56 The Aiiieric(ni Geolor/isL July, 1895 
The crystiilli/.iitioii ui' tliis miin-ral from ;i fused mass is certainly not 
impossible. Tlie l,esls of I\l. Hautefenille sufticiently show that, but it is 
at least very difficult. The i)ro(luction of albite, therefore, is scarcely 
probable in theseiconditions, even when the generating magma possesses, 
either originally or after various liquations or crystallizations, a com- 
position whicli is ni^arer that of albite than of anorthite. 
But the objection just presented, although very strong, does not con- 
stitute, however, an argument which cannot be answered. It may be 
said, indeed, that the formation of a crystalline molecule of anortiiile 
may exert a decisive influence ui)oii the formation of a molecule of al- 
bite, and that that which is not possible in the absence of a basic ele- 
ment takes place easily in its presence, especially at the moment when 
its atoms are th(; seat of intense movement. In chemistry such cases 
are common. A body which refuses to crystaJli/.e when it is alone, for 
want of a solvent, often crystallizes readily under the action of a neigh- 
bor of similar constitution, or even, sometimes, of unlike constitution. 
In this case anorthite would i)lay a role of this kind, and would be the 
element which would determine the crystallization of albite. 
The objection, therefore, leads to controversy. Let it be set aside, 
and let the discussion be confined to the decisive fact which appears to 
demand an interi)retation of the law of Tschermak different from that 
which is generally adopted. 
This fact is the frequent observation of certain of the types of feld- 
spar which are intermediate between albite and anorthite, and the rar- 
ity of certain others. The studies that I have set forth in previous 
portions of this work appear to me to leave not the least doubt on this 
fact, however inexplicable under tlie hypothesis of an association or 
physical mixture of albite and anorthite. 
The serial discontinuity, indicated in the group of the lime-soda 
feldspars, is still more evident in the potash-soda feldsi)ars, without 
speaking of certain anomalies peculiar to this last group. In order to 
account for this fac^ it appears to me necessary to admit that between 
albite and anorthite there exists a certain number of intermediate feld- 
spars with a definite comi:)osition, forming by themselves a natural fam 
ily, a series that may be compared to similar series so well established 
in organic chemistry. In the series to which I allude, the extreme 
terms being known, the properties of the intermediate compounds are 
exactly determined. It may be supposed that the same can occur in 
the inorganic world. Such a hyi)othesis, at least, offers nothing contra- 
ry to ordinary scientific principles. 
If this is admitted it leads to the same practical conclusions as the 
theory of Tschermak. It furnisiies the same facts as to the composi- 
tion and as to the physical properties of the intermediate feldspars, and, 
further, it has the advantage of explaining a mineralogical peculiarity 
as to which the theory of Tschermak is silent. 
The intermediate feldspars having a definite composition, here re- 
ferred to, are suscej)tible of physical as.sociation and the formation of 
compound crystalline bodies, but it should be noted that this is not a 
