Returning to the confluence of the Missouri with the Mississippi, the point at which we left the western boundary of the Mound-builder country in order to treat the characteristics of its central region, we find mounds, as we previously stated, in great numbers in the neighborhood of St. Louis. In the valley of the St. Francis River, mounds that have been explored have yielded many rich relics, artistic water vessels, vases and statuettes. In Green County, Missouri, N. Lat. 37° 20´ and 16° Long, west of Washington City, is a very remarkable truncated conical mound which has only been externally surveyed. This mound is 60 feet high, 350 feet in diameter at the base, and 130 feet in diameter on the top. It is surrounded by a trench (except about twenty feet at the north) about two hundred feet wide and four feet deep. On the north the excavation is seven or eight feet deep.[57] These trenches served a double purpose—that of furnishing material for the construction of the mound, and when completed, of providing an impassable moat filled with water, that neither enemies nor the rabble might approach the sacred mount.[58] In Phillips County, Prof. Cox discovered an ancient fortification near Helena, built like a part of the Seltzertown mound, of sun-dried bricks; stems and leaves of the cane were used instead of straw in making the bricks.[59] Professor Swallow, in company with a number of scientific gentlemen, opened a large mound in Lewis’ Prairie, west of New Madrid, Missouri (in December, 1856), in which he found a great collection of earthen dishes and vases. The mound was elliptical in form, measuring 900 feet in periphery at the base, 570 feet at the top and twenty feet in height. The remarkable feature of the mound was that it contained a room formed of poles, lathed with split cane and plastered with clay both inside and out, forming a solid mass. “Over this room was built the earthwork of the mound, so that when it was completed the room was in its centre. The earthwork was then coated with the plaster, and over all nature formed a soil. This mud plastering was left rough on the outside of the room, but smooth on the inside, which was painted with red ochre.”[60] Some of the plastering was burned as red and hard as brick, while other parts were only sun-dried. Professor Swallow believes the mounds of the region to be very ancient. On mounds and neighboring embankments a sycamore tree twenty-eight feet in circumference, three feet above the ground, a black-walnut twenty-six feet in circumference, a white ash twelve feet and a chestnut oak eleven feet in circumference were observed. In addition to these evidences of age, the Professor states that six feet of stratified sands and clays have formed around the mounds since they were deserted. (See Eighth _Annual Report of Peabody Museum_, pp. 16 _et seq._ Cambridge, 1875.)