Reports and Proceedings—Mineralogical Society. 233 
II.—Mrneratoercat Socrery. 
March 15, 1910.—Professor W. J. Lewis, F.R.S., in the Chair. 
G. W. Grabham: A new form of Petrological Microscope, with notes 
on the illumination of microscopic objects. The new instrument, 
which is of the ‘Dick’ or ‘ English’ pattern, has a focussing sub- 
stage carrying a series of condensers mounted on a triple nose-piece, 
each capable of being inserted in the axis of the instrument. A new 
explanation was given of the ‘ Becke’ or bright-line effect, especially 
applicable to parallel polarized light traversing mineral sections which 
meet along inclined junctions.—W. F. P. McLintock: On Datolite 
from the Lizard District. Datolite, which is associated with calcite, 
chalcopyrite, and natrolite (rare) in veins and geodes at the junction 
of the serpentine and hornblende schist, Pare Bean Cove, Mullion, 
Lizard District, Cornwall, occurs in crystals measuring up to 2cm. 
along the 6 axis, and displayed fourteen forms, of which two were new. 
An analysis gave SiO, 37:45, CaO 84°67, Fe, 0, and Al, O03 0°57, 
B, O, 21°87, H,O 5°67; total 100-23.—Arthur Russell: Additional 
notes on the occurrence of Zoolites in Cornwall and Devon. The 
occurrence of heulandite, a mineral hitherto not recorded from 
Cornwall, at Carrick Du Mine, St. Ives, Cornwall, was described ; 
also of chabazite and heulandite at the Ramsley Mine, South Tawton, 
Devon.—Dr. J. W. Evans: A modification of Stereographic Projection. 
Faces below the plane of projection are represented by the same points 
as parallel faces above it, upper faces being distinguished by a plus 
and lower faces by a minus sign.—Dr. J. W. Evans: Axes of Rotatory 
Symmetry. Coincidence is complete or codirectional when equivalent 
lines and their directions coincide, incomplete or contradirectional 
when equivalent lines coincide, but equivalent directions of uniterminal 
lines are opposed ; in both cases it is colinear. Ifa minimum rotation 
20 . ; : é 5 : ee 
of — result in codirectional, contradirectional, or colinear coincidence, 
the axis of rotation has codirectional, contradirectional, or colinear 
symmetry, with cyclic number x.—Professor H. L. Bowman exhibited 
models illustrating space-lattices and Sohncke’s point-systems. 
CORRESPONDENCE. 
THE USE OF THE TERMS ‘LATERITE’ AND ‘BAUXITE’. 
Srr,—Mr. Scrivenor’s further remarks on this subject in the March 
number of the GroLocicaL Magazine, replying to mine in the number 
for November last, bring into sharp relief some of the difficulties 
which he and others experience with regard to the recognition and use 
of ‘laterite’ as a scientific term. I for one am not unaware of these 
difficulties. Indeed, I perceive one or two which are in my opinion 
more serious than those mentioned by Mr. Scrivenor. At the same 
time, all these difficulties taken together are small compared with 
those which prevent us from adopting the use of the mineralogical 
term ‘bauxite’ as a rock name. Furthermore, surely the fact that 
some engineers—and, alas! some others—have abused the term laterite, 
