THE HOIINBLEXDIC SCHISTS. 207 



quantity, when the rocks are inucli like the hist type of" tlic p-eenstone- 

 schists mentioned above. Sometimes it is present in very lai-ye (piantity, 

 when they reseinble true hornblende-schists. Usualh- quartz and fresh 

 plagioclase are present in about equal amounts, and in tliis case the rocks 

 are intermediate in character between the g-reenstonc-schists and the true 

 hornblende-schists. 



In the hand specimen the rocks of this class have a dark-gray or 

 black, rather than a green, tinge. Many of them are lustrous, black, highly 

 foliated schists that are sometimes banded with very fine parallel lines of a 

 white and a dark-green color, but Avhich more frequently are of a uniform 

 dark color; others are medium-grained, dark-gray, dioritii'-looking rocks, 

 in which a foliation is clearly apparent, but is not marked in its perfection; 

 while a few are fine-grained, black schists of a dense, uniform texture. In 

 thin section difi^erences in conq)osition and texture may be detected, corre- 

 sponding with diff'erences in the macroscopic appearances of the rocks. 



The less lustrous of the schists resemble most closely the greenstone- 

 schists. Quartz and clouded plagioclase are present in very nmch elongated 

 grains, between which are flakes and masses of green hornblende and 

 chloritized biotite in small quantity. Large plates of epidote and grains of 

 titaniferous magnetite, surrounded by leucoxene, are scattered tln-ough the 

 aggregate. The bands that are sometimes so plainly seen in the hand 

 specimen are not clearly defined under the microscope. They can be rec- 

 ognized, but they possess no distinctive features. The darker bands contain 

 more amphibole than do the lighter ones. Otherwise the two are similar, 

 both in composition and in structure. 



The lustrous schists are very fresh looking. Now and then a turbid 

 grain of feldspar is seen in their sections, but this happens rarely. As they 

 are now constituted the rocks difl^er from the "diorites" described under the 

 greenstone-schists in containing a little c^uartz. Elongated fresh plagio- 

 clase, mxich of which is untwinned, prisms of conq^act green hornblende, 

 and grains of quartz are the only components present in any quantity. A 

 few grains of epidote and some of magnetite, and occasionally a flake ot 

 brown biotite, are also met with, but not in noticeable amounts. In one or 

 two instances the feldspar is in such small quantity that the rocks are 

 essentially amphibole and quartz aggregates. 



