IGNEOUS ROCKS. 
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It is to be understood that the basis, or internal 
structure of that portion of the earth about to be 
described in a geological point of view, consists of 
that “ primitive” rock called Granite with a modi¬ 
fication thereof in two situations called Gneiss , and 
with Porphyritic characters in other spots, the 
whole passing ordinarily in the county under the 
term Moor stone, from its principal locality. Several 
geological reasons which I shall not be called upon 
to state here, induce the idea of this rock being al¬ 
most universally the nucleus of our globe, thougli 
we derive our chief acquaintance with it, from those 
elevations termed “ primitive mountains,” in which 
class rank the heights of Dartmoor, situated near 
the centre of our county, and constituting the in¬ 
cluded northern limit of the district, concerning 
which this work treats. But, not staying to adduce 
the variety of reasons for thinking that it exists 
generally beneath us in this county, I may, for the 
sake of perspicuity observe, that Dartmoor is not 
the only spot exhibiting granitic rock, or its modi¬ 
fications, but that on the contrary, it betrays itself 
to us in the Channel, as the Eddy stone and at the 
Bolt Head,* in an opposite direction re-appears in 
the hills near the northern coast, while, to the west¬ 
ward of the moor, granite has been found under the 
schist rock on the eastern bank of the Tamar, and 
in Cornwall formally exhibits itself in the character 
of hills, traversing the county to its south. Besides 
* The Channel Isles likewise, are in great measure granitic. 
