110 THE PENOKEE IRON-BEARING SERIES. 



grains aru iiiiuutely angular. A general oval I'urni is also very marked with 

 some of the feldspars (PI. xiv, Fig. H). The larger feldsjiars in the coarser 

 phases of the rock are about 1""" in greatest length. They are nearly all 

 striated and have the appearance of this mineral in ordinary basic eruptives. 

 Included in the feldspars are blades of hornblende and grains of quartz, 

 the latter in some cases averaging not more than ^oUini in diameter. 

 Manifestly either the feldspar has crystallized sul)sequently to the quartz 

 and hornblende, or, and this is })erhaps more probable, the decom[)osition 

 of the felds})ar has formed the hornblende and quartz. The appearance of 

 the hornblende individuals both within and without the feldspars is such 

 as to suggest that they are now in the process of growth (Plate xiv, Fig. 

 4). In general the feldspar is badly altered, so that it not only includes 

 hornblende and quartz, but a gray decomposition product taken to be 

 kaolin. When the alteration of a large feldspar has proceeded far, the 

 area niay consist of many detached particles of feldspar, included in which 

 are large hornblendes and numerous quartzes. Unless examined closely 

 this peculiar relation would not be noticed and the area would be concluded 

 to be an intricately interlocking one in which the particles of feldspar are 

 independent, as they are recognized only as a skeleton of a single feldspar 

 when closely examined in polarized light. The hornblende is of the pale 

 green variety ; it has normal plejochroism and extinction. The individuals 

 do not have well defined outlines, but fray oiit in every direction in ragged 

 stringers (PI. xiv. Fig. 4). This is esjjecially noticeable in sections cut 

 parallel to the vertical axes, but is also distinctly seen in transverse sec- 

 tions. If this mineral was the first to crystallize, as must be the case if all 

 those individuals now present are original crystallizations, the exceedingly 

 ragged forms are inexplicable. If, U})on the other hand, the .hornblende is 

 a product which has formed subsequently to the feldspar, these are pre- 

 cisely the forms which would be expected. It thus seems probable that 

 these rocks are much altered ones which originally contained much more 

 feldspar than at present ; perhaps those containing hardly any feldspar being 

 as feldspathic as those of the gneiss which contains a large amount of this 

 mineral. In some of the sections biotite is as alnmdant as the hornblende. 

 It is intimately associated with that mineral and bears the same relation to 



