ON THE DETRITAL TIN-ORE OF CORNWALL. 245 
—like lead-ore in the north of England,*—native copper on the 
shores of Lake Superior,|—and gold in the mountain-cascalhot 
of Brazil,—it has occurred—and, to some trifling extent, still 
occurs—in, more or less, abraded masses on the slopes of many 
hills ; and this so frequently that, during early periods of Cornish’ 
mining industry, they were—and, indeed, to some extent, they 
still are—traced as guides to the lodes whence they had been 
riven. Such transported masses, however, are limited to slopes 
in no particular direction ; but owing to the contour of the surface§ 
and the general directions of the Jlodes,|| they have been more 
numerous on the northernf and southern than on the eastern and 
* “ Shoad ore is a pretty sure indication of a vein where it is found, or 
‘‘a little above, or higher on the acclivity of the surface ; but you must judge 
‘“‘of the distance above, by the greater or less acclivity of the slope....The 
“‘shoad ore is found...in rough irregular globes...of all sizes, from very 
‘large masses, down to the size of peas, and smaller grains,...and is fre- 
“quently coated with white on the outside....Float ore differs from the 
“ shoad; the former being water-worn, the latter not. The float ore is 
‘generally mixed with water-worn bullets and gravel; the shoad never, 
“unless it has been washed off the superficies of the vein by some stream 
‘‘of water.” Forstrer, Section of the Strata between Newcastle and Cross 
Fell, pp. 276—278. : 
+ “Ten leagues south of Lake Superior there is a single lump of native 
‘“ copper about four tons weight... but no vein of copper has been discovered” 
‘‘ Tin the neighbourhood.] Prycr, Mineralogia Cornubiensis, p. 61. 
“Tt is well known that transported masses of native copper are occa- 
“sionally met with in the diluvial deposits which are abundantly spread 
‘over the country...south of Lake Superior.” Houauron, Silliman’s 
Journal, xli, p. 29. 
“ Fragments of metallic ores and native copper,—the latter sometimes 
‘“‘weighing several hundred pounds...occur oceasionally...in a layer of clay 
‘‘resting either on coarse drift or...on the rock.” Fosrzr anp WHITNEY, 
Report on the Geology of Lake Superior, pp. 186—191. (Abridged). 
“‘ About [1864] two years since [a mass of copper] which weighed about 
“eighteen tons was found loose on the drift covering the rock...near Portage 
“Lake.” BavErman, Quarterly Journal of the Geological Society, xxii, p. 452. 
i “There is a difference between the cascal/ho in the mountains and 
‘“‘that in the rivers; the embedded stones in the mountain-cascalho are 
‘rough and angular, but in that of the rivers they are rounded.” 
MAaNoEL FERREIRA DA Camara, (Southey’s), History of Brazil, iii. p. 827. 
§ De la Beche, Report, pp. 19—20; Fig. 1. Ante, pp. 233—235. 
|| Henwood, Cornwall Geol: Trans: v, pp. 250—254, Pl. xi, Fig. 5, 
Table ciii; Ibid, viii, p. 674, Note+; Journal of the Royal Institution of 
Cornwall, iv, (No. xiii), p. xvi; Annales des Mines, 7me Serie, ii, p. 172. 
q An instructive example of shode-tin-ore has been lately discovered by 
the Reverend William Borlase, M.A., Vicar of Zennor, in the ravine which 
bounds his glebe, and within gun-shot of the Bristol Channel. 
