T. Sterry Hunt on Granitic Rocks. 121 
idocrase half an inch in diameter, from a vein in Grenville, 
Ontario, composed chiefly of orthoclase and pyroxene, is seen 
when broken across to consist of a thin shell of idocrase filled 
encloses a small crystal of zircon. In like manner large erysta 
of zircon from similar veins in St. Lawrence County, New York, 
pe sometimes shells filled with calcite. 
crystalline form is nearly or ~~ effaced, the surface being at 
the same time smooth and s 1 
serve their crystalline forms intact (Geology of the First Lns- 
trict 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 veinstone, are most frequently rounded or 
sub-cylindrical masses, while the pyroxene and sphene, which 
often accompany them, preserve 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 previously formed being partially redisso ved by 
some change in the temperature or the chemical constitution of 
the solution. Heated solutions of alkaline silicate, as shown 
by Daubrée, are without action on feldspar, as might be 
expected from the fact observed by him of the production of 
ee 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 decom y solu- 
tions of alkaline carbonate, and these latter at elevated tempera- 
