218 THE MARQUETTE IKON-BEARING DISTRICT. 



0.2 per cent apatite. They jxiint clearly to the fact that these rocks are 

 composed of granitic material that has been silicified. 



INTRUSIVES IN THE SOUTHERN COMPLEX. 



In the Southern Comple.x, as in the Northern Coni})lex, the schists and 

 granites are cut by well-characterized dikes and veins of eruptive material. 

 The characters of the dikes in both areas are much alike. They comprise 

 diabasic, epidioritic, and aplitic kinds. The liasic dikes were evidently 

 formed at different times, for some of them are schistose and are clearly 

 altered diabases, while others are beautifully fresh and entirely massive. 

 The latter must be much vounger than the former. They were perhaps 

 intruded during Keweenawan time, for they are identical in composition 

 and general character with the smaller dikes cutting Upper Marquette 

 sediments, while at the same time none of them have been found pene- 

 trating the Cambrian. Among the materials of the fresher dikes may be 

 mentioned ophitic diabases, olivine diabases, basalts, luster-mottled gabbro- 

 like diabases, and uralitic diabases. 



The older and usually larger dikes are epidioritic and uralitic schistose 

 diabases, exactly like similar rocks in the Northern Complex, and practi- 

 cally identical with the material of the large, boss-like dike masses in the 

 Algonkian. (See Chapter V.) 



SUMMARY. 



The rocks of that portion of the Southern Complex discussed in this 

 volume are micaceous and hornblendic schists, greenstone-schists, gneissoid 

 granites, certain schists that have V)een called "Palmer gneisses," and acid 

 and basic dike masses. The greenstone-schists, the granites, and the dike 

 materials are similar in their essential features to the corresponding- rocks of 

 the Northern Complex. All are igneous in origin. The greenstone-schists 

 are squeezed basic lavas or tuffs. They are older than the granite. The 

 dike masses are in all respects like those that penetrate the northern area. 



The Southern Complex differs from the northern area in the smaller 

 quantity of greenstone-schists in the former, and the presence in it of the 

 micaceous and hornblendic schists and the Palmer gneisses. The latter 



