PRIMARY ROCKS. 
219 
shte constitute the chief rocks in the primitive 
formations. Doubtless the most simple classifica- 
tion of primitive rocks is into unstratijied and strati- 
fied ; including under the foxmev granite, syenite^ 
porphyry, and greenstone, and perhaps granular lime- 
stone, all of which probably owe their origin to ig- 
neous causes ; while the latter would embrace 
gneiss, mica slate, argillaceous, talcose, and chlorite 
slate, quartz rock, &c., which have been produced by 
the consolidation of the particles resulting from the 
disintegration of the igneous rocks, and in some in- 
stances of that of the quartz rock, modified by sub- 
sequent heat. At any rate, few geologists of the 
present day, or perhaps none who deserve the 
name, can be found who will deny a belief in the 
igneous origin of the unstratified rocks, and who do 
not regard them as merely varieties of the same 
melted mixture, whose peculiarities resulted from 
the modes in which they were cooled and crys- 
tallized, and included among the stratified rocks. 
It by no means follows, from this view of the sub- 
ject, that all the unstratitified rocks are of the same 
age, as they were doubtless protruded at different 
periods. Granite veins have, for example, been 
found overlying chalk ; basalt has cut through 
rocks of every formation ; and lava every day over- 
spreads diluvium and alluvium. 
Professor Hitchcock speaks of a pseudo-stratifi- 
cation of granite in Worcester ; but this is doubtless 
to be attributed to the process of cooling, under pe- 
culiar circumstances of position, as we see in ba- 
salt ; it sometimes assuming a columnar form, at 
other times not. Throughout New-England granite 
usually occurs in the form of veins and protruding 
masses, sometimes lying between the strata of 
other rocks, but rarely, if ever, overlying them. 
Professor Hitchcock gives numerous instances of 
such veins in mica slate, hornblende slate, gneiss, wi- 
caceous limestone, &c. Such veins abound in the 
