ON THE DETRITAL TIN-ORE OF CORNWALL. _ 241 
series ;*—and that it is almost, or altogether destitute of tin-ore.} 
(V). The bed succeeding that which rests on the tin-ground presents 
a family likeness in neighbouring valleys; yet—even at a like depth 
its ingredients are not quite identical in all; indeed, different 
parts of the same vale—as, for example, at the sea-level and in 
the uplands present this (same) bed under very different aspects. 
It would seem, therefore, that, after the in-ground was de- 
posited, timber sometimes flourished in the lower valleys,{ whilst 
coppice and brushwood grew in and about the upland glens; and 
that some subsequent change in the relative levels of land and 
sea, affected the former,} without equally affecting the latter. §]| 
It would also appear that the deposit of barren débris was— 
* Maton, Observations on the Western Counties, i, p. 153. Hrnwoop, 
Cornwall Geol: Trans: iv, p. 61, Note; Ante, pp. 194, 195. 
{+ At Pentuan an arrow head and a small chisel of some extremely 
hard alloy, were found lying directly on the tin-grouwnd, at the bottom of an 
ancient shaft. Srocxur, Zransactions of the Penzance Natural History 
Society, ii, p. 89. 
“In process of washing the diamond-yielding (cascalho) detritus in 
“ Brazil, two lance-shaped arrow-heads,—one of petrosilex the other of rock- 
‘‘erystal—were obtained by H. von Helmreichen.” Journal of the Royal 
Geographical Society, xiv, p. 321. i 
+ Colenso, Cornwall Geol: Trans: iv, p. 32. Rogers, (J. J.), bid, vii, 
p. 354 
§ Henwood, /bid, iv, pp. 61—63; Ante, pp. 199, 200, 213,219, Table II. 
|| ** At Bovey Heathfield the lignite is overlaid by 
IRGEBo 000 00 00 Dod 00 DD0D DOD OO UODOO NOC Soadc0dD0000 « 0°5 foot thick ; 
Sand. Fine, white, quartzose .......-. eleloielelerererorte 3Ofeet ,, ; 
Clay and sand. In separate masses, but not dis- 6 
tinctly stratified ....... Jodou000000000000 } SSN 
Clay AMVC VAIL es Volatelelalejeleloherelererchelolelatevcleleie\elereislsteiers 10 uate 
Sandy clay. With angular and subangular stones. . thickness unknown, 
Nine feet below the surface of the plain we discovered a considerable 
number of dicotyledonous leaves in the white clay, and immediately below 
them lay some large roots.” Prnertty, Phil: Trans: clii, (1862), p. 1031, 
‘Of the diluvial species of plants several leaves lie upon the soft white 
“clay, which cannot be distinguished from those of Salix cinerea, Linn.... 
“The most frequent leaf of the white clay is Salix repens, Linn? Entire 
_ “little leaves, beside fragments of the leaves of Betula nana, Linn. have 
“been found in the white clay. Betula nana is a boreal plant, which is at 
‘home throughout the whole arctic zone; it is found also here and there 
“on the highland moors of Middle Hurope....In the British islands it occurs 
“in Scotland only.” Hauer, Lbid, pp. 1080—1082. 
