In the year 1888 I gave before the Mineralogical Society an account of the forms and optical characters of some minute crystals of kaolinite from Anglesey. At that time I was unable to ascertain whether the mineral was optically positive or negative, and it was stated that the axial angle 2V would approximate to 90°. Subsequently, by the aid of oil-immersion lenses and condensers of high angular aperture (numerical aperture=1.25), it was found that the mineral is optically positive and that the acute bisectrix is normal to the clinopinacoid (the obtuse negative bisectrix emerging through the basal plane). The optic axial angle in air was determined with an eyepiece micrometer to be 2E = 121°, with a possible error of one or two degrees, due to the small size of the crystals and the consequent weak interference-figures.