There are, however, undoubted proofs of considerable age to be found there. Trees have shot up in the midst of the buildings, which measure, it is said, more than nine feet in diameter.[444] A still more striking fact is the accumulation of vegetable mould in one of the courts, to the depth of nine feet above the pavement.[445] This in our latitude would be decisive of a very great antiquity. But in the rich soil of Yucatan, and under the ardent sun of the tropics, vegetation bursts forth with irrepressible exuberance, and generations of plants succeed each other without intermission, leaving an accumulation of deposits that would have perished under a northern winter. Another evidence of their age is afforded by the circumstance that in one of the courts of Uxmal the granite pavement,[446] on which the figures of tortoises were raised in relief, is worn nearly smooth by the feet of the crowds who have passed over it;[447] a curious fact, suggesting inferences both in regard to the age and population of the place. Lastly, we have authority for carrying back the date of many of these ruins to a certain period, since they were found in a deserted, and probably dilapidated, state by the first Spaniards who entered the country. Their notices, indeed, are brief and casual, for the old Conquerors had little respect for works of art;[448] and it is fortunate for these structures that they had ceased to be the living temples of the gods, since no merit of architecture, probably, would have availed to save them from the general doom of the monuments of Mexico. If we find it so difficult to settle the age of these buildings, what can we hope to know of their architects? Little can be gleaned from the rude people by whom they are surrounded. The old Tezcucan chronicler so often quoted by me, the best authority for the traditions of his country, reports that the Toltecs, on the breaking up of their empire,--which he places earlier than most authorities, in the middle of the tenth century,--migrating from Anahuac, spread themselves over Guatemala, Tehuantepec, Campeachy, and the coasts and neighboring isles on both sides of the Isthmus.[449] This assertion, important, considering its source, is confirmed by the fact that several of the nations in that quarter adopted systems of astronomy and chronology, as well as sacerdotal institutions, very similar to the Aztec,[450] which, as we have seen, were also probably derived from the Toltecs, their more polished predecessors in the land.