Hugh Miller has an interesting observation concerning the actual date of geologic phenomena in North America, compared with that of their counterparts in the Old World. He says, "The much greater remoteness of the mastodontic period in Europe than in America is a circumstance worthy of notice, as it is one of many facts that seem to indicate a general transposition of at least the later geologic ages on the opposite sides of the Atlantic. Groups of corresponding character on the eastern and western shores of this great ocean were not contemporaneous in time. It has been repeatedly remarked that the existing plants and trees of the United States, with not a few of its fishes and reptiles, bear in their forms and constructions the marks of a much greater antiquity than those of Europe. The geologist who set himself to discover similar types on the eastern side of the Atlantic, would have to seek for them among the deposits of the later tertiaries. North America seems to be still passing through its later tertiary ages; and it appears to be a consequence of this curious transposition, that while in Europe the mastodontic period is removed by two great geologic eras, from the present time, it is removed from it in America by only one."[11] Professor Agassiz has expressed opinions of the same character, adducing the present existence in America of several forms of animals, which are known in this hemisphere only in a fossil state.[12] I cannot refrain from adding the following combination of fact and speculation, from the pen of an accomplished traveller in Mexico. It opens up a new train of ideas:-- "Some time before our visit, a number of workmen were employed on the neighbouring estate of Chapingo, to excavate a canal over that part of the plain from which the waters have gradually retired during the last three centuries. At four feet below the surface, they reached an ancient causeway, of the existence of which there was of course not the most remote suspicion. The cedar piles, by which the sides were supported, were still sound at heart. Three feet below the edge of this ancient work, in what may have been the very ditch, they struck upon the entire skeleton of a Mastodon, embedded in the blue clay. Many of the most valuable bones were lost by the careless manner in which they were extricated; others were ground to powder on their conveyance to the capital, but sufficient remained to prove that the animal had been of great size. My informant measured the diameter [_qu._ circumference?] of the tusk, and found it to be eighteen inches.