ABSTRACT
Whereas Lyell’s marine dissection theory was still remarkably unimpaired by criticisms in the mid-nineteenth century, his ideas on iceberg deposition were showing signs of being undermined by the glacial theory. It is true that the widespread occurrence of glacial deposits or drift tended to support Lyell’s contention of a recent marine submergence but the distribution of large erratic boulders was often less happily explained by marine or iceberg agencies. Because of Agassiz’s writings and lectures, the action of mountain glaciers in grinding their way slowly down valleys and heaping up morainic mounds at their snouts, was well understood, but few geologists were also willing to accept the necessary extension of the glacial theory-that vast ice-sheets had once spread over the lowlands of much of Europe and North America. The solution of the problem was hindered by the fact that, as Agassiz had pointed out, over vast areas, the marshy terrains, gravel deposits and winding ridges of poorly stratified material all bore the signs of having had some connexion with water. Much glaciated topography was in fact fluvio-glacial or the work of ice and of melt-water. This and Lyell’s omnipotence largely explain why marine explanations were still so widely followed.
