476 THE CEYSTAL FALLS IRON-BEAEING DISTRICT. 



On the old road leading- to the dam the conglomerates and arkoses are 

 intruded by an altered diabase in a most complex way. To the north of 

 the road is the great mass of the greenstone, within which are considerable 

 areas of the conglomerate. Within the belt of conglomerate, on the other 

 hand, are several bands of the eruptive rock which roughly follow the bed- 

 ding of the sedimentary one, but which cut across it in a minor way. 



At the contact of the main mass of greenstone and the conglomerate 

 are numerous interlaminations of the two rocks, the greenstone having 

 intruded the conglomerate along its bedding planes. At one place a dozen 

 alternations of the two were noted within a foot. Moreover, for some 

 distance from the greenstone the conglomerate appears to be impregnated 

 with material from the intrusive, so that it has taken on a greenish tinge. 

 This impregnation in one instance has gone on so far as to produce what is 

 apparently a greenstone matrix containing separate pebbles from the con- 

 glomerate, the groundmass of the conglomerate having apparently been 

 absorbed. The greenstone adjacent to the conglomerate is traversed by 

 narrow pegmatite veins in various directions, some of the lai-gest being not 

 more than 2 inches in width. There is no evidence of a granitic intrusion, 

 the pegmatites appearing clearly to be the result of an interaction between 

 the basic igneous rock and the more acid fragmental one. At one place 

 along the contact there is a belt of very coarse hornblendic material that is 

 cut through and tlirough by the pegmatite veins. 



East and west of the dam for some distance are other ledges of con- 

 glomerate. They, however, as a rule, present no features difiPerent from 

 those exhibited by the great ledge described above. In all, especially in 

 those occurring in sees. 9 and 10, T. 42 N., R. 28 W., the interbanding of 

 conglomeratic and nonconglomeratic layers is beautifully shown. 



Near the north quarter post of sec. 11, T. 42 N., R. 28 W., the arkoses 

 have a purple rather than a pink tinge. On cross fractures they are seen to 

 be spangled with glistening black needles and plates of hornblende, which 

 lie with their long axes in all azimuths. The little crystals appear to be 

 more abundant in some layers than in others. 



The best exposures of quartzite are found near the north quarter post 

 of sec. 11, T. 42 N., R. 28 W., and at 1,300 paces W., 150 N., of the south- 

 east corner of sec. 7, T. 42 N., R. 29 W. The rocks are black. They occur 

 in beds varying in thickness from a few inches to several feet. 



