My life : a record of events and opinions - Wallace-online.org

HOME LIFE AND WORK 267including the causes and effects of the glacial epoch,since these were among the most powerful agents incausing the dispersal of all kinds of organisms, andthus bringing about the actual distribution that nowprevails. This led me to a careful study of Mr.James Croll's remarkable works on the subject of theastronomical causes of glacial and interglacial periods,and I had much correspondence with him on difficultpoints of his theory. While differing on certaindetails, I adopted the main features of his theory,combining with it the effects of changes in heightand extent of land which form an important adjunctto the meteorological agents. To this subject Idevoted two of my longestand most argumentativechapters, introducing many considerations not beforetaken account of, and leading, I still think, to a moresatisfactory explanation of the causes that actuallybrought about the glacial epoch than any which havesince been put forth.Besides this partially new theory of the causes ofglacial epochs, the work contained a fuller statementof the various kinds of evidence proving that thegreat oceanic basins are permanent features of theearth's surface, than had before been given ; also adiscussion of the mode of estimating the durationgeological periods, and some considerationsofleadingto the conclusion that organic change is now lessrapid than the average, and therefore that less timeis required for this change than has hitherto beenthought necessary. I was also, I believe, the first topoint out the great differences between the moreancientcontinental islands and those of more recentorigin, with the interesting conclusions as to geographicalchanges afforded by both ;while the mostimportant novelty is the theory by which I explained