INTRODUCTION. 



EXCURSION TO Tin: ROOKY MOUNTAINS. 



The undersigned was called upon, a tew weeks before the opening of 

 the Congress, to prepare a geological guide book for the use of those 

 members of the Congress who should take part in the proposed excur- 

 sion to the Rocky .Mountains. 



Parts of the vast region to be passed over during the excursion had 

 never been systematically examined; of other parts the results of recent 

 examinations had not yet been published, and the published Surveys of 

 still other parts were scattered through many bulky Government, State, 

 and other reports, all of which it would have been impossible to consult 

 in the time given, and many of which had been more or less superseded 

 by later and as yet unpublished observations. Under these circum- 

 stances the only feasible plan for preparing such a guidebook was to call 

 Upon geologists within reach, who were most familiar with different parts 

 of these regions, to contribute descriptions of the geology of such parts. 

 Those thus called upon responded most promptly and generously, but 

 their contributions necessarily varied somewhat in detail and method of 

 treatment, according to the varying conceptions of the authors. It 

 was not possible, in the limited time given, to return their manuscripts 

 to the authors for revision so as to produce the necessary uniformity, 

 and the duty therefore fell upon the editor of hastily rewriting a con- 

 siderable portion of the material contributed, and of tilling in any gaps 

 to the best of his personal knowledge. The resulting guide book was 

 necessarily somewhat unequal in the amount of detailed description 

 given of different parts of the region, and also incomplete in illustration 

 and bibliographic reference In spite of these imperfections, it so well 

 subserved its purpose that a unanimous request was made by the other 

 secretaries, who had taken part in the excursion, that it should be pub- 

 lished in the Oompte-rendu, after revision by the various contributors 

 of the parts for which they were to be held responsible, and the addition 

 of as many illustrations and bibliographic references as possible. This 

 request has been complied with, as far as has proved practicable, in the 

 following pages. In a few cases the original contributors have been 

 too busy to revise their notes, and the editor has been obliged to pre- 

 sent the description of their regions much as they originally appeared. 

 In other cases, where the descriptions contained in the original guide 



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