the different orders of the same class, or in the various genera of the same order. If, on the other hand, the development of the palæozoic creation be considered relatively to its horizontal extent, or geographically in relation to space, it will be seen, 1st, that the species which are found in a great number of localities, and in very distant countries, are almost always those which have lived during the formation of several successive systems; 2nd, that the species which belong to a single system are rarely observed at great distances, and that they then constitute local faunæ, peculiar to certain countries; whence it results that the species really characteristic of a system of beds are so much the less numerous as the system is studied upon a vaster scale." It must be remembered that these most important generalizations were communicated to this Society in the year 1841, and though the able authors of the memoir express their satisfaction at finding their conclusions in accordance with those independently arrived at by Prof. Phillips, I am not sure that either their substance, or their origin, is even now quite so familiar to palæontologists as it ought to be.
From 1842 to 1847, M. d'Archiac was occupied with the investigation of the Cretaceous and Tertiary deposits of France and Belgium, and published several valuable works, among which I may mention the 'Description Géologique du Département de l'Aisne' (1843), and the 'Description des fossiles des couches nummulitiques des environs de Bayonne' (1846 and 1850). The line of inquiry opened up by the last-mentioned works could not fail to be attractive to so philosophical a geologist and biologist; but few men are blessed with the prodigious industry which enabled D'Archiac to produce, in seven years, not only these memoirs, but the major part of the great monograph on the Nummulitic formation of India, which was published in 1853; while at the same time he was occupied with such a work as the 'Histoire des progrés de la Géologie de 1834 à 1845,' five volumes of which appeared between 1847 and 1853. I have had the curiosity to put together the total number of pages of these five volumes, and I find that, for this work only, D'Archiac must have written, on the average, the matter which fills 600 closely printed octavo pages every year for six years. And when we consider that this matter consists of a fair and faithful critical digest of innumerable books and memoirs, all which must needs have been read, and that it contains a great amount of original thought, one's respect for its author's power of work rises almost into awe.
The eighth volume of this extremely valuable work was published in 1860, and it is profoundly to be regretted that it remains incomplete. The author's plan is to deal with the history of each formation in successive order, from the youngest to the oldest, starting with the year 1834, and carrying his history, in the early volume, as far as 1845, in the later volumes to a more recent date. The last volume deals with the history of Triassic geology from 1834 to 1859.
In 1857 M. d'Archiac was elected a member of the Academy of Sciences, in the place of M. Constant Prévost; and, on the death of
