I Have been very much interested in reading Mr. Russell's two communications published in the Geological Magazine for August and September last. The analogy which he draws between the history of the Dead Sea valley and that of some of the lake valleys in the western part of North America is instructive as showing how similar physical features can be accounted for on similar principles of interpretation over all parts of the world. Mr. Eussell very properly draws attention to the paper by his colleague Mr. G. K. Gilbert on “The Topographical Features of Lake Shores,” in which principles of interpretation of physical phenomena are laid down applicable to lakes both of America and the Jordan-Arabah valley. With some of Mr. Russell's inferences regarding special epochs in the history of this valley I am very much disposed to agree; more particularly in reference to the mode of formation of the Salt Mountain, Jebel Usdum; or rather, of the salt-rock which forms the lower part of its mass. If this interpretation be correct, it removes the difficulty of understanding why the rock-salt is confined to one small corner of the lake, which, at the time the salt was in course of formation, was vastly more extensive than at present.