[15] A ha-ha is a boundary to a garden, pleasure-ground, or park of such a nature as not to interrupt the view from the mansion and may not be seen until closely approached. According to a French etymologist, the name is derived from _ha_, an exclamation of surprise, uttered by one suddenly approaching such a boundary. The ha-ha consists of a trench, the inner side of which is perpendicular and faced with a wall; the outer being sloped and turfed. The ha-ha permitted grazing cattle and sheep to appear on the landscape, and at the same time held them at a distance from the mansion. In his diary, George Washington refers, on several occasions, to the ha-has on the grounds at "Mount Vernon." Cf. Fitzpatrick, John, _The Diaries of George Washington_, Vol. II, _passim_. Situated amidst such attractive surroundings, the residences appeared to fine advantage. Their architectural arrangement contributed much to their impressiveness. At the same time it was admirably suited to the peculiar needs of plantation life. The mansion or "great house" was but the central unit, about which, at carefully spaced intervals, stood numerous smaller structures, all subsidiary to it. Spoken of indiscriminately as "offices," these dependent buildings all served some useful purpose or function in the domestic economy. The mansion was usually a substantial two-story, rectangular building of brick, though sometimes it was built of stone or wood. The rather low-pitched roofs were generally shingled with cypress or slate. Since many of the activities of the household were carried on in offices under separate roofs, a central structure approximately seventy-five feet long and forty-two feet wide was usually regarded as commodious. The exteriors of these houses were often characterized by an elegant simplicity achieved through perfection of line and proportion. The severity of a facade might be relieved by a handsome wooden cornice, a pedimented hood over the doorway, a string-course and water table of molded brick, and window and door facings of rubbed brick. Sometimes pilasters of finely molded brick framed the doorways. Not infrequently the principal offices, set in advance or in the rear of the mansion, served as foils to impart greater dignity to it. Sometimes, as at "Blandfield" and "Mount Airy," the major offices were connected with the central building by straight or curved lateral passages. The great house and its dependent structures were generally placed in such a relation as to form one or more rectangular courts.[16] The principal offices were often large and contained a number of rooms.