302 SECTIONAL TRANSACTIONS.—B, C. 
butter. A biological estimation of the vitamin A activity of such butters 
coupled with physical measurement of their carotene and vitamin A content 
permits of a calculation of the vitamin A activities of carotene and of vitamin 
A sensu stricto (joint work with Mr. A. E. Gillam of Manchester). 
When the chemical test for vitamin C (using the 2-6-dichlorophenol- 
indophenol reagent) is applied to bottled milk, marked day to day variations 
are noticed in the concentration of the reducing factor. These are due to 
the action of light transmitted through glass bottles. Vitamin C in milk 
is either rapidly destroyed by visible light or else it undergoes reversible 
oxidation, the product reacting no more with the vitamin C reagent. 
The vitamin D activity of butters is to a large extent lost after saponifica- 
tion, under conditions in which the antirachitic factors of cod-liver oil 
and irradiated ergosterol are unaffected (experiments on rats). The loss 
in activity is more marked in autumn and winter butters than in summer 
butters. 
Butter contains at least two factors of differing chemical stability, which 
are antirachitic for the rat. 
Discussion (12.30). (Dr. N. C. Wricur.) 
SECTION C.—GEOLOGY. 
Thursday, September 6. 
THE GEOLOGY OF THE ABERDEEN DiIsTRICT (10.0) :— 
Prof. A. W. Giss.—Solid geology. 
Dr. A. BREMNER.—Surface geology. 
Mr. C. B. Bisset, Dr. S. BucHan, Miss Jean E. ImMuay, and Mr. J. A. 
RoBBIE.—On some granites of Aberdeenshire (11.15). 
It has hitherto been assumed that the grey granites of Aberdeen are of 
Older or pre-Torridonian age, while the red granites of Hill of Fare and 
Bennachie are Younger or Caledonian. 
It is now suggested that the majority of the Aberdeenshire granite masses 
are of Caledonian age. ‘Two divisions are recognised—an Earlier and a 
Later. 
In the Earlier Caledonian group are the Skene complex, the Aberdeen, 
Garrol and Cairnshee granites. ‘This group contains a series of rocks, 
which show a graded transition from a spheniferous quartz-mica-diorite 
through hornblende-granite and porphyritic biotite-granite to grey, two- 
mica, microcline-granite. A transition between the Skene and Aberdeen- 
shire granites takes place by diminution of porphyritic character, alteration 
of phenocrysts from perthite to microcline, appearance of muscovite and 
change of colour from red to grey. Mr. Bisset has recorded that the evidence 
points to variation of rock-type being due to differentiation. 
The Hill of Fare, Bennachie and Peterhead granites make up the Later 
group. ‘This consists mainly of coarse, non-porphyritic, more acid, red, 
biotite-granites. Within the mass there is also variation. Coarse granite, 
rich in heavy minerals, has been intruded before finer, more acid granite 
in which the heavier minerals are scarce. Dr. Buchan notes that a grano- 
diorite locally developed is due to interaction of granite and country-rock, 
while grey granites arise from reaction between red granite and mica-schists. 
