Amongst those [works] of the tenth century, of which fragments are now extant, is a system of mineralogy by Avicenna, a physician in whose arrangement there is considerable merit. In the same century also, Omar, surnamed 'El Aalem,' or 'the Learned,' wrote a work on 'the Retreat of the Sea.' It appears that on comparing the charts of his own time with those made by the Indian and Persian astronomers two thousand years before, he had satisfied himself that important changes had taken place since the times of history in the form of the coasts of Asia, and that the extension of the sea had been greater at some former periods. He was confirmed in this opinion by the numerous salt springs and marshes in the interior of Asia,-a phenomenon from which Pallas, in more recent times, has drawn the same inference.