GEOLOGICAL SURVEY OF THE TEREITOEIES. 85 



instances all tlie beds are inverted from the Silurian to tlie lignite 

 inclusive. 



Another interesting point I have reserved for discussion at a more 

 favorable time is the formation of canons and valleys of the rivers, 

 which enter into the scenery of the country as a most conspicuous fea- 

 ture. The fact that the streams seem to have cut their way directly 

 through mountain-ranges, instead of followiug synclinal depressions, 

 indicates that they began the process of erosion at the time of the com- 

 mencement of the elevation of the surface. This is shown all along 

 the valley of the Tellowstoue, and more conspicuously in theyalleya 

 of the Madison and Gallatin, which have carved immense canons or 

 gorges directly through two of the loftiest ranges of mountains in Mon- 

 tana. We believe that the course of these streams was marked out at 

 or near the close of the Cretaceous period, and as the ranges of moun- 

 tains were in process of elevation to their present height the erosion of 

 the channels continued. The details of the observations which con- 

 tribute to form this opinion would occupy a chapter or two. 



The superficial or drift deposits which some times attain a great thick- 

 ness are regarded as of local origin. As I have so often stated in my 

 j)revious reports, I have never been able to find any evidence in th 

 Eocky Mountain region of what is usually termed a northern drift. 

 There are many other points of great interest which, if time and oppor- 

 tunity occur in the years that are to come, we hope to treat as exhaust- 

 ively as our observations will permit, and we regret that we have not 

 been able to make more than a passing allusion to them in this report. 



The brief report of Hon. N. P. Langford, superintendent of the Yel- 

 lowstone National Park, who accompanied the Snake Eiver division, 

 will be read with great interest for its practical character. The thanks 

 ot the survey are extended to him, not only for the interesting and val- 

 uable report, but also for the great services he rendered the party while 

 on the route. The remarkable feat of Messrs. Stevenson and Langford 

 in ascending the Grand Teton, which will soon become familiar to the 

 reading public through the pages of Scribner's Monthly, will always 

 invest this region with an interest second only to the wonders of the 

 National Park. 



I had expected a valuable report from Mr. William Blackmore, who 

 accompanied the survey for several weeks as a guest. The survey is 

 under many obligations for most valuable services from this very liberal 

 and intelligent gentleman, and it is proud to regard him as one of its 

 four honorary members. It is probably due to Mr. Blackmore's absence 

 in Europe that we are deprived of his valuable views in regard to the 

 laying out of the park. 



I would also call attention to the report of Mr. Hering, which we hope 

 will be useful to railroad-men as well as to the general public. 



