97 



MINERAL RICHES OF OUR VICINITY. 



Continued and concluded from page 70. 



5. Trapp forms entire mountains of almost pure 

 hornblende. Such is White Tor, on the west of Ta- 

 vistock, and part of Cock's Tor, the first hill of the 

 Moor on the Tavistock side. Good crystals of horn- 

 blende may be occasionally found in these hills. 

 Where this trapp comes in contact with slate, the latter 

 is sometimes converted into a beautiful substance re- 

 sembling ribbon jasper. Fine specimens of this sub- 

 stance may be found on the western foot of White 

 Tor, and on the side of the hill, near Ivy Bridge, which 

 is capped with the " Race house/ 7 A few mines have 

 been opened on the north of the Moor, at this line of 

 junction ; and from these are obtained garnet, axinite, 

 pseudopal, in some cases so near resembling real opal 

 as not to be immediately distinguished from it. Whether 

 the same substances exist under similar circumstances 

 nearer home, will be better known when more attention 

 shall have been paid to these rocks both by the mineralo- 

 gist and the miner or quarryman. Another variety of 

 trapp, greenstone, contains also felspar; and, in a 

 quarry of it, on the Rail Road, asbestos and epidote 

 are found. The writer has seen a specimen of epidote, 

 from that quarry, covering a surface of more than a 

 square foot, and in regular crystals throughout. 



6. Slate. This rock forms the greatest part of the 

 country, for many miles round us ; and, in itself pro- 

 duces little of any interest to the mineralogist. But 

 our slate not only passes into greywacke, (usually 

 called "dunstone,") in various parts ; but is also inter- 

 sected by veins of quartz, felspar, trapp, and some 

 other rocks of a more compound nature : and at these 

 points good specimens not unfrequently occur. Of 

 the trapp intersections notice has been taken above. 

 Where porphyry or compact felspar is the intruder, 

 some modifications of the latter sometimes occur ; and 

 Mr. Phillips found a chiastolite (a rare mineral) near 

 such a point, in the road from Ivy Bridge towards 



VOL. in. 1834. o 



