Much study has been bestowed, upon the boulders included in the Glacial Clays, their nature, origin, and distribution. The matrix in which they lie has received comparatively little attention. Yet the matrix, in many or most, forms by far the largest part. I have been endeavouring to study this matrix under the microscope, by washing it, shaking it up with water, and so separating the material which will settle quickly to the bottom from that which remains longer in suspension. The process has to be repeated until the water remains clear, else dust still suspended dries on the surfaces of the grains which had settled and masks them from examination. I have collected and dried this finer dust, but it cakes together: I have not obtained from it much information. The coarser material, that which subsides first, forming from 40 to 75 per cent. of the whole, dries to a sand or powder and lends itself readily to examination with the microscope. I have tried several methods, and have succeeded best by inspection under direct daylight of the powder strewn on a slide. Inspected in this manner, Glacial Clays from localities in East Anglia tell something of their sources. I have examined specimens from places along a belt of country in Suffolk extending from Lowestoft to Bury St. Edmunds, a distance of more than 50 miles; Lincolnshire material dredged up in deepening the ship-channel to Boston (kindly sent by Mr. W. H. Wheeler, C.E.); Cambridgeshire specimens from Ely Cemetery and