378 THE PENOKEE IRON-BEARII^G SERIES. 



presence nt' tVagmeuts of a basic eraptive, althoiigli a few exposures of a 

 schistose noncon<i'lonieratic material are found. These fragments, as has 

 been seen, vai'\- from tliose which are well rounded to those which have 

 the extreme of ;ingidarity. Basic eruptive fragments of this sort ma}- 

 have been derived from various possible sources, those which are well 

 rounded having been probiiblv, ;dthough not certainly, subjected to water 

 action, but this does not necessarily tell their source. It has been seen 

 that south of tlu^ iron-bearing lielt of the formation is a layer of amygda- 

 loidal por[)h>'rite; also, very closely associated with the conglomerates 

 themselves in the northern portion of the area are other large exjjosures of 

 a similar i-ock. These massive rocks are remarkably like many of the 

 pebbles contained in tlie greenstone-conglomerates. It is, then, possible 

 that the fra2:nients of the orreenstone-couglomerates have been derived liv 

 the degradation of older or contemporaneous eruptive outflows, or it is 

 possible that they are the direct ejecta from a \-olcanic vent, or (and this is 

 most likely the case) the pebbles have in })art come from both of these 

 sources. 



The oreenstone-conolomerates and breccias, which have a matrix 

 essentially like ;in altered greenstone and most irregular fragments of 

 basic eruptives with dithculty separated from the matrix, have a remark- 

 able likeness to the schistose fine grained })or|)h}-rites with which thev are 

 closely associated in the hehi This material certainly can not have resulted 

 from tlic l)reakiiig down ot' a soliditied I'ock b\- water action. The frag- 

 ments are preeisel}' like in their shape and character to the ejecta of a 

 volcanic vent, llow these fragments and the matrix in ^vhich they are 

 containeil became mingled it is impossil)le to sav witli certaint}'. The 

 brecciation may be merely that of an onflowing l)ed of lava which i-on- 

 tinues its forward movement after it has i-eached so viscous a condition 

 that it becomes fractured in every direction by its motion, caused by a 

 force in the rear, or this mixture may be the ejecta from a ((ine falling- upcm 

 a lava stream Ho wing down Its side. The first explanation is regarded 

 as the more i)rob;d)l('. Whichever h\pothesis is true, tliat this material 

 is essentially tlw same in com])osition as the sinTounding surface lava 

 flows is certain, for take away the fragments and it would be impos- 



