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Rh I had further sustained by personal examination of the rocks of Permian age in various other countries of Europe.

It was, indeed, evident that M. Marcou's proposed union of the so-called Dyas and Trias in one natural group could not for a moment be maintained, since there is no conclusion on which geologists and palæontologists are more agreed, than that the series composed of Roth-liegende, Kupfer-Schiefer, Zechstein, etc., forms the uppermost Palæozoic group, and is entirely distinct in all its fossils, animal and vegetable, from the overlying Trias, which forms the true base of the Mesozoic or Secondary rocks.

Owing to such a manifest confusion respecting the true palæontological value of the proposed "Dyas," we should probably never have heard more of the word, had not my distinguished friend, Dr. Geinitz, of Dresden, recently issued the first volume of his valuable palæontological work, entitled 'Dyas, oder die Zechstein-Formation und das Rothliegende.' In borrowing the terra "Dyas" from Marcou, Dr. Geinitz shows, however, that that author had been entirely mistaken in grouping the deposits so named with the Trias or the Lower Secondary rocks, and necessarily agrees with me in considering the group to be of Palæozoic age.

As there is no one of my younger contemporaries for whom I have a greater respect as a man of science, or more regard as a friend, than Dr. Geinitz, it is painful, in vindicating the propriety and usefulness of the word "Permian," to be under the necessity of pointing out the misuse and inapplicability of the word "Dyas."

The term "Permian" was proposed twenty years ago for the adoption of geologists, without any reference whatever to the lithological or mineral divisions of the group; for I well knew that a certain order of mineral succession of this group prevailed in one tract, which could not be followed out in another. After surveys, during the summers of 1840 and 1841, of extensive regions in Russia in Europe, in which fossil shells of the age of the Zechstein of Germany, and the Magnesian Limestone of England, were found to occur in several courses of limestone, interpolated in one great series of red sandstones, marls, pebble-beds, copper-ores, gypsum, etc., and seeing that these varied strata occupied an infinitely larger superficial area than their equivalents in Germany and other parts of Europe, I suggested to my associates, when we were at Moscow in October, 1851, that we should employ the term "Permian," as derived from the vast government of that name, over which and several adjacent governments we had traced these deposits.

In a letter addressed to the late venerable Dr. Fischer von Waldheim, then the leading naturalist of Moscow, I therefore proposed the term "Permian," to represent by one unambiguous geographical