XL] GRANITES AND GEANITIC VEIN-STONES. 211 



39. Evidences of the concretionary origin of these granitic 

 vein-stones of the Laurentian rocks appear in their banded 

 structure, their drusy cavities, the peculiar incrustations and 

 modes of enclosure often observed in the crystals, and finally 

 in the rounded forms of certain crystals, which show a process 

 of partial solution succeeding that of deposition. A banded 

 arrangement of the materials parallel to the sides of the vein is 

 often well marked. Thus, while the walls may be coated with 

 crystalline hornblende, or with phlogopite, the body of the vein 

 will be filled with apatite, in the midst of which may be found 

 a mass of loganite, or of crystalline orthoclase mixed with quartz, 

 filling the centre of the vein, as already noticed in 36. In 

 other instances portions of the vein will be occupied by crystals 

 of apatite, pyroxene, or phlogopite imbedded in calcareous spar, 

 which in some other part of the breadth of the vein, or in its 

 prolongation, will so far predominate as to give to the mass the 

 aspect of a coarsely crystalline lamellar limestone. Prisms of 

 apatite are often observed extending from either side toward 

 the centre of the vein, which in some cases may be filled with 

 calcite or another mineral, and in others is a vacant space lined 

 with crystals. Drusy cavities of this kind, a foot in breadth 

 and several feet in length and depth, are sometimes met with 

 in these veins in Ontario. 



40. Further evidence of concretionary origin is seen in the 

 manner in which the various minerals incrust each other. Thus 

 small prisms of apatite are enclosed in large crystals of phlo- 

 gopite, in pyroxene, in quartz, and even in massive apatite ; 

 crystals or rounded crystalline masses of calcite are imbedded 

 in apatite and in quartz, and well-defined crystals of hornblende 

 (pargasite) in pyroxene. In another example before me, small 

 crystals of hornblende are implanted on a large crystal of 

 pyroxene, and both, in their turn, are incrusted by small crys- 

 tals of epidote. Crystalline graphite in like manner is enclosed 

 alike in orthoclase, quartz, calcite, phlogopite, and pyroxene. 



41. Another noticeable evidence of the concretionary origin 

 of these veins is the phenomenon already referred to in 25, 

 where the external skeleton or framework of a crystal is com- 



