65 
the hornblende crystallizing out of it had a tendency to 
take up this element. 
The feldspar in the pulaskite, as has been mentioned, 
occurs in part as stout prisms and in part as smaller laths. 
The latter usually have a somewhat cloudy appearance 
under the microscope, probably owing to the incipient 
alteration. The larger feldspars are what is commonly 
described as soda-orthoclase. When examined under the 
microscope they are seen to be composed of very minute 
intergrowths of two, and in some cases perhaps even of 
three, different feldspars—causing them to present between 
crossed nicols a mottled appearance. These several 
feldspars have somewhat different indices of refraction, 
and frequently under a high power, where two are present, 
one of them can be seen to possess a very minute polysyn- 
thetic twinning, while the other is untwinned. The 
relative proportion of the several feldspars present differs 
in different grains. The individuals as a whole occasionally 
present the form of carlsbad twins, but usually have the 
appearance of simple crystals and consist of microcline, 
microcline-microperthite, with probably some anorthoclase 
The smaller lath-shaped feldspars, although more 
frequently composed of a single species, often show an 
intergrowth of two feldspars, as described in the case of 
the phenocrysts. Separations of the constituents of 
several species of the rock by means of Thoulet’s solution 
show that the smaller feldspars have a somewhat lower 
specific gravity than the phenocrysts, that is to say, the 
smaller feldspars approach more nearly to pure orthoclase 
in composition. No lime-soda feldspar can be recognized 
in any specimen of the rock. 
Nepheline and sodalite are quite subordinate in 
amount, although they are seen in nearly every thin 
section. Both minerals present the same characters and 
occur in the same way as in the essexite, lying chiefly in 
the corners between the other constituents, being pene- 
trated by the latter, but also occurring as inclusions in 
the feldspar. They are, as a general rule, much altered 
to the same decomposition product in the nepheline of the 
essexite and which is either kaolin or muscovite. Prob- 
ably both are present. 
Apatite is present in considerable amount and in the 
form of perfect crystals, occuring chiefly in the mica, 
hornblende and sphene. The iron ore and sphene present 
32224—5 
