and a third edition would require still further changes. I may recall the well-known fact that in geological treatises, published not many years ago, mammals were always spoken of as having abruptly come in at the commencement of the tertiary series. And now one of the richest known accumulations of fossil mammals belongs to the middle of the secondary series; and true mammals have been discovered in the new red sandstone at nearly the commencement of this great series.
eta hirugarren argitaraldiak are aldaketa gehiago beharko lituzke. Ongi ezaguna den egitate bat gogorarazi behar dut, alegia, duela urte gutxi argitaraturiko geologiako tratatuetan, ugaztunei buruz serie tertziarioaren hasieran bat-batean agerturikotzat hitz egiten zela. Eta egun ezagutzen den ugaztun fosilen aztarnategirik aberatsenetako bat serie sekundarioaren erdialdekoa da; eta benetako ugaztunak aurkitu dira serie handi honen ia hasierako egungo harearri gorrian.