Stratification of Remains.
Atzcapotzalco was once an important center of the Tepanecan tribe situated on the shores of lake Texcoco. It was an early rival of Tenochtitlan, the Aztecan capital, and was conquered and partly destroyed in 1439. The principal modern industry of Atzcapotzalco is brick-making, and several mounds and much of the surface of the plain have been removed for this purpose. In the mounds are found many pottery objects of the late Toltecan period, while on the surface of the ground are encountered fragments of the typical Aztecan pottery in use when the Spaniards arrived.
Fig. 10. Atzcapotzalco Destroyed. The temple burns at the Place of the Ant.
The stratification of the plain varies in different places so far as the thickness of the different strata is concerned, but the order is always the same. At one locality it is as shown in [Fig. 11]. First comes a layer of fine soil of volcanic ash origin, probably deposited by the wind. This is five or six feet in thickness, yellowish at the top, and much darker towards the bottom, with streaks and discolorations. The Aztecan pottery is found close to the surface, while Toltecan pottery occurs in the middle and lower sections. Underneath the soil layers lies a thick stratum of water-bearing gravel mixed with sand. This gravel stratum is possibly the old bed of a stream that formerly entered Lake Texcoco near this point. In some places it is fifteen or eighteen feet in thickness. Scattered throughout the gravel are heavy, waterworn fragments of pots as well as more or less complete figurines of the archaic type.
Fig. 11. Diagram of Culture Strata at Atzcapotzalco.
Temple mounds of Toltecan period. Surface finds of Aztecan period. Remains of Toltecan period. Deep stratum of water-bearing gravels containing remains of archaic period. Bed rock of hard clay.
At other sites, such as Colhuacan, the Toltecan layer is of greater thickness and the archaic layer of lesser thickness. The remains extend below the present level of the water and may indicate that considerable changes have taken place in the level of the lake. But we must remember that many of the ancient settlements were built over the water and that land was made in ancient times, as it is today in the gardens of Xochimilco, by deepening canals. Archaic remains are also common on the denuded tops of hills which may once have been covered by soil.
A stratification of archæological remains has recently been determined in Salvador.