XL] GRANITES AND GRANITIC VEIN-STONES. 213 



rounded angles are much less fusible than those which, in 

 contact with them, preserve their crystalline forms intact. 

 (Geology of the First District of New York, pages 57, 58.) 

 These facts are well shown in the apatite-veins of Elmsley and 

 Burgess, Ontario, where the crystals of apatite rarely present 

 sharp or well-defined forms, but (whether lining drusy cavities 

 or imbedded in the calcite or other minerals of the vein-stone) 

 are most frequently rounded or sub -cylindrical masses, while 

 the pyroxene and sphene, which often accompany them, pre- 

 serve their distinctness of form. This rounding of the angles 

 of certain crystals appears to me nothing more than a result of 

 the solvent action of the heated watery solutions from which 

 the minerals of these veins were deposited ; the crystals pre- 

 viously formed being partially redissolved by some change in 

 the temperature or the chemical constitution of the solution. 

 Heated solutions of alkaline silicate, as shown by Daubree, 

 are without action on feldspar, as might be expected from the 

 fact observed by him of the production of crystals of feldspar, 

 as well as of pyroxene, in the midst of such solutions. These 

 liquids would, however, doubtless attack and dissolve apatite, 

 which is in like manner decomposed by solutions of alkaline 

 carbonate, and these latter at elevated temperatures dissolve 

 crystallized quartz. That this solvent process has been re- 

 peated during the filling of the veins is seen by a specimen 

 in my possession, which shows crystals of calcite previously 

 rounded and enclosed in a large crystal of quartz, the angles 

 of which are also nearly obliterated. From the alternations in 

 the deposited mineral matters in many vein-stones, as well as 

 from what we know of the changing composition of mineral 

 springs, it is evident that the waters circulating in the fissures 

 now occupied by veins must have been subject to periodical 

 variations in composition. 



43. In the Geology of Canada (page 729) I have noticed 

 an example of rounded quartz crystals in the veins at the 

 Harvey Hill copper-mine in Leeds, Quebec. Large terminated 

 prisms of limpid colorless quartz are there found imbedded 

 in compact erubescite, their angles being much rounded, while 



