“1. _Tufa_: A substance freely used by the Romans wherever obtainable, and always considered to mark their work as certainly as if dated and recorded in some historical document. Quantities of it may still be dug in parts of the valley of Dover, by the river. It was squared up, and used in tolerably regular courses of blocks; those inside showing a fair and even facing, hard, and little friable either by age or weather. “2. _The concrete, or mortar_: This is of two kinds, found at two levels of the lower mass of the tower. A small portion has been laid in a pale, tawny-coloured mortar, mixed in the proportion of four parts of sharp grit to one of lime. The greater part, however, has been carried up with the pink or salmon-coloured mortar, peculiar to Roman work, and mixed in the proportion of one part of lime to four of more or less finely-pounded Roman brick. It is nothing like so hard as the concrete found (for instance) lining the Roman baths discovered under the west end of the nave of St. Mary’s parish-church; but it is too peculiar a material not to be recognized wherever it appears, identifying its Roman make. “3. _The red tile-brick_: This, again, is always esteemed a very distinctive element in materials of Roman building; but it requires some attention to distinguish justly between the genuine Roman production and subsequent imitations of the same thing. Without digressing into the habits of a Roman brick-yard, it may suffice just to refer to what is described in well-known ancient authorities, as the careful process observed in the making of Roman tile-brick. A very pure and smooth clay was selected, and so treated as to expel as much as possible all gritty and non-homogeneous ingredients. Reduced to something like the fineness and consistency of dough, it underwent a treatment not very different from that of the dough itself; being laboriously wrought and tempered by hand or otherwise, like bread being kneaded in its trough; it was then shaped off in flat blocks of the various sizes employed. The sizes vary considerably as found in different places; but those commonly seen along the Kentish coast in bonding-courses, or the construction of arches, are something over a foot square, by about two inches in thickness. They are generally more or less deeply scored on the under face, either in a rude pattern, or simply with straight or wavy lines, making their hold on hard mortar very tenacious; though these are not unfailing marks of Roman brick.”