With reference to the general or periodical lowering of the temperature of the globe, I have never thought it necessary, on account of the elephant of the Lena, to admit that sudden frost of which Cuvier used to speak. What I have seen in Siberia, and what has been observed in Captain Beechey's expedition on the northwest coast of America, simply proves that there exists a layer of frozen drift, in the fissures of which (even now) the muscular flesh of any animal which should accidentally fall into them would be preserved intact. It is a slight local phenomenon. To me, the ensemble of geological phenomena seems to prove, not the prevalence of this glacial surface on which you would carry along your boulders, but a very high temperature spreading almost to the poles, a temperature favorable to organizations resembling those now living in the tropics. Your ice frightens me, and gladly as I would welcome you here, my dear friend, I think, perhaps, for the sake of your health, and also that you may not see this country, always so hideous, under a sheet of snow and ice (in February), you would do better to come two months later, with the first verdure. This is suggested by a letter received yesterday by M. d'O--, which alarmed me a little, because the state of your eyes obliged you to write by another hand. Pray do not think of traveling before you are quite well. I close this letter, feeling sure that it does not contain a line which is not an expression of friendship and of the high esteem I bear you. The magnificence of your last numbers, eight and nine, cannot be told. How admirably executed are your Macropoma, the Ophiopris procerus, Mantell's great beast, the minute details of the Dercetis, Psammodus,. . .the skeletons. . . There is nothing like it in all that we possess upon vertebrates. I have also begun to study your text, so rich in well arranged facts; the monograph of the Lepidostei, the passage upon the bony rays, and, dear Agassiz, I could hardly believe my eyes, sixty-five continuous pages of the third volume, without interruption! You will spoil the public. But, my good friend, you have already information upon a thousand species; "claudite jam rivos!" You say your work can go on if you have two hundred subscribers; but if you continue to support two traveling draughtsmen, I predict, as a practical man, that it cannot go on. You cannot even publish what you have gathered in the last five years. Consider that in attempting to give a review of all the fossil fishes which now exist in collections, you pursue a phantom which ever flies before you. Such a work would not be finished in less than fifteen years, and besides, this NOW is an uncertain element. Cannot you conquer yourself so far as to finish what you have in your possession at present? Recall your artists. With the reputation you enjoy in Europe, whatever might essentially change your opinion on certain organisms would willingly be sent to you. If you continue to keep