[ 2 77 ] 
the concave Part (for Inftance) of the Volitta of the 
Cornu- arnmonis be fet with Cryftals, their Points muft 
tend inwards to the Center, where the Tail ends, 
being thereto compelled by the regular Contour of 
the Shell 5 and indeed they are fo in Faff, as fee Fig. 
18. Tab. V. But if the Cryftal Juice chance to hx 
on, or proceed from a convex Bed (to which its 
Nidus , and other Caufes, may contribute), or be itfelf 
an orbicular Lump, and equally impregnated on all 
Sides $ then will the Fibres fpring as from one com- 
mon Center, and at their Extremities point forth 
their Cufpides in a circular Figure, as in Fig. 19 . * 
Tab. V. 
If there be a thin Plate of Spar equally expofed to 
Cold on each Side, and having equal Room and Force 
to (hoot, it will throw forth its Points on each Side ; 
and the Line from whence the Fibres began to fpring 
fha!l be exa&ly in the Middle of fuch Plate of Spar, 
and the Figures (halt cut the faid Line at right 
Angles, as in Fig. 8. Tab. IV. whence it feems rea- 
sonable to conclude, that the Dirc&ion in which thefe- 
fparry Produ&ions fhoot forth is generally re&angu- 
lar, or very near it, to the Beds or Mafles from which 
they proceed ; and that all the Teeming Confufion in 
Pointings of the Cornifh Diamonds in Pillion Erth, 
was owing to the great- Variety of Planes and Sur- 
faces, into which that large Body of Spar was harden- 
ing, when thefe Diamonds (hot from its Extremities. 
1 am , Sir , 
obedient Servant, 
Wm. Borlase. 
Ludgvan, Oct 18. Tour moft 
1749. 
* See Fig. 5. p. 261. 
XV. 
