The remarkable specimen which forms the subject of this communication was presented to me by Mr. Reid Moir, who had extracted it with his own hands from the base of the Red Crag exposed in Messrs. Bolton & Laughlin's brick field, near Ipswich.

It is a fragment of a nodule of chalk flint, irregularly rhombic in outline, with nearly flat base and a rounded upper surface which slopes away on each side from a medium line (the shorter diameter) joining the two obtuse angles of the rhomb.

The upper rounded side formed part of the original surface of the nodule and retains the whitish weathered crust, 8 mm. or more in thickness, which was formed while the nodule lay embedded in the chalk. The exterior of this crust has since been traversed by solutions which have deposited in its pores some silica and ferric hydrate, thus forming a brown superficial layer which is now too hard to be scratched with a knife.