Vol. 58.] THE MINERAL ANALYSIS OF ROCKS. 169 
Skye Gassro No. 8043. GazBro No. 8194. 
Calculated. Found. Calculated. Found. 
(Solias.) (Pollard.) (Sollas.) (Pollard.) 
DIOR eee Seat. 47-81 46°39 47°81 47°28 
HOY 3. Pastas oo i.e trace 0:26 —- 0:28 
JT. 0 eines 24-21 26°34 21-02 21-11 
SOs (i655 Se trace = 
JG 0 Pecerme cena 2-48 2°02 2-21 3°52 
159 Is eee eee 2°84 3°15 4-44 3°91 
J. 571 0 eerie gf 0-14 0-13 O15 
J. 0 en 349 4:82 DLO 8:06 
CAO .cneet 15°84 15°29 17-17 13°42 
Na O) Eo Re eens 2°07 1:63 1°50 1°52 
1 ORE eee re 0-40 0:20 0:15 0:29 
1540 eee er 0°86 0-58 0:47 0°66 
1240 = he ene sth trace ars trace 
100°00 100°82 100-00 100°20 
erases aang 
No doubt the close approximation between my results and 
Dr. Pollard’s, especially in the case of specimen 8194, is to some 
extent due to the predominance of felspar in these rocks, and to 
the fact that the analyses of minerals from which I calculated the 
composition had been most of them made on Scottish examples. 
The mineral composition of the two rocks was determined as 
follows :— 
GapBro 8043. Gaxspro 8194. 
Sp. gr. Per cent. Sp.gr. Per cent. 
Labrador-felspar ...... 2°735 to 2°7 79°50 2°737 65°96 
Pyroxene (oblique)...... 3°21 to 3°335) =: 16°18 3:280 32°43 
Pyroxene (rhombic) ... 3°40 2°10 — 
Maemetite a7 s.2)s. onan 2°40 1-61 
100°18 100-00 
Some time ago I worked out the mineral composition of the 
Leinster granite by the laborious process of weighing areas of 
the sections of the component minerals as observed in thin slices, 
and it now occurred to me that it might be of interest to apply 
the new method to an investigation of Cornish and Skye granites, 
in order to obtain material for the comparison of these various 
granites in regard to their mineral composition. This could scarcely 
fail to be of interest, owing to the fact that these rocks represent 
granites of Tertiary, and of approximately Permian and Silurian 
age. The Cornish granite was studied by Miss Davies in my 
laboratory ; she obtained the following results :— 
Sp. gr. Per cent. 
Oiuthoelase. ray sates sctsass Pema 2°560 24°62 
TONE Ciyga st oe ye eee pe ez, 2°624 13°44 
AES ISD see PRS ER 2-645 40°23 
UIRCOVIEE soe: 135 apiane adv aitiacinss 2°825 10-09 
IBLOEILEY rere gamer ae Pe aa: 3°065 11°46 
Magnetite and zircon ............ ot 0°16 
« _ 100:00 
