A still more remarkable group was brought under the notice of the Society in 1816 by Professor Stuart of Aberdeen. They are spread over a space of a mile or two in diameter on what was then a dry moor in the parishes of Auchindoir and Kildrummy, in Aberdeenshire. These excavated houses, he says, are most frequently discovered by the plough striking against some of the large stones which form the roof. The only opening to them appears to have been between two large stones placed in a sloping direction at one end, and about 18 inches asunder. Through this narrow opening one must slide down to the depth of 5 or 6 feet, when he comes to a vault generally about 6 feet high, upwards of 30 feet long, and 8 or 9 feet wide. The floor is smooth, as if of clay, and the sides are built of rude undressed stones without cement. The walls bend inwards to form a rude arch, and the roof is covered with large stones 5 or 6 feet long, some of them being over a ton in weight. The whole structure is beneath the level of the ground and quite invisible, but many of them were detected by the existence close to them of a square space about 10 to 15 paces each way dug a foot or two deep with the earth thrown outwards. These he conjectures to have been the sites of the summer huts of the people, who retreated to these underground places in winter, and stored their provisions and concealed their valuables in them all the year round. But he adds that no article of furniture, and no utensils or instruments either of stone or metal have been found in them so far as can be learned, but only a quantity of wood-ashes and charcoal, chiefly at the farther end, where there sometimes appears a small aperture at the top as an outlet for the smoke. The whole number discovered in this locality he estimates at between forty and fifty. They are found, he says, in other localities, but so great a number collected in one place has probably never before occurred. The number is certainly very large, and may probably be over estimated, but it would not be difficult to find in other parts of Scotland, and specially in Aberdeenshire, a series of groups of similar structures which, though not so numerous or so closely aggregated, are so distributed over wide districts as to show that the custom of constructing these underground edifices was general and prevalent. Wherever they occur they present the same individuality of character and the same strongly marked typical features. Their range in area extends from Berwickshire to Shetland. They occur in greater or less abundance in most of the counties bordering on the east coast. A few doubtful examples only are recorded in those bordering on the west coast. But it is only of late years that the importance of securing a permanent and exhaustive record of such casual discoveries has begun to be recognised, and in this direction of defining the areas of the respective types of structural antiquities, we are still groping in darkness on the threshold of a great investigation.