230 The America?i Geologist. April, 1900 
structure and describes syenyte-aplyte, tonalyte-aplyte, dio- 
ryte-aplyte, nepheline-aplyte, etc.; moreover, he characterizes 
as aplitic dike rocks those of still more widely diverging chemi- 
cal and mineralogic composition, such as bostonytes, ting- 
uaytes, malchytes, and gabbro-aplyte or beerbachyte.* This 
structural use of the word aplyte has come to overshadow and 
obscure the mineralogic meaning. In a strict application, of 
course, the word must be used in one or the other sense and 
not in both. As a mineralogic term, therefore, it has been 
dropped in this classification. Moreover, even in its strictest 
mineral significance, it could not answer to the group name in 
the classification proposed, for this group name should em- 
brace granular hypidiomorphic rocks, and porphyritic rocks 
with coarse or glassy groundmass, as well as those with pani- 
diomorphic structure, and should characterize lavas or plu- 
tonic rocks as well as dike rocks. The structural use of the 
term aplyte is, therefore, fully retained in the classification, 
while, for the whole group of essentially quartz-alkali-feldspar 
rocks, the name alaskytet is proposed, and for the correspond- 
ing lava, (or the rock of any other habit, which has a porphy- 
ritic structure with a fine-grained or aphanitic groundmass,) 
the name tordrillyte J is proposed. The tordrillytes have gene- 
ral!)' gone in with the rhyolytes, but any set of analyses of rhy- 
olytes shows how much higher they run in silica than the 
granites. Those so-called rhyolytes which are unusually high 
in silica, would undoubtedly, if opportunity offered, crystallize 
as granite, alaskyte, and quartz veins, or simply as alaskyte; 
and so they are not the actual equivalents of ordinary 
granites. 
Alaskyte may therefore be defined as a group consisting 
essentially of alkali-feldspar and quartz, without other essential 
minerals. The group comprises all the holocrystalline va- 
rieties, and the mineralogic and chemical equivalents of these 
varieties, which possess other structures. Chemically the group 
is characterized by being exceptionally high in silica and low 
in iron and lime. 
*Op. cit., p. 491. 
tDerived from Alaska. 
JDerived from the Tordrillo mountains in Alaska, where it occurs as 
a dike rock. 
