The Keep is seventy feet square and a hundred feet high, built of the native Kentish ragstone and Caen stone; and the adamantine mortar or cement used in its construction was made with sand, evidently procured at the seaside some distance from Rochester, for it contains remains of cardium, pecten, solen, and other marine shells, which would not be found in river sand. Mr. Roach Smith suggested that probably the sand may have been procured from "Cockle-shell Hard," near Sheerness. He called our attention to the fact that in Norman mortar sand is predominant, and in Roman mortar lime or chalk. [Illustration: Rochester Castle] The roof and the chambers are gone,--the Keep remains as a mere shell,--and where bishops, kings, and barons came and went, flocks of the common domestic pigeon, in countless numbers, fly about and make their home and multiply. One almost regrets the freedom which these graceful birds possess, although to grudge freedom to a pigeon is like grudging sunshine to a flower. But though the damage to the walls is really trifling, as they will stand for centuries to come, still the litter and mess which the birds naturally make is considerable and unsightly, and decidedly out of keeping in such a magnificent ruin. The pigeons exhibit what takes place when a species becomes dominant to the exclusion of other species, as witness the pest of the rabbits in New Zealand. With profound respect to his Worship the Mayor and the Corporation of Rochester, to whom the Castle and grounds now belong, the writer of these lines, as a naturalist, ventures to suggest that the Castle should be left to the jackdaws, its natural and doubtless its original tenants, which, although of higher organization, have been driven out by superior numbers in the "struggle for existence," and for whom it is a much more appropriate habitat in keeping with all traditions; and further, that the said pigeons be forthwith made into pies for the use and behoof of the deserving poor of the ancient city of Rochester. Mention has been made of the fact that the Castle and grounds are the property of the Corporation of Rochester. They were acquired by purchase in 1883 from the Earl of Jersey for L8,000, and the occasion was celebrated by great civic rejoicings.[6] The Corporation are not only to be congratulated on the wisdom of their purchase ("a thing of beauty is a joy for ever"), but also on the excellent manner in which the grounds are maintained--pigeons excepted. The gardens, with closely-cut lawns, abound with euonymus, laurustinus, bay, and other evergreens, together with many choice flowers. The single red, or Deptford pink (_Dianthus Armeria_), grows wild on the walls of the Castle. There is a tasteful statuette of her Majesty, under a Gothic canopy, near the entrance, which records her Jubilee in 1887. The inscriptions on three of the four corners are appropriately chosen from Lord Tennyson's _Carmen Saeculare_:-- To commemorate the