228 JOURNAL OF THE PLYMOUTH INSTITUTION. 
tourmaline. A detached block near the base of the Tor bears 
much the same aspect. The same green and brown hornblende is 
present, with lath-felspars, patches of ilmenite, and a little augite, 
as well as diallage. Both these rocks are dark-grey; black when 
polished. A slide cut from a small nodule of the rock, apparently 
a contact specimen with the granite of Brazen Tor, is mainly 
pale-green hornblende with plagioclase-felspar, and opaque grains 
and crystals, probably ilmenite and magnetite. The Lydford 
rock much resembles that of White Tor—the green hornblende 
well marked, a little brown, and porphyritic crystals of orthoclase 
felspar. . 
The nearest approach among our local rocks to the diorites is in 
this group. 
Hornblende-Schist—Rocks which may be classed under this 
head, though of varying character, occur, chiefly in connection with 
the gabbro, at Waspworthy, Cocks Tor, Smear Ridge, Peek Hill, 
Houndall, and Ivybridge. Mr. Rutley describes the amphibolite 
of Waspworthy as consisting of quartz, pale-brown hornblende, 
and pyrites. A section cut from a specimen collected at the same 
spot, and having the same outward appearance, shows, however, 
in addition a number of lath-crystals of felspar. Probably there 
is considerable variation in a small range. The Houndall rock 
in external appearance much resembles this, but the felspars are 
less prominent, and the pyrites and hornblende are more abundant 
and more regularly distributed. The lamination in these two 
rocks is not distinct, as a rule, but in the Ivybridge example it is 
much clearer. Under the microscope the hornblende, which is in 
very small patches and flecks, is seen to closely resemble that at 
Waspworthy, but the quartz foliations are much more pronounced, 
Contiguous to both the Peek Hull and Ivybridge rocks is a 
green banded rock, commonly called ‘“ribbon-jasper,” between 
the schist and the granite, and apparently jaspidized by the action 
of the granite on the schist. Under the microscope it is seen to 
consist of quartz and a green dichroic mineral, which partially 
resolves itself, under higher powers, into delicate green-bladed 
crystals of actinolite. The rock may be described as consisting 
of laminations of ordinary quartz and prase = prase-schist. There 
is some evidence that here we have a result of a double change ; 
first, the conversion by pressure of a dolerite into hornblende- 
