responsible for the formation of till. Dobson, however, was not a highly regarded scientific figure; consequently, his ideas received little notice, and his article slipped into obscurity, unread.

Eventually, similar ideas struck the minds of other geologists. Charles Lyell, an Englishman and perhaps the most respected geologist of the 19th century, proposed that most of the unusual aspects of sediments covering the bedrock were due to icebergs floating in the torrent of Noah's flood. Whaling men, who sailed far into cold Arctic and Antarctic waters, had long noticed that icebergs were often very dirty, sometimes black with grit and rocks ground off Antarctica and Greenland and encased in the ice. Lyell reasoned that as these drifting icebergs melted, the sediment within would have been dumped in a disordered mess practically anywhere - including hillsides high above the reach of rivers. Hence, any sediment clearly not deposited by an existing river came to be called "drift" named for the drifting icebergs that were thought to have left it. He also pointed out that since eight-ninths of an iceberg's bulk is below water line, icebergs could have scraped and bumped the bedrock surface beneath as they floated with the currents of Noah's flood. Thus, the troublesome scratches and striations that scored bedrock were the result of the scraping action of rocks frozen into the great keels of drifting icebergs. The iceberg theory of drift and striations was really a very clever idea and quickly attracted many ardent advocates.

The iceberg theory was a step closer to the present explanation for the origin of drift, striations, and other associated features such as drumlins. The modern explanation was soon forthcoming. In 1846, Swiss naturalist Louis Agassiz arrived in the United States full of ideas that had been stirring up a hotbed of controversy in Europe. What Agassiz had proposed for Europe - and soon proposed for North America as well - was that the northern portions of these continents had once been covered by massive glaciers. The action of glaciers could account for most of the puzzling surface features of northern regions. Agassiz envisioned massive ice sheets on each continent that advanced southward from the far north. As the ice bulldozed its way across the land, it stripped off the loose soil and ground the bedrock smooth.

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