THE NORTHERN COxMPLEX. 151 



acid dikes and bosses and by granite and (juartz veins. Near Lake Superior 

 tlie two series are separated by a small area without outcrops, except occa- 

 sional ledges of Potsdam sandstone. Whatever rocks may underlie this 

 area, they are buried deep beneath Pleistocene sands and gravels. Else- 

 where the exposures of the two sei'ies are close together, and at many 

 places actual contacts may be seen. 



The rocks comprising the Northern Complex are gneissoid granites, 

 syenites, greenstone -tuffs, greenstone - conglomerates, greenstone -schists, 

 peridotites, aplites, vein granites, diabases, diorites, and epidiorites. The 

 first five are at many places highly foliated, while the last six are massive, 

 or but slightly schistose. The former occupy the greater portion of the 

 belt, so far as it is within the limit of the map (Atlas Sheet IV). They 

 are older than the latter, which cut them in the form of dikes and bosses. 



The foliated rocks occupy areas whose boundaries are not so well 

 defined as is the case with the Marquette fragmentals, since the schists 

 and the granitoid gneisses and syenites gradually pass into one another, 

 through the intrusion of the liasic rocks by dikes and veins of the acid 

 ones. Nevertheless, an attempt has been made to map these areas. In 

 their interiors the different phases of schists, granites, and syenites are well 

 characterized, but on their ])erip]ieries there is always a complex mixture 

 of the various schists with one another or with the granitic rocks. The 

 respective colors on the map are believed to cover the areas within which 

 the corresponding rocks predominate largely over other rocks. Tlie bound- 

 ary lines separating the different areas are drawn at about the places where 

 the different varieties are found in approximately equal quantities. 



The greenstone-schists include two classes. The rocks of the first class 

 are nonconglomeratic green schists. These are called the Mona schists, 

 because good exposures are found on hills of this name southwest of 

 Marquette. Those of the second class contain pebble-like bodies, and 

 these are discussed separately. Their best development is on the Kitchi 

 Hills, in the neighborliood of Deer Lake, northwest of Ishpeming, and 

 hence they are called the Kitchi schists. They have frequently been 

 referred to in the literature on the district as the Deer Lake conglomerates 

 or agfj-lomerates. 



