SECTIONAL TRANSACTIONS.—C. 313 
Mugearites. The differentiation series proceeds to the Trachytes, which 
apparently split into a more alkaline group of Phonolitic trachytes and a 
more acid group of Felsites. 
The major portion of the alkalic series can be interpreted as a result of 
crystallisation’ differentiation from a basaltic parent magma. The end- 
products (Phonolitic trachytes and Felsites) are probably due to the migra- 
tion (convection) of alkalies and volatiles. 
The members of the peralkalic series have resulted from an early gravita- 
tional differentiation (olivine sinking) together with the squeezing out of 
the residual liquid at the last stage of solidification (segregation veins of 
lugarite, analcite-syenite, etc.). 
The members of the calc-alkalic series are entirely due to the squeezing 
out of the residual liquid. 
The origin of the three principal series is explained by the migration of 
alkalies and volatiles in the primary basaltic magma, which itself is the 
source of the first series. "The upward migration of alkalies and volatiles 
probably occurred at the end of the volcanic period in consequence of the 
relief of pressure. The concentration of alkalies and volatiles in the upper 
zone of the magmatic reservoir gave rise to the peralkalic sub-magma, while 
the lower de-alkalinised zone produced the late calc-alkalic sub-magma. 
Dr. F. Waker. —A limestone-diorite contact near Dorback Lodge, Inverness- 
shire (11.0). 
The granite mass of Dorback to the north of the Braes of Abernethy 
exhibits a well-marked dioritic facies towards its eastern margin. This 
relatively basic rock is associated with a thick band of limestone which has 
apparently been caught up in the magma. While there is no evidence of 
extensive assimilation, a well-exposed contact in a stream section shows 
some interesting phenomena on a small scale. 
Analyses show that the diorite becomes richer in iron oxides, lime and 
potash towards the contact, while under the microscope hornblende is 
seen to give way to green diopsidic pyroxene. The limestone is richer 
in iron oxides and magnesia towards the margin, and this increase in 
ferro-magnesian content is accompanied by a greater development of lime- 
silicate minerals. 
The contact aureole of the granite contains some unusual mineral 
assemblages of which the most notable is a cordierite anthophyllite rock. 
Dr. R. Campse_t and Dr. I. M. Rosertson.—Glacial and interglacial 
deposits at Benholm, Kincardineshire (11.30). 
Near the farm of Upper Birnie, over 200 ft. O.D., and 13 miles from the 
sea, the drift deposits in the Burn of Benholm show the following succession : 
(a) Gravel, (b) Red boulder-clay, (c) Interglacial gravel, sand and peat, 
(d) Black shelly boulder-clay, with, at one point, stratified shelly sand and 
gravel intervening between the boulder-clay and the country rock. 
The shelly boulder-clay contains numerous arctic shells, usually broken 
and striated ; the boulders include chalk and other Mesozoic limestones, 
chalk flints, jet, etc. The included boulders indicate transport from the 
north-east. ; 
The interglacial sands and gravels are sometimes contorted. The peat, 
which has a maximum thickness of about 15 cm., shows several well-defined 
changes in structure and composition. The lower layers merging into the 
lower boulder-clay are black and well decomposed, and contain much silt. 
