Professor Whitney communicated the following abstract of the results obtained by M. Rémond in his geological explorations of Northern Mexico, made in 1863 to 1865, and drawn up from his notes and specimens, after reference of the fossils obtained to Mr. Gabb and Dr. Newberry. M. Rémond has gone to Chili to continue his geological investigations, if his health permits; and he expects to write out a more detailed account of his Mexican work, whenever he has an opportunity of doing so. In the mean time, however, it is his desire that this abstract should be drawn up and published, that at least the more important results may be placed as soon as possible in the hands of those interested in the development of the geological structure of those countries which border on the Pacific coast. In presenting this paper, Professor Whitney desired to express his admiration of the courage and endurance with which M. Rémond had prosecuted his investigations in Mexico, where he had to contend with every kind of difficulty and danger, but where, however, he had obtained results of great value, throwing the first rays of light on the age of the formations of a very interesting and economically important mining region—a region which has been often visited, but where, previous to M. Rémond’s examinations, no positive evidence of the geological position of any of the stratified rocks had been obtained, and no clue given to the relations of the metalliferous veins to each other, or to the rocks in which they are inclosed. Notice of Geological Explorations in Northern Mexico. BY A. RÉMOND. [Compiled from his notes, and prepared for publication, by J. D. Whitney.] 1. PRELIMINARY REMARKS. The mountainous region comprising the central and western portion of Northern Mexico, belongs to the four States of Durango, Chihuahua, Sinaloa, and Sonora. Considering how celebrated this portion of Mexico has become for its mines and metalliferous veins, and how much has been written about it, it is surprising how little exact information has hitherto been obtained with regard to either its geography or geology. On comparing the principal published maps[21] of the region in question, it will be seen at once how much they differ from each other in their delineations of even its main topographical features, while the details are entirely wanting.