relation vague. Prof. Zittell, of Munich, did not think the method of correlation by plants accurate. Of animals, those of the land were most valuable. He spoke of the difficulty of correlation in some countries where vertebrate animals are not found in many of the deposits. Prof. Marsh agreed with the other speakers that vertebrate animals afforded the best and most accurate material for correlation. Prof. Charles D. Walcott spoke of the advances that had been made in the study of correlation, and illustrated his positions by reference to the Cambrian strata of North America. Prof. James Hall begged that geologists in search of correlations should not neglect physical methods, and described an early attempt at correlation made by himself in trying to connect the rocks of western New York with the deposits of the West.
By M. AMÉDÉE GUILLEMIN.
STRIKING discoveries in astronomy, of a character to excite the public mind, have been rare in recent years. Those who have kept in current with the work that has been done in that science are not ready to believe that this is because progress has not been made in it. As evidence of the new work accomplished by its students, and potentially fruitful work, too, we cite the preparation of a map of the sky, accomplished by the aid of photography, which gives the exact position of the stars to the fourteenth magnitude. The co-operation of observatories certainly assures the success of this immense work, which is now in process of execution. La Nature has made known the beginnings and has kept its readers in the current of the very minute and profound preliminary studies, without which the undertaking of operations of an extreme delicacy might have been compromised. It has also made clear the importance of the results to be obtained, and of the various consequences that would necessarily accrue from them. The problems of parallax or of stellar distances, of the proper motions of the stars, of nebulae, the search for minor planets and new comets, everything relative to the constitution of sidereal systems, may, by an attentive study of the plates of the new celestial maps, receive positive solutions. A new horizon is thus opened to science. These are not sensational novelties, like the appearance of a comet with a long, nebulous tail, which attracts the attention of idlers to the sky; but the importance of astronomical observations is not measured by the noise they make in the public ear. Yet, if the prize of a hundred thousand francs, which an honorable lady has recently bequeathed to the French Academy of Sciences, should be gained by some one, the resultant emotion would be legitimate. To establish voluntary and direct communication between the earth and a