138 THE MARQUETTE IRON BEAKING DISTRICT. 



The Cascade fonnatiou sliows best its relations to tlie younger forma- 

 tions near tlie Volunteer mine, on the Cascade range. 



Here one finds an old honiblendic scliist tliat has been invaded by eruptive 

 granite and other volcanic rocks. * * * It is not impossible that the hornblendic 

 schist may be au altered eruptive or volcanic rock, instead of being a sedimentary 

 one, although the evidence thus far obtained points to the latter origin. 



Near the mine the Republic formation, with a basal conglomerate, may 

 be seen rej)osiug unconformably upon the Cascade rocks, and imconform- 

 ably above these may be seen the Hoi yoke rocks. 



The rocks comjirising the Cascade formation have already been men- 

 tioned. Some of them are detrital accumulations derived either from an 

 older formation or from some volcanic source. It may be that the Cascade 

 series should be divided into two parts, since it appears that in a few areas 

 some of the gneisses are eruptive in origin instead of fragmental, as is 

 the case with most of the Cascade gneisses, which are younger than the 

 eruptive gneisses and contain fragments of tliem. All these gneisses are 

 cut bv granites and by liasic dikes. 



The composition of the Kepul^lic fornuvtion has already l)een outlined. 

 In it are most of the jaspilites of the district. These, it is stated, may still be 

 regarded as eruptive at Ishpemiug and Negaunee, though elsewhere they 

 seem to be sedimentary. The phenomena formerly supjiosed to prove the 

 eniptive origin of the jaspilites and ores are shown to be explained by 

 the eruptive nature of the green schists with which they are in contact. 



The sedimentarv t)rigin of the jaspilites is plainly shown in the Cascade 

 range, south of Palmer, where these rocks are interlaminated with quartz- 

 ites, often in thin beds. Some of the beds contain fragments of banded 

 jaspilite, which would indicate that there is an occurrence of this rock some- 

 where beneath the Republic fomiatiou. Moreover, most of the jaspilites 

 interlaminated with the quartzites "appear to be composed of a tine 

 jas])ilite mud derived from the jaspilitic debris." 



The belief in the existence of jaspilite in the Cascade formation rests 

 upon the evidence just given; but the author thinks it possible that the 

 jaspilite fragments in the conglomerates may have I'ome from veins in 

 the older rocks, although these are rarely observed. 



