THE CRYSTALLINE ROCKS NEA.R ST. JOHN, N. B. '61 



"through later folding and erosion, these altered rocks 

 were once more hronght to the surface, as we see them 

 now. 



Characierisfic Structures of Volr<niic JRocks. — In 

 Tuodern glassy lavas we usually see imperfect forms of 

 crystallization, one common type of which is composed 

 -of a quantity of minute needles of crystalline quartz and 

 feldspar, radiating out from a centre and forming a little 

 hall, called a spherulite. These spherulites are still pre- 

 served in some of our ancient lavas, and give one proof 

 of their original character. Again, in modern lavas, or 

 slags, we often see a series of wav}^ parallel lines, produced 

 hy the ilowing of one part of the viscous fluid over 

 another. These "flow-lines'' are often to he seen in 

 some of the old Xew Brunswick lavas. In the upper 

 2:>art of a lava flow, the contained water, relieved from 

 pressure, hursts into steam and fills the lava with little 

 cavities, or vesicles. So, too, in parts of these old volcanic 

 flows we find vesicles abundant ; but they have subse- 

 quently been filled in with quartz and calcite by the 

 mineral-bearing solutions which contrive to seep into the 

 rock during its metamorphism. Such are some of the 

 proofs of the volcanic origin of the?^e rocks. 



The breccias are seen to be made up of angular frag- 

 ments of rock of all sizes and lying " every which way."' 

 The whole mass at the same time is flinty, and breaks in 

 the same wa}- as the felsites. In thin sections we can see 

 that it is made up entirely of pieces of lava, large and 

 small, which often show some of the characteristic 

 structures of which I have spoken. 



Some of these rocks have been so much metamor- 

 phosed that they have taken on a schistose structure, and 

 almost nothing is left of their original character, which 



