a1 University of Bonn-on-the-Rhine.
[The following communication, although addressed to the Editor in the form of a letter, is of such importance that we need make no apology for treating it as an Original Article, feeling sure that our readers will be as much interested as ourselves in the observations of so eminent a geologist, who has spent many years in actual study of these vast deposits, as to the origin of which he is consequently able to speak with such profound knowledge and mature judgment. —Edit. Geol. Mag.]