Charles Darwin visited the glen in June 1838 and, drawing on his recent findings in South America during the "Beagle" expedition concluded that the shorelines were raised beaches of marine origin. His paper on the subject was published in 1839 in the "Philosophical Transactions of the Royal Society". This was contradicted in 1840 by Louis Agassiz's Glacial theory which postulated that the Glen Roy shorelines had been cut by freeze-thaw processes of loch ice during the maximum extent of glacial ice in the climatic reversal known as the Younger Dryas / Greenland Stadial, or locally the Loch Lomond Readvance. Darwin defended his paper over many years.