248 Annals of the Carnegie Museum. 



tion, extending about two thousand miles eastward to the Allegheny- 

 Mountains, which, when compared with the Rocky Mountains, seem 

 merely like high hills and ridges. The change here is comparatively 

 sudden, and henceforth we shall be amidst very different scenes, the 

 result of different geological conditions. Though, we travel to the 

 Pacific coast, there will be no more uninterrupted level horizons, but 

 the dark silhouettes of the mountains will ever be seen against the back- 

 ground of the sky. 



If one enters the region for the purpose of learning its history, no 

 matter how faithfully one has studied geological literature, endless 

 difficulties will be encountered. Until one loses child-like faith in 

 the writers of text-books and geological theorists, one will not make 

 much progress. Facts must be observed at first hand, the observa- 

 tions of others must be refuted or confirmed, and theories must be 

 regarded as mere hypotheses to be confirmed or disproven. But 

 the student must not, on the other hand, go to the extreme of dis- 

 regarding the work of others. The geological conditions up to this 

 point, though they have been the subject of animated discussion and 

 difference of opinion among our best geologists and paleontologists for 

 half a century, are simple, compared with what lies before us, where 

 rocks of all ages have in some way gotten into all manner of positions, 

 and hardly a step in their vast history is settled beyond a doubt. The 

 observer must spend years in studying small phases of the great prob- 

 lem before his opinions can be of any great and permanent value ; and 

 even then he must expect that others will come after him and with the 

 accumulated knowledge, which time alone brings, improve on his 

 work. 



The rocks of the eastern slope of the Bridger-Gallatin Range are 

 principally of Cretaceous age. On the western slope the railroad de- 

 scends the East Gallatin River. The walls of the caiion are of Creta- 

 ceous and Palaeozoic rocks ; the latter appearing for the first time since 

 leaving Minnesota. The rocks of the massive Carboniferous lime- 

 stones, weathered into peculiar forms, extend in huge monuments and 

 rude castle-like forms high above the pine trees which surround their 

 bases. 



If we could pause for a while on the crest of the Bridger range a 

 little farther to the northward and look eastward, we would see a 

 wilderness of dissected ridges extending eastward and northeastward 

 to the high sharp peaks of the Crazy Mountains. To the westward at 



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