!* " 372 [Proc. B.N.F.C., 



next thing after the chemical elements are the crystals]of which 

 the primitive rocks are composed ; for crystals are built of 

 chemical elements ; and rocks are built of crystals ; and 

 mountains, which are the primitive land, are built of rocks. It 

 is an ascending scale of buildings. 



The Crystals of which the Rocks are built are very numerous 

 and we must be content with a very small sample. Let us take 

 what comes readily to our hand. We cannot go far in Co. 

 Down till we are in the midst of Granite mountains ; nor can 

 we take a long ramble in Co. Antrim till we are deep among 

 the Basalt Dykes and Masses, with which very interesting 

 rocks Antrim is specially rich. Granite and Basalt will serve 

 us here. How, then, is granite built ? As to the place and 

 manner of the build of granite it seems to be deep down in the 

 earth, and away trom the quick cooling caused by exposure 

 near the surface. It is called a Plutonic rock as distinguished 

 from a Volcanic one; such as we have in the Basalts, called 

 Volcanic because of being forced up to near the surface of the 

 earth and more or less exposed to the rapid chilling of surface 

 agencies. For this reason the chemical elements which build 

 up Granites have plenty of time to crystallize ; and so we find 

 that Granite is composed entirely of crystals, not embedded in a 

 cement or paste, like the crystals of Basalts, but jammed 

 together and interlocked one with another ; well formed, save 

 as they confine each other by pressing contiguity. 



And now as to the materials of granite. Granites are built 

 chiefly of Quartz, Felspar, and Mica crystals ; many varieties 

 of these plutonic rocks have various additional elements, but 

 these three are the chief. And now considering only those 

 three let me try to give you some idea of the wonderful 

 complexity and harmony of their build. 



In brief, at this point, the way to read the musical notes of 

 any crystal may be illustrated thus : — take Quartz, it is composed 

 of Silicon and Oxygen. Silicon is the fourth element in the 

 second octave of Mendelejeff's table of the elements ; and 

 Oxygen is the sixth in the first octave. Now the fourth in the 



