The largest ruins of this type invariably lie near the main lines of drainage. They consist of villages with houses of several storeys. But digging down beneath these ruins we find (_c_) traces of an older occupation, and ruins of a primitive type are also found on the plateaus remote from any except small valleys. “They are usually small, and are greatly ruined, and seem to belong to a time long anterior to the main large ruins.” Huntington terms this type the Hohokam; unfortunately this and the Pajaritan occupations cannot be accurately dated, but it is reasonable to connect them with the rainfall maxima shown by the trees, about the time of Christ, and in A.D. 1000 to A.D. 1300. A similar succession has been found in the neighbourhood of Mexico City. The earliest trace of occupation is a crude “mountain pottery,” in ordinary river sand and gravel. These deposits are succeeded by finer sand with better pottery known as the “San Juan” type, above which comes a culture layer with the remains of houses. This is covered by a bed of “tepetate,” a white calcareous deposit frequently found in dry regions where much water evaporates. The gravels suggest the occasional heavy rains of arid countries. The San Juan pottery extends throughout the “tepetate,” which probably corresponds to the dry period of A.D. 400-1000 in California. Historical records in Mexico date back to the coming of the Aztecs in A.D. 1325. They show that in 1325 and again in 1446 the level of the lake of Mexico was high, but towards the end of the fifteenth century the water was much lower. In 1520 it was high again; in 1600 it was low, but high from 1629 to 1634. From 1675 to 1755 was a long dry period. On the whole the climate from 300 to 600 years ago seems to have been moister than that of to-day. Still further south in the Peninsula of Yucatan recent explorations have yielded results of extreme interest. Yucatan lies within the tropical rain-belt, and is covered by almost impenetrable forests. The climate is enervating and unhealthy, and the present inhabitants are greatly lacking in vigour. In the forest, however, have been found the ruins of ninety-two towns, some of them of great size, and all remarkable for the beauty as well as the solidity of their architecture.