20 
MUSEUM BULLETIN NO. 4. 
boulders in a three-foot stratum of analcite breccia. The matrix 
in which the boulders are embedded (field specimen 32) is 
composed of about 40 per cent bright flesh red analcite in icosite- 
trahedra! crystals up to an inch in diameter, usually beauti- 
fully regular in their crystal form, though often broken. Some 
crystals are worn nearly to a spherical shape, doubtless by water 
action. These analcites are embedded in a fine-grained, dull 
green matrix containing also a number of small dodecahedral 
melanite crystals. This tufaceous rock has probably a rathe^ 
similar composition to the magma from which it was derived, 
which magma is represented by the primary rock fragments 
now to be described. 
Blairmorite, variety A, consists of bright flesh red pheno- 
crysts of analcite up to an inch in diameter, evenly distributed 
throughout a dark olive green matrix, phenocrysts and matrix 
each forming half the volume of the rock. Rarely a light pink 
phenocryst of glassy sanidine is to be observed, and occasional 
small melanites are present. 
The red analcite greatly resembles garnet in the hand 
specimen, and can be distinguished from that mineral only with 
difficulty without microscopic or chemical tests. 
In thin section the rock is seen to be composed of pheno- 
crysts of analcite in a finely crystalline groundmass consisting 
of a second generation of analcite, gegirite-augite, nephelite, 
sanidine, and melanite, which are in turn embedded in an un- 
re solvable matrix, which may be incipiently crystallized analcite, 
gegirite-augite, etc. Calcite, and perhaps chlorite are the only 
secondary minerals noted. 
The large analcite phenocrysts are faintly pink, homo- 
geneous, and quite isotropic. Cubic cleavage is well developed, 
and faint, dust-like inclusions are seen along cleavage cracks. 
Narrow rims of clear analcite border most of the phenocrysts, 
and this feature is described later under Variety B. Alteration 
of these large phenocrysts is frequent, and consists of a replace- 
ment by calcite, this replacement starting along cleavage 
cracks and continuing until in some instances the whole 
mineral is replaced. 
