748 PRE-CAMBRIAN NORTH AMERICAN LITERA TURE 



unusual relations are explained as due to faulting approximately par- 

 allel to the fold which occurred during the folding of the series. 



Van Hise' describes the rocks of the Marquette district as con- 

 stituting a great synclinorium. The axial planes of the minor folds 

 on the sides dip toward the center of the synclinorium, thus resembling 

 the fan structure of the Alps ; but there is the great difference that the 

 major fold is a synclinorium rather than an anticlinorium. This kind 

 of fold may be called the Marquette type. 



Clements'" describes the volcanic rocks of the Michigamme district of 

 Michigan. The succession in the district from the base up is (i) granite 

 and gneiss, cut by basic dikes ; (2) quartzose limestone formation, with 

 an estimated thickness of 1500 to 2000 feet; (3) a great series of vol- 

 canics, with an average thickness of about 3000 feet; (4) a set of sedi- 

 mentaries consisting of quartzites, slates, and iron formation material. 

 The volcanics include apobasalts, apo-andesites, and aporhyolites, each 

 occurring both as lavas and as tuffs. The lavas are frequently amygda- 

 loidial. 



Smyth (H. L.),^ compares the Lower Menominee and Lower Mar- 

 quette series in Michigan. The Lower Menominee series consists in 

 ascending order of 



1. A basal quartzite, rarely conglomeratic, having a thickness of 

 700 to 1000 feet. 



2. A crystalline limestone, averaging 700 to 1000 feet in thickness. 



3. Red, black, and green slates, not known to exceed 200 or 300 

 feet in thickness, and containing the iron formation that gives the 

 rich ores of Iron Mountain and Norway. Toward the north the hori- 

 zon of the slates is in part occupied by later eruptives, that rapidly 

 increase in thickness and attain a maximum of nearly 2000 feet. 



4. The Michigamme Mountain jasper. The least modified phase 

 seems to be in part at least a sediment. The most highly altered kind 

 is like the banded, specular jasper of Republic. 



' Character of Folds in the Marquette Iron District, by C. H. Van Hise. Proc. 

 Am. Assoc, for Adv. of Sci., for 42d Meeting, 1894, pp. 171. (Abstract.) 



*The Volcanics of the Michigamme District of Michigan (preliminary), by J. 

 Morgan Clements. Journal of Geology, Vol. Ill, 1895, pp. 802-822. 



s Relations of the Lower Menominee and Lower Marquette Series of Michigan 

 (preliminary), by H. L. SMYTH. Am. Jour. Sci. (Ill), Vol. XLVII, 1894, pp. 216-223. 



