OF CORNWALL. X S 7 
die, and contracting gradually at each end ; black, fmooth, fhining 
as glafs, 
Fig. vi. A very large grain of tin ; the prifmatic ridges in which 
this metal delights, are here placed nearly at right angles. It has 
a fmall rhomboid plane at the point of infertion where the ridges 
meet at e ; but where the fides of the two ridges fhould meet, as 
at f fi they are there planed off. 1 he largeft tin-grain I have yet 
feen. 
vii. The furface of this grain is divided into eight triangular - 
planes, fo applied to one another as to conftitute four ridges meet- 
ing in a fmall central fulcus. This figure is very rare, and the planes 
of a high polifh. 
vm. A columnar grain on a rhomboidal bafe. 
ix. D . more diftindt, the apex a quadrilateral pyramid. 
X. A bunch of tin-grains, connected as if one large grain with 
its furface differently fhot. The figures are pyramidal and cuneoid, 
three of the latter fpread like the toes of a bird from the point of 
contact. 
xi. An equilateral triangular plane projecting from a parallel 
ground, edged on one fide with a quarter-round bead parallel to the 
adjoining fide of the triangle. 
xii. A pyramidal pentahedral grain perfectly fmooth and black ; 
its front confiffs of two unequal equilateral triangles, divided by a 
fulcus ; of the other faces of the pyramid, two are cuneoid, the 
other circular. 
xm. Plan of the foregoing pyramid, N°. xn. 
xiv. A quadrilateral, irregularly -pyramidal grain. The two 
ends are cuneoid, the two fides defcend from the apex in a flope, 
ftriated to the bottom, where the fries fpread off in an obtufe an- 
gle, as if defigned to form another pyramidal procefs of like ftruc- 
ture on each fide. 
xv. Another of like form, but more finifhed in figure, and of 
a higher polifh. 
xvi. A plan of a quadrangular pyramid on a column of a nearly 
fquare bafe ; one face of the pyramid is divided into two nearly 
equal triangles by a fubfidence in the middle, approaching fome- 
what to N°. vn. 
xvn. The elevation of N°. xvi. 
xvm. Grain-tin melted, firft in the common way, then farther 
purified, as far as the prefent method will permit. 
xix. A, the front, and B (by fcale annexed) the back-view of 
an ancient block of tin, explained before, page 163. 
xx. A curious grain of tin, black and fhining, with flammulce of 
a golden colour ; the faces pentahedral ; but the greateff rarity of this 
fpecimen 
