312 SECTIONAL 'TRANSACTIONS.—C. 
Wednesday, September 12. 
Mr. A. T. J. Dottar—The petrology of certain dike rocks of high 
magnetic susceptibility (10.0). 
In 1933 relatively large magnetic anomalies were detected while making 
traverses above basaltic and doleritic dikes hidden beneath an overburden 
of 9 in. to 10 ft. of soil on Lundy, Bristol Channel. 
Samples of these dikes were collected and examined petrographically 
by the author, while the magnetic mass-susceptibilities (i.e. the respective 
magnetic susceptibilities per unit volume—measures of the magnetising 
effects of particular magnetic fields upon specimens placed in them—divided 
by the respective densities of the specimens ; both sets of quantities being 
expressed in appropriate units) of (a) small rectangular bars of square 
cross-section, cut from these rocks, and (b) powdered samples of the same, 
were determined by Prof. E. Herroun, using a modified Curie balance and 
magnetic fields of suitable strengths. 
The numerical values so obtained prove to be related in an interesting 
manner to (a) the kinds, proportions and distributions of iron-bearing 
minerals in the dikes, especially magnetite, hematite and ilmenite ; (0) states 
of weathering in the rocks; (c) magmatic differentiation, including the 
sorting of iron-rich minerals by convection currents ; (d) directional mag- 
netic properties acquired in the earth’s magnetic field, or as a result of 
conducted lightning discharges ; (e) data obtained from magnetic measure- 
ments made with the vertical magnetic force variometer. 
The unusually high value of 4230 X 10-°c.g.s.u. for the magnetic volume- 
susceptibility of a sample from dike’ No. 21, East Side, Lundy, using a 
magnetic field-strength of 78 c.g.s.u. in the measuring instrument, is 
especially noteworthy in relation to the character and content of its iron- 
bearing constituents. 
Mr. S. J. Tomxererr.—The British Carboniferous-Permian igneous province 
(10.30). 
Statistical methods are applied to the study of the late Paleozoic igneous 
rocks, mainly in the midland valley of Scotland and the Borders. The 
material comprises 254 chemical analyses (recorded and unrecorded) and 
126 modal analyses (including 80 new analyses). 
According to relative age the rocks are divided into the following series : 
1. Alkalic series —Olivine-basalts, Mugearites, 'Trachyandesites, 
Trachytes, Felsites. Mainly lavas of Lower Carboniferous age. 
2. Peralkalic series—Picrites, Picro-teschenites, Teschenites (Theral- 
ites), Lugarites, with a transitional series of Basanites, Crinanites, Essexites. 
Late Carboniferous or early Permian intrusives. 
3. Calc-alkalic series —Quartz-dolerites with segregation veins. Prob- 
ably early Permian intrusives. 
The modal analyses refer mainly to the olivine-basalts, which, although 
forming a continuous series, can be subdivided into three groups according 
to the relative proportions of pyroxene and feldspar (olivine and iron ores 
do not show any significant variation) : 
(1) Pyroxene-rich group—Hillhouse and Craiglockhart types. 
(2) Intermediate group—Dalmeny and Dunsapie types. 
(3) Feldspar-rich group—Jedburgh and Markle types. 
The first group grades into the Basanites (including monchiquites, etc.}, 
while the third group passes into a more acid and amore alkaline group of 
