XXIX 
(Country branches) of quartz than they are elsewhere. Such portions 
are frequently intersected by undulating joints, which—approxi- 
mately coinciding, as well with them as with similar divisions of 
the strata, in direction—divide them into subordinate veins of vari- 
able thickness. The faces of these joints,—like the faces of joints 
in the lodes,*—are often scored with unconformable strie. More- 
over they, not uncommonly, split into branches as well vertically 
as horizontally; and these sometimes dwindle, but frequently they 
reunite; occasionally also cross-veins are developed at certain 
depths only, and disappear both vertically and horizontally within 
very short distances. The cross-veins partake the nature of every 
rock,—and indeed of every vein—they traverse; and thus in 
granite—notwithstanding the occurrence of quartz at intervals— 
their principal ingredients are granitic ;{ and, when these are 
coarse and porphyritic, the crystals of felspar often assume some- 
what coincident positions ;§ in homogeneous slate, on the contrary, 
they, not uncommonly, consist of slaty clay, and then are called 
flucans ; || such parts of them—even when very soft—are, fre- 
quently of the same structure—whether fissile or thick-lamellar 
—and the planes of their cleavage incline at the same angles as 
in the adjoining (Country) rocks ;{ occasionally, however, both 
the slates and the cross-veins are, more or less, siliceous, and under 
such conditions small spheroidal masses—made up of quartz and 
of slate in alternating laminee—are, at rare intervals, imbedded 
in the latter ;** moreover considerable portions of many cross-veins 
consist of quartz, sometimes of massive character, but not un- 
usually crystallized in irregular prisms disposed horizontally, at 
right angles to the strike of the walls and joints.tt In the vici- 
nity of cross-veins, the rock is often thinly sliced by narrow strings 
of quartz.t{ Silver and copper together with many ores of both 
* Ante, p. 18. 
+ Henwood, Cornwall Geol: Trans: v., pp. 66, 89, 381. 
+ Ibid, v., pp. 257, 264; viii., p. 682. 
§ bid, viil., pp. 682-683. 
|| Phillips, (W.), Geol: Trans: ii., p. 134. Thomas, (R.), Report, p. 24. 
Carne, Cornwall Geol: Trans: ii., p. 107. Fox, Reports of the Royal Corn: 
Pol: Society, iv., p. 85. De la Beche, Report, p. 318. Henwood, Cornwall 
Geol: Trans: v., pp. 266. Von Cotta, Ore-Deposits, p. 407. 
q Henwood, Cornwall Geol: Trans: v., pp. 263-264, Tables xxxiv., 
Xxxvii., [xix. 
x« Tbid, p. 262, Table lxxxvii. 
++ Fox, Phil: Trans: cxx., p. 406. Reports of the Royal Corn: Pol: 
Society, iv., p. 89. De la Beche, Report, Fig. 62, 63, 64, 65. Phillips, 
(Prof.), Cabinet Cyclopedia, Geology, ii., p. 182. Henwood, Cornwall Geol: 
Trans: v., p. 261. 
tt Ibid, v:, pp. 257, 260, Tables lxix., xevi. 
