ON THE DETRITAL TIN-ORE OF CORNWALL. 229 
dykes (courses) which traverse both granite and slate,* and occur 
also in isolated masses, but these are peculiar to the granite ;—and 
bodies of felspathic and hornblendic rocks sometimes sever, some- 
times interstratify,t the slate. 
The granite, slate, elvan, and hornblendic rocks are all traversed 
by the odes; but on opposite sides of these the strata do not 
always occupy co-incident positions ;{ and the rocks as well as 
the Jodes are traversed by cross-veins.§ The lodes which yield ores 
of tin and copper usually bear a few degrees north of east and 
south of west,|| and the cross-veins (which are rarely productive 
at the intersections) range from north or north-west to south or 
south-east ;§ but where ores of lead and silver prevail the pro- 
ductive series usually-takes a nearly meridianal direction,** whilst 
the unproductive veins cross them.t{ Both Jodes and cross-veins, 
generally speaking—though with many exceptional cases—dip 
towards the nearest body of granite.tt} 
Tin-ore occurs in /odes which traverse§§— 
—the slate at Saint Neot, Saint Cleer, Linkinhorne, South Hill, 
and Calstock ;—and 
—the granite at Saint Cleer, Linkinhorne, Alternun, and South Hill. 
* Boase, Cornwall Geol: Trans: iv, p. 210. Dela Beche, Report, pp. 
180, 183. Giles, Cornwall Geol: Trans: vii, p. 201. Whitley, Geological 
Map of the Caradon Mining District. Holl, Quarterly Journal of the 
Geological Society, xxiv, pp. 415, 441. Henwood, Cornwall Geol: Trans: 
Viii, p. 670. 
+ Rogers, (Canon), Cornwall Geol: Trans: ii, p. 218. Boase, Ibid, iv, 
pp. 208, 220. De la Beche, Report, p. 79. Holl, Quarterly Journal of the 
Geological Society, xxiv; pp. 421, 444. Giles, Cornwall Geol: Trans: vii, p. 
205. Henwood, Ibid, viii, pp. 661, 701. 
~ Henwood, Cornwall Geol: Trans: viii, pp. 656-660. 
§ Ibid, viii, pp. 685, 714. 
|| Ibid, viii, pp. 674, 704. 
q Ibid, viii, pp. 681, 715. _ 
** Ibid, viii, p. 704. 
t+ bid, viii, p. 715. 
tt Ibid, viii, p. 675, 682. 
§ Copper and many of its ores are found 
in slate at Saint Neot, Saint Cleer, Linkinhorne, South Hill, and Calstock ;— 
in granite at Saint Cleer, Linkinhorne, and Calstock. 
Lead-ore is associated with silver 
in slate at Saint Pinnock, Menheniot, Saint Ive, South Hill, and Calstock. 
Native silver, and several ores of silver have been obtained 
in slate at Saint Pinnock, Saint Ive, and Calstock. 
