382 HENRY S. WASHINGTON 
while not very numerous, are yet significant, and which may be referred 
to two kinds: those which are modally free from leucite, though they 
contain it in the norm, the abnormality being explicable, in part by 
the incomplete crystallization, and in part by the mass effect of the 
complex minerals present in abundance in these rocks, and _ their 
comparative paucity in potash; and those whose modes contain 
abnormative leucite, either showing none of this in the norm, or 
containing modally more than exists normatively, these cases being 
explicable by the early crystallization of soda-lime feldspars (due 
either to the superior affinity of lime for soda or to the great tendency 
toward crystallization of these feldspars), and of soda-orthoclase or 
analcite which may crystallize either prior to or at the same time as 
the leucite. 
In both classes of exceptions the conditions of solidification seem 
to have a determining effect, those obtaining in effusive rocks favor- 
ing, and those in intrusive rocks deterring, the formation of leucite. 
A few exceptions, which cannot be explained by any of the sup- 
positions made above, remain to be discussed. The first is the so- 
called leucite-granite-porphyry of Brazil, described by Hussak,? 
which consists of large phenocrysts of pseudo-leucite in a fine-grained 
groundmass composed of orthoclase and quartz, thus apparently 
forming an exception to the otherwise invariable incompatibility 
of quartz and leucite. This highly anomalous occurrence is explained 
by Hussak (loc. cit., p. 26)as the result of a “granophyric’”? magma 
breaking through a leucite-foyaite or leucite-tinguaite; and_ this 
explanation may reasonably be accepted as the true one. 
The only other exceptions which need be discussed are the wyoming- 
ite and the orendites of the Leucite Hills (Nos. 104, 105, 106), which 
carry abundant modal leucite and whose loci fall within their leucitic 
area, though they do not show either leucite or nephelite in the norm, 
and even in one case have normative quartz. These rocks, further- 
more, have an excess of alkalies-over that needed for feldspar and 
acmite, resulting in the presence of sodium and potassium metasilicates 
inthenorm. The peculiar features of these rocks have been discussed 
by Cross,? who shows that they cannot be due to errors of analysis, 
1 E. Hussak, Neues Jahrbuch (1900), Vol. I, p. 22. 
2 W. Cross, American Journal of Science, Vol. IV (1897), pp. 131-34. 
