In the first decades of the last century, Charpentier and others, examining the large boulders of foreign rocks in major valleys in the Alps, were eventually persuaded that the local peasants were right. Glaciers, then small and restricted to the upper parts of the valleys, had once been far more extensive and carried with them these boulders from source areas farther up the valleys (Flint, 1971). Once convinced that only ice in the form of large glaciers (rather than some preternatural floods) could move such large debris over wide areas, it was inevitable that other large boulders of foreign rocks scattered elsewhere throughout northern Europe would be interpreted as having been transported the same way, only in this case by continental size ice masses. Thus, the Glacial Theory was born.
No isolated musing, however informed, could have arrived at such a conclusion. If the boulders had been next to a large river, it is possible to envision a totally different conclusion arising from these early observations, and establishment of the Glacial Theory delayed for some time. Unfortunately, the historical development of ideas of sea level variations during the late Holocene (ca. 5 BP-present) cannot point to a similar single instance where long, if not widely, recognized physical evidence finally connected with an enlightened reception. However, the type and quality of the evidence have been equally important in how concepts have evolved, and why controversies on the most basic of questions concerning past sea level change remain current.
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