complicated structure inferred 

 by earlier workers is not corroborated by the later and more detailed investigations. 

 It includes a brief discussion of the probable age of the deposits, and susfgests that 

 this is Paleozoic and not pre-Cambrian, as formerly supposed, for almost if noi all 

 the gneisses. 



The paper is published in full in the American Journal of Science, 

 fourth series, volume xvii, February, 1904. 



GEOLOGICAL HISTORY OF THE VERMILION IRON-BEARING DISTRICT OF 



MINNESOTA 



BY J. MORGAN CLEMENTS 



\_ Abstract] 



The Vermilion district has one of the longest geological histories of any region 

 in the world. Since Archean time— represented in this district — there were five 

 great periods of deposition : The Lower Huronian, the Upper Huronian, the Ke- 

 weenawan, the Paleozoic, and the Cretaceous. 



There were four great periods of igneous activity: During Archean time, the 

 great batholithic intrusions at the end of Archean time, the hardly less important 

 batholithic intrusions at the end of Lower Huronian time, and the great Kewee- 

 nawan period of volcanic extrusion and intrusion. There was also possibly con- 

 temporary volcanic activity during Lower Huronian time. 



There were five great periods of orogenic movements, denudation, and meta- 

 morphism: 1, following the Ely greenstone of the Archean; 2, following the 

 Archean series as a whole; 3, following the Lower Huronian; 4, following the 

 Upper Huronian, and 5, following the Keweenawan. 



Also there were three other great periods of denudation, the Cambrian and the 

 Cretaceous periods of baseleveling, and, finally, the period following the Cretaceous, 

 extending to the present time. 



SPHERULITIC TEXTURE IN THE ARCHEAN GREENSTONES OF MINNESOTA 

 BY J. MORGAN CLEMENTS • 



lAbstract] 



The occurrence of spheral ites, some 2 inches in diameter, in great abundance in 

 the basic and intermediate lavas, "greenstones," of Archean age in northeastern 

 Minnesota are described ; also the wide distribution of similar spherulitic green- 

 stones in other districts in the Lake Superior region is emphasized. 



NANTUCKET SHORELINES. I 

 BY F. P. GULLIVER 



[Abstract] 



On account of its exposed position and loose texture the island of Nantucket 

 off'ers a good field for the study of the development of shorelines. There are many 

 important historical changes, many of which have been well recorded on the 



