176 . General Notes. [ Feb. 
under which they solidified have varied to such an extent, in 
consequence of differences in the thickness of the dyke, in 
the depths at which pos portions crystallized, in the degree 
of conductivity of the S pricama Pe that all types of 
- structure are found i em. s t be expected, this 
class is much less well defined than tliat. of the intrusive rocks 
later. In it are included only those rocks which can neither be 
regarded as intrusive nor yet as effusive. They are divided 
according to structure into three distinct types, — aes the granitic; 
, the grano-porphyritic; and, III., the lamprophyric. They 
all tend to the development of one or ‘the other of their constitu- 
ents in porphyritic crystals; in other words, they are all panidio- 
hic. 
The granitic class includes only aplite and beresite 
The structure of the grano-porphyritic type is defined by the 
name. They are porphyries in the sense that they contain certain 
of their ingredients in two generations, but differ from them in 
e possession of a holocrystalline ground-mass. Among the 
grano-porphyritic class are placed granite-porphyry, syenite-por- 
phyry, eleolite-syenite-porphyry, diorite-porphyrite, and quartz- 
diorite-porphyrite. It will be seen that this class embraces most 
oen those pre-Tertiary porphyritic rocks that are not true porphy- 
ge lamprophyres are distinguished from the grano-porphy- 
ritic group by the prevalence of bisilicates and the subordination 
of the feldspathic constituents. They consist of a fine-grained 
to very compact (dicht) ground-mass, in which porphyritic crystals 
of biotite, augite, or hornblende are scattered. They all weather 
very readily, and, as a consequence, pea a great deal of cal- 
cite, so that in many cases before their structure can be studied it 
is necessary to etch their thin sections with a dilute acid. 
The lamprophyres are subdivided into the syenitic and the 
dioritic varieties. The syenitic varieties include minette, charac- 
terized by the e predominance of biotite, and vogesite, in which the 
place of the biotite is taken by hornblende or augite. The 
dioritic varieties embrace kersantite and camptonite. The latter 
name is applied to the porphyritic diorites described by Hawes * 
from the neighborhood of Campton, N. H. They contain por- 
phyritic brown hornblende and lath-shaped plagioclase crystals 
in a ground-mass composed essentially of green augite, apatite, 
1 i i i exist. 
id : | y 
The third and last great class of rocks is that of the effusives 
(Ergussgesteine). It embraces those which were poured out 
-~ „upon the surface and then solidified . They are found in sheets 
~ and in volcanic streams (Decke and Ströme). There seems to be 
aeons kA should not be a corresponding effusive rock 
*Minenlegr 408 Leber os emo, 1878, p. 160. 
