THE ROCKS OF PLYMOUTH. OO 
ceptional lasting qualities. The quarries here are the most 
important in this immediate locality. A grey granite has also 
been quarried at Shaugh, in which tin ore is_ occasionally 
disseminated. Happily, however, the Dewerstone quarries are no - 
longer worked. Much granite has been wrought from the loose 
blocks on the surface of the Tors, and no little injury done to 
their picturesqueness in the process. Pew Tor has in this way 
been somewhat extensively worked. The granite here is a warm- 
grey porphyritic variety, a good deal of the felspar having a 
granular aspect. There is black mica and a notable proportion 
of schorl. 
Granite worked at Ivybridge is bluish-grey, compact, and even- 
textured, with porphyritic felspars, a little schorl, and black mica, 
Lustleigh yields an even-grained bluish-grey variety, containing 
black mica, with porphyritic development of lath-shaped felspars 
and quartz. At Stone Tor, near Chagford, there is quarried a 
compact, close-grained porphyritic granite much resembling this. 
Associated with the Chagford granite are some dark-grey nodular 
segregations, which, as Mr. J. A. Phillips has shown, are essentially 
a fine-grained phase of the rock in which they occur, 
Coarse varieties of grey granite are to be found on almost 
every Tor, especially near the edge of the granitic area. The 
Staple Tor granite, with large crystals of felspar and an abundance 
of black mica, affords a very good illustration. Very coarse- 
textured porphyritic granite also occurs near Princetown. The 
mica is black, and the felspar much decayed. From the size 
of the quartz and felspar crystals this may be ranked as “ giant- 
granite.” It has, however, interstitial fine-grained granitic 
patches, which give it a distinctive character, and is thus really 
granite porphyritically developed in a semi-crystalline granitoid 
ground mass. Not infrequently the ordinary granite is traversed 
by veins of much finer grain, which do not seem the result of 
segregative action, but of subsequent origin, the division lines 
being distinct, and the intrusive character plain. 
The finest-grained granite rock that I am acquainted with on 
the south-western side of the Moor—and one that may fairly bear 
comparison with the white granite near Okehampton, of which 
De la Beche speaks as rivalling statuary marble—occurs near the 
Devil’s Bridge. It is of the most even granular texture, mainly 
white felspar with delicate needles of schorl, mica as an essential 
