218 
ME. C. BARRINGTON BROWN AND PROFESSOR J. W. JUDD 
The general conclusions concerning the origin of the rubies of Burma, to which 
we have been led by these studies then are as follows : Pyroxene-gneisses abound, with 
an unstable basic felspar (labradorite or anorthite), which is easily converted by the 
action of minute quantities of hydrochloric acid under pressure into a scapolite ; the 
scapolite in turn breaking up into various hydrated aluminium silicates and calcite. 
In some cases, however, the basic silicate may be converted directly, by carbonic 
or other acids, into a mass of hydrated silicates, quartz, and calcite. Examples 
of such a change are found in the cavities of many amygdaloidal basic rocks. 
Liebrich has recently shown that among the products of decomposition in a basalt of 
Ptiuligheim, near Hanau, is a special form of calcium carbonate occurring in nodular 
concretions with spheroidal and concentric structure, in masses up to and more than 
a foot in diameter. It is noteworthy that this limestone is associated with clav, 
bauxite, and hyalite. # A similar case, occurring in South Africa, has been commu¬ 
nicated to me by Mr. D. Draper, F.G.S. In this connection, it must be remembered 
how frequently calcareous materials make their appearance in masses of altered basic 
rocks—the “ kalk-diabases,” “ kalk-aphanites,” &c., of many authors. The rocks 
known to French geologists as “ hemithrenes,” are probably of similar origin. 
While the limestones are being formed from basic felspars, the aluminium silicates 
taking up water may also be attacked by sulphuric, hydrochloric, boric, or hydro¬ 
fluoric acid acting at moderate temperatures, and the salts of aluminium thus formed 
are easily decomposed ; the aluminium oxide, either hydrated (diaspore, gibbsite, 
bauxite, &c.) being set free, or under certain conditions of temperature and pressure 
the anhydrous oxide itself being formed. The slowdy liberated oxide may assume 
the crystalline form, and thus give rise to corundum. That the crystallization of the 
aluminium oxide took place under great pressure, and probably at moderate tempera¬ 
tures, is indicated by the circumstance that the crystals include not only cavities 
containing supersaturated solutions of chlorides, sulphates, &c., but also, in some 
cases, liquid carbon dioxide, which remains liquid at all ordinary temperatures, 
below r the critical temperature for that gas. 
3. Metamorphoses of the Rubies and Associated Minerals of Burma. 
At the earth’s surface, as is Avell known, corundum, or the crystallized oxide of 
aluminium, is one of the most unalterable of substances. Fragments found in river 
gravels and sands, though perfectly water-worn, show no trace of chemical altera¬ 
tion in their surfaces. On the other hand, there can be no doubt that conditions 
must exist in the earth’s crust, under wdiich chemical change of this mineral does 
take place ; this is abundantly proved by the frequency with which undoubted 
* ‘Neues Jalirb.,’ 1893, vol. 2, p. 75. 
