Such a chisel lay on the floor of the hut, and by comparing it with the marks of the tool used in forming the mortises, they were found "to correspond exactly, even to the slight curved exterior of the chisel; but the logs had been hewn by a larger instrument, in the shape of an axe. On the floor of the dwelling lay a slab of freestone, 3 feet long and 14 inches thick, in the centre of which was a small pit three quarters of an inch deep, which had been chiselled out. This is presumed to have been used for holding nuts to be cracked by means of one of the round shingle stones, also found there, which had served as a hammer. Some entire hazel-nuts and a great quantity of broken shells were strewed about the floor." The foundations of the house were made of fine sand, such as is found with shingle on the seashore about 2 miles distant. Below the layer of sand the bog or peat was ascertained, on probing it with an instrument, to be at least 15 feet thick. Although the interior of the building when discovered was full of "bog" or peaty matter, it seems when inhabited to have been surrounded by growing trees, some of the trunks and roots of which are still preserved in their natural position. The depth of overlying peat affords no safe criterion for calculating the age of the cabin or village, for I have shown in the "Principles of Geology" that both in England and Ireland, within historical times, bogs have burst and sent forth great volumes of black mud, which has been known to creep over the country at a slow pace, flowing somewhat at the rate of ordinary lava-currents, and sometimes overwhelming woods and cottages, and leaving a deposit upon them of bog-earth 15 feet thick. None of these Irish lake-dwellings were built, like those of Helvetia, on platforms supported by piles deeply driven into the mud. "The Crannoge system of Ireland seems," says Mr. Wylie, "well nigh without a parallel in Swiss waters." CHAPTER 3. -- FOSSIL HUMAN REMAINS AND WORKS OF ART OF THE RECENT PERIOD--CONTINUED. Delta and Alluvial Plain of the Nile. Burnt Bricks in Egypt before the Roman Era. Borings in 1851-54. Ancient Mounds of the Valley of the Ohio. Their Antiquity. Sepulchral Mound at Santos in Brazil. Delta of the Mississippi. Ancient Human Remains in Coral Reefs of Florida. Changes in Physical Geography in the Human Period. Buried Canoes in Marine Strata near Glasgow. Upheaval since the Roman Occupation of the Shores of the Firth of Forth. Fossil Whales near Stirling. Upraised Marine Strata of Sweden on Shores of the Baltic and the Ocean. Attempts to compute their Age. DELTA AND ALLUVIAL PLAIN OF THE NILE.