O48 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
siliceous and more highly calcareous lodge in the lime; the more siliceous and 
less calcareous in the including rock. 
There can be no room for doubt that these minerals are the results of an 
exalted metamorphism, which has resulted in a direct. combination between the — 
‘constituents of the gneiss and the limestone. 
One of the many species which are to be found lodging i in the intermediate — 
zone of rock is andesine, and it is to be found of three appa it might 
almost be said in three conditions. 
In all these it presents itself in large crystals, sometimes over two inches in — 
length and breadth, by one-third of an inch in thickness. Of these crystals 
some are readily cleavable, clear, translucent, lustrous, and of a blue-white — 
colour; they are simple twins, but not striated; others of the crystals are 
duller, opaque, and cream-coloured; they are, however, distinctly cleavable ; 
while, lastly, some have a slightly cape -white colour, a minutely granular 
structure, no cleavage, a glimmering lustre, and they present vacuities studded 
with minute crystals, which pass into a granular structure; these last. are, 
in fact, pseudomorphic, and the material is Prehnite. In one and the same — 
crystal a distinct transition may be seen from the second to the third. 
When Prehnite replaces andesine, there must—according to the law of 
pseudomorphic interchange, as laid down at page 506 of vol. xxvii. of these 
Transactions, and calculated out as regards this particular case at page 510— : 
be a vacuity equal to the difference between the numbers 686 and 795—about — 
one-eighth ; hence the vacuities in the pseudomorphosed crystal. 
The blue lustrous crystals gave a cleavage angle of 86° 21’; the white some- — 
what massive variety, was curved on the cleavage faces ; the specific gravity of — 
the first was 2°705, of the second 2°689. For comparison, the analyses are 
placed in juxtaposition. There would appear to be in the second an incipient 
transition into the Prehnite, the analysis of which is appended to exhibit this. 
The crystals were not striated. . 
_ The Blue, The White, The Prehnite, 
on 1'651.grm. on 1°623 grm. on 1°51 grm. 
Silica, ey hohe 56° 961 44°105 
‘Alumina, . , . 24°042 23°81 22: 568 
Ferric Oxide; . . 1°124 * 938 2°894 
Magnesia, . ch Nd MEER - 086 *529 
Lime, =, 6 105 7°984 - 25 +478 
Potash, ce . 2° 832 2°565 ops 
Soda, ; ‘ J od PloZ 6° 853 tr. 
Water, 1°596 1°621  4:°604 
100°129 100: 814 ; 100°178 
Insoluble silica, 9:11 per cent. 

