PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 313 
On 25°01 grains— 

Silica, . J ; ; mat 259 
Alumina, : ; F egy boi 664 
Ferric Oxide, ‘ A : 3° 658 
Ferrous Oxide, : : a) poe old: 
Manganous Oxide, . : ‘ 4-468 
Lime, . 3 : : ? 4-116 
Magnesia, : , ; : 3° 464 
Water, . : é ; p * 32 
99-591 
Insoluble silica, 11° 602 per cent. ; probable impurity, quartz,—from which 
it was separated with extreme difficulty. 
6. From the summit of Meall Luaidh, north-west of Ben Lawers, Perthshire. 
Garnets of the size of peas lie loose on the summit of this hill in quantities, 
especially in the neighbourhood of a bed of yellow ca, | 
Their colour is a dull red brown. 
1-179 grammes afforded— 
Silica, : : : *419 
From Alumina, . : . 025 
"444 = 37°659 
Alumina, . } ; a. 24-803 
Ferric Oxide, : : ; 4:56 
Ferrous Oxide, . ; oa oie 
Manganous Oxide, : 2° 374 
Lime, . ; é : ‘ 5: 889 
Magnesia, 1-806 
100 - 064 
Insoluble silica, 11° 871 per cent. ; possible impurity, quartz. 
From Diorite. 
7. The rock from which the garnets now noticed are obtained I have never 
seen in situ; it is said to occur at the foot and to 
the north side of Knock Hill. 
Large loose masses of it I have observed on the 
summit of the cliffs on the east side of the Bay of 
the Durn,—to the east of Cowhythe Head,—and 
| near Retannach, in Banffshire. The rock, which is 
of a very fine grain, seems to be a labradoric diorite, 
| in which the hornblende is replaced almost entirely 
by a dark mica. Near Retannach it contains patches 

of snow-white granular labradorite ; elsewhere the whole rock is crypto-crystal- 
