Grotto or shell house in the grounds of Thames Eyot

PLAN AND MATERIALS: The grotto or shell house is square on plan internally, approximately 2.3 m x 2.3 m and 2 m high, with a brick built vault supported on low brick walls. The shell house is concealed beneath a turfed mound of earth in the manner and scale of an ice house, such that it has been suggested that it may have been the remodelling of an ice house or the ground level of a raised garden building such as the structure depicted on Tillemans view. It opens from the north-western end of the loggia. The wide, arched opening, in dark red, purple and grey brick appears to coincide with the first phase of decoration of the vault and side and rear walls as a grotto, when it was enclosed on three sides and open to the south-east. At a later date the arched opening was partly in-filled in red-brown brick forming a narrower entrance which appears externally to be asymmetrically placed, but from the inside is placed roughly central, creating an enclosed chamber. The arch is crudely jointed suggesting that it may have been rendered or decorated or that it had been a modest garden structure. The exposed, exterior, southern boundary wall flanking the entrance arch, where the rear of the loggia is not clad in stone, is also clad in knapped flint.

INTERIOR: The interior appears to have a solid, earth floor, which has accumulated within it, and added later C20 brick stub walls. The inner lining of the shell house is decorated in a pattern of shells, pebbles, coloured stone, and slag and fragments of glass and pottery, which survive on the vault where two thirds of the decoration is intact and on the vertical walls. The centre of the roof is designed in a regular pattern of spokes made up of small winkles, which radiate from a central hub, and concentric rings of iron-coloured pebbles and flint, and pink, red and blue slag, on a base infilled in larger scallops. The curved vault is lined in a grid of panels in the manner of a coffered ceiling, which follow the profile of the shell house, marked out in vertical ribs of small scallops. Rectangular sections have large a scallop at the centre, surrounded by smaller scallops, pebbles and blue slag. The rear of the shell house is distinguished by a brown flint and pebble arch with a prominent keystone. Below it, the rear face of the vault is enhanced with fragments of pottery and glass. A deep band of flint and slag marks the distinction between the vault and the walls on three sides. The side walls are decorated in a random scatter of flint and pebbles and slag and circles and lozenges of buff and brown pebbles. The inner face of the entrance wall is lined in bands of blue slag and flint. The springing of the reduced entrance arch is lined in panels of small scallops and blue slag, the southern jamb of the arch is lined in flint which extends to the outer surface of the wall.