288 THE VERMILION IRON-BEAEING DISTRICT. 



On the hill just south of Mud Creek Bay the conglomerate is exposed 

 at a number of places. As a result of the close folding it appears in very 

 complex relationship with different rocks, namely, the Ely ellipsoidal 

 greenstone and the various granitic rocks of Vermilion Lake. After a 

 careful study of the exceedingly intricate contacts between the porphyries 

 and the conglomerates, which at first led to the belief that the porphyries 

 were intrusive in the conglomerates, it was found that this relationship 

 was due to the close infolding of the rocks, giving zigzag and most irregular 

 contacts. This relationship, as has already been stated in previous pages, 

 was proved by the identification of the porphyry pebbles in the conglom- 

 erate with the adjacent porphyries. The detailed map. Sheet XXV of the 

 atlas, shows the areal distribution of these rocks on this point and will give 

 some idea of the intricacy of the distribution. 



Reference has already been made to the rocks occurring on Ely Island. 

 A good place at Avhich to study the close relationship of these rocks is 

 the east end. Here there is a most intricately folded complex of moderately 

 fine-grained granite-porphyry, conglomerate, and gray wacke. The distribu- 

 tion of these is shown on the detailed map forming fig. 18. The gray wacke 

 and porphyry when looked at casually resemble each other very strongly, 

 but when examined closely they can readily be distinguished. The por- 

 phyry is studded with small phenocrysts of quartz and, as a result of 

 weathering, develops an exceedingly rough surface in detail, something like a 

 nutmeg grater. The graywacke contains grains of quartz which in many 

 cases, and probably in most cases, are phenocrysts derived from the 

 porphyry and in some instances are very slightly worn. This graywacke 

 weathers in genei'al with a smooth surface, and this difference in the 

 weathering alone will usually enable one to distinguish the two kinds of 

 rocks. Where the graywacke is in very massive exposures, and especially 

 where the graywacke and porphyry have both been sheared, it is at times 

 extremely difficult to separate them. As the result of the shearing and 

 subsequent weathering both the porphyry and the graywacke are likely to 

 develop a series of small parallel ridges or corrugations on the surface. 

 This corrugated way of weathering was not so noticeable, however, on the 

 porphyry as on the graywacke. At this place the infolding of the porphyry 

 and the sediments is exceedingly complex. We find fingers of the one 

 interlocked with fingers of the other, so that the contact forms a zigzag 



