I endeavoured to trace the plan of the ancient inclosure, which contained a group of the greatest archæological importance, but so many of the mounds had been levelled, that it was difficult to form definite conclusions with regard to its shape or extent. It seems to have been an irregular parallelogram, about fifteen hundred yards in length, having at each end a large earthwork or mound, with a wide and well levelled platform on the top. In the centre, there were two conical mounds, which must have been raised in that position for some important purpose. They were each about forty feet high, and appeared to have been so placed as to dominate the mounds forming the sides of the inclosure. The men farming the adjacent plains, stated that there had been a large number of small burial mounds on their lands, most of which had been destroyed. They had found in them quantities of bones and skulls, but no ornaments or stone weapons. When ploughing the ground, they had seen below the surface, fragments of rude pottery and many flint arrow heads. A large and highly polished stone spear head was discovered near the settlement and given by the finder to the young American lady who was then acting as teacher at the school house on the mound. It was a hard kind of flinty chert, and was a singularly fine specimen of Indian workmanship.[31] When I had completed the measurement of the spaces inclosed by the mounds on the plain, I returned to the great mound in order to examine it, and my previous conjecture that it was a natural formation remained unchanged. It was, however, impossible to form a decided opinion upon the subject, for it required a properly executed scientific investigation to be made, before the problem of the construction could be determined. If it should be proved to be artificial, its position and shape as a high platform earthwork, would support a theory, that it was raised by the same race that built the greater temple platform of Cholula, in Mexico. After quitting the Cahokia mounds and traversing several miles of the plains, where for centuries many generations of Indians had encamped, I returned to St. Louis and embarked on board the Muscatine, a steamer about to proceed to the highest part of the navigable waters of the Mississippi. Sixteen miles above St. Louis we passed the mouth of the Missouri, and observed how its waters, thickly charged with earth, entirely changed the character of the river into which it flowed. Above the confluence, the Mississippi is a clear, tranquil stream, but after receiving the Missouri it becomes muddy, rushing, and turbulent.[32] [Illustration: INDIAN MOUNDS, CAHOKIA.]