692 WHITMAN CROSS 
chiquites is similar to eleolite-syenite in composition. The 
residual parts of any moderately basic rock, after crystallization 
of the ferro-magnesian constituents, will be identical with some 
possible extremely feldspathic rock. 
As for the question whether the colorless isotropic base of 
the so-called monchiquites is really glass or analcite it must be 
admitted that both are possible, although the former has not 
been proven in any special case known to me. The point raised 
by Pirsson, however, seems very important, namely, that as the 
monchiquites are supposed to be rather deep-seated dike rocks, 
it is much more reasonable to suppose that the residual substance 
would crystallize rather than forma glass. This argument has 
special weight where it can be shown that the residue has prac- 
tically the composition of analcite, and where associated rocks 
of the same or more silicious composition are found to be holo- 
crystalline. : 
The name analcite-basalt has been used for the rock here 
described because it accurately expresses its relation to allied 
types, because the name has priority over monchiquite through 
its use by Lindgren* for the rock of the Highwood Mountains, 
Montana, and further because the definition of monchiquite by 
Rosenbusch implies a glassy base, which is certainly a possibility, 
so that there may be rocks to which the name monchiquite 
applies in the sense originally proposed. It is probable that in 
many cases it cannot be demonstrated whether the colorless iso- 
tropic residual matter is glass or analcite, and where decomposed 
it will be clearly a matter of inference, in most instances. Criteria 
will doubtless be discovered by which analcite can be more readily 
determined than at present. The advisable course then seems 
to be to apply the name analcite-basalt where the determination 
can be rendered probable and to apply monchiquite in other 
cases. The fact that an analcite-basalt would have been a mon- 
chiquite if its residue had not cystallized shows the extremely 
close relationship of the two rocks. But it does not follow that 
*Eruptive rocks from Montana. Proc. Cal. Acad, Sci., Ser. 2, Vol. III, 1890, pp. 
39-57 (reference). 
