230 MINERALOGY AND LITIIOLOGY. 



fine ill texture, but the development of larger feldspar crystals makes it 

 porphyritic. In thin sections, the hornblende is entirely of a fibrous char- 

 acter; the feldspar is very impure, both as a result of decomposition and 

 original inclusion of impurities. The quartz is tucked away in little cor- 

 ners. In this rock the titanic iron assumes the most fantastic forms, but 

 it is mostly altered into the gray product which is characteristic of all 

 these diorites. This subject, however, needs no further illustration, 

 Epidote, chlorite, and si)hene are present in small amount. Tyrite is 

 abundant. Apatite, which is so prominent in the basic eruptive rocks, 

 is here but rarely seen. 



At Lancaster these rocks are abundant. Some are very dark in color 

 when hornblende predominates ; some are yellowish-green when feldspar, 

 filled with epidote, predominates, and all those variations in composition 

 are met with which might be expected as a result of the mctamorphism 

 of sedimentary beds. 



AMPHIBOLITE. 



Amphibolite is a granular massive or schistose rock, which is com- 

 posed of amphibole with more or less quartz. Accessories, as usual, 

 are present. We have the following varieties to describe : 



Amphibolite (massive hornblende rock). 

 Hornblende Schist. 

 Actinolite Schist. 



These rocks are very prominent among the greenstones. Their horn- 

 blende possesses the same crystalline character as that of the diorites 

 last described. Their relation to the diorites is shown by the frequent 

 presence of triclinic feldspar. Indeed, some of the rocks rich in plagio- 

 clase might be called quartz diorite if one chose to draw the line at a 

 different point. This is not an unusual circumstance, for such grada- 

 tions have been elsewhere observed. For example : among the so-called 

 ophites of the Pyrenees there are amphibolites, which, by the gradual 

 introduction of plagioclase, are stated to pass by insensible stages into 

 typical diorites; — and so we have a familiar association of rocks here, 



Amphibolite. This rock is a very nearly massive aggregate of horn- 

 blende crystals, or of hornblende and quartz. It occurs in the same 



