This enclosure is situate on the highest point of land in the vicinity of Auburn, and is in the form of an ellipse and measures in diameter, from east to west, (from the outside of the base of the embankment) four hundred and sixteen feet, and from north to south, three hundred and ten feet; the circumference, twelve hundred feet; present height of the highest part of the embankment on the west side from the bottom of the ditch, four feet; the thickness at the base, fourteen feet; from the centre of the enclosure the ground has a gentle slope to the north, east and west, and is nearly level towards the south. The openings on the south, one of sixty and the other of seventy-eight feet, are directly opposite or against deep ravines separated by a narrow steep ridge, access through which would be difficult, being on an angle of nearly forty-five degrees. The opening on the north measures one hundred and sixty-six feet, opposite to which the ground continues to slope to the north for the distance of seventy feet, from which point the descent is very abrupt. The opening on the east measures sixty-six feet, opposite to which the ground continues on a gentle descent to the east for several hundred feet. The opening on the southwest measures fifty feet, and is opposite to a ridge gently descending to the southwest. There are no less than ten deep ravines and as many steep ridges surrounding and leading to this ancient fortification. McAuley, in his history of the State of New-York, Vol. 2d, pages 111 and 112, gives a minute and interesting description of this fortification, which, however, contains some inaccuracies; and also of another fortification situate in the northeast part of Auburn. The large chesnut stump described by him as standing in the moat on the west side of the enclosure, is still to be seen; there are still to be seen the remains of two large oak stumps, which seem to have escaped his notice, situate on the southeast side of the enclosure, one of them on the top of the embankment, and the other in the ditch some twelve feet distant. There are scarcely any traces remaining of the fortification described by McAuley as being in the north east part of Auburn, from the fact that the ground upon which it stood has been under cultivation for many years. JAMES H. BOSTWICK, _Surveyor_. _October 16_, 1845. (F.) Letter from Frederick Follet to Henry R. Schoolcraft. _Batavia, Oct. 25_, 1845. DEAR SIR—My private and public duties together prevented my making a visit to “Fort Hill,” until the 22d inst. and I proceed to give you my ideas of that formation.