Those of the upper stories, which rise from them, and form the habitable part of the house above, are much slighter than the lower ones, and the joists and wooden-work about the roof are adapted for security against such accidents, by their being fastened with bolts on either side of the masonry, thus enabling it to give a little play to the motion of the shock, without being displaced by it, and coming down, as thick and heavy walls would most certainly do.