LITHOLOGY. 23I 



localities as the quartz dioritcs. Lancaster and Littleton are favorable 

 places for its observation. Specimens from these places show, in thin 

 sections, much hornblende, and variable amounts of quartz, and plagio- 

 clase which is at times quite prominent, but is subordinate to the quartz 

 in amount. Decomposing titanic iron, epidote, and sphcne are present, 

 and hence our amphibolitcs differ from the diorites only in the elimina- 

 tion of the feldspar. A specimen from Northumberland is entirely com- 

 posed of hornblende, with the exception of some microscopic biotite and 

 pyrites. The hornblende of all these rocks is of the green fibrous variety. 

 Its crystals lie at all angles and in all planes, and in this it differs from 

 the schists next to be described. 



Hornblende Schist. This is a very prominent rock in the greenstone 

 series. It is usually very dark in color, and is composed of deep green 

 hornblende, the needles or crystals of which mostly lie in the plane of 

 lamination of the rock, and considerable quartz is interspersed with it. 

 This quartz is often very conspicuous in thin sections when it is scarcely 

 recognizable in the mass. The hornblende, which usually is in long, 

 irregular, and fibrous crystals without definite form, does sometimes, in 

 the more quartzose varieties, assume the outlines natural to its crystals. 

 Fig. 2 on PI. 7 is drawn from a section of this schist from Cornish. The 

 hornblende is trichroic (see p. 6i), and its crystals, though possessing in 

 some cases well defined prismatic planes, are always entirely lacking in 

 terminal planes. This schist contains, in addition, microscopic magnetite, 

 garnet, biotite, plagioclase, and epidote. The last four ingredients are not 

 represented in the figure. Other specimens, in addition, contain ortho- 

 clase, titanic iron, and pyrite. A variety from Stewartstown is remarkable 

 for the large amount of epidote that it contains, which, though only micro- 

 scopically recognizable, impresses its color on the rock. A variety from 

 Hanover is celebrated for its garnet crystals, which are very perfect little 

 dodecahedrons of a deep red color. Sprinkled so abundantly through the 

 almost black hornblende, they make a very pretty rock. Though appar- 

 ently so clear and pure, these garnets in reality are quite largely com- 

 posed of quartz, as is shown by Fig. 5 on PI, 4, which is drawn from a 

 section that passes through one of them. This is a fair representation 

 of the garnets as they ordinarily appear in sections of the greenstones. 

 They are like crystals that form in a plastic mud, rather than in a more 



