I 



152 THE VERMILION IRON-BEARING DISTRICT. 



of the metadolerites (diabase) and metabasalts. The rocks possessing tliese 

 textures occur in very large quantity throughout the district. These 

 textures are common in the recent basalts. The mineralogic composition 

 of the rocks is also the same as would be produced in recent basalts by 

 alteration. Hence, in the absence of chemical analyses, the writer feels 

 warranted in asserting that the greater portion of these greenstones was 

 derived from the alteration of originally basaltic rocks. 



Spherulitic texture is fairly common in these altered basalts, and on 

 account of its somewhat greater interest deserves a little more detailed con- 

 sideration than has been given to the others. The sphei'ulite occasionally 

 has at its center a very small crystal of plagioclase surrounded by fine 

 sheaves of feldspar, and these spherulites are very similar to those described 

 some years ago from Michigan." The feldspars are brownish when seen 

 under low power and grayish when examined by high power, as the result 

 of the innumerable minute crystals of epidote, a few hornblende individuals, 

 and reddish-brown to black spots of ferruginous material. Other spherulites 

 consist largely of feldspar, but between the feldspars occur needles of 

 actinolite, which seem to have been derived from some original ferromag- 

 nesian mineral which, with the feldspars, formed the spherulite. There were 

 found in one case in a much altered greenstone, instead of the usual feldspar 

 spherulites, radial masses of rich green chlorite with silky luster. The 

 microscope showed a few crystals of magnetite and some epidote in these 

 spherulites in addition to the chlorite. 



With the above kinds of rocks, which are unquestionably of basaltic 

 character, there are rocks tliat possess an intersertal, pilotaxitic, and liyalo- 

 pilitic texture, in some of which porphyritic feldspars, occurring in isolated 

 individuals or in groups, are very common. In these rocks there seems to 

 be a large proportion of brown hornblende, sometimes occurring as pheno- 

 crysts. The general appearance of the rocks is like that of the andesites. 

 It appears that, associated with the basalts and playing a subordinate r6le 

 in this district, there are rocks of intermediate composition which were 

 originally andesites — both hornblende- and pyroxene-andesites — and that 

 we are justified in stating that meta- andesites form a part of the Ely green- 

 stone. 



"The Crystal Falls iron-bearing district of Michigan, by J. Morgan Clements: Mon. IT. S. Geol. 

 Survey Vol. XXXVI, 1899, p. 111. 



