BNDLicH.l STRATIGRAPHY. 71 



to determine their geological position. The first group appears but 

 suborclinately in the district, but the Green Eiver covers a very large 

 area. It composes the entire mass of the Book Olifis, and extends 

 northward beyond White Eiver. A gentle northerly inclination of its 

 strata has produced the long, narrow ridges, separated by more or less 

 steep caiions. Readily eroded material composes the beds, and they 

 have offered but slight resistance to the action of water, and, in some 

 instances, ice combined. 



Gradually, as our knowledge of the Oenozoic formations of the Rocky 

 Mountains and contiguous areas increases, we are enabled to produce 

 a more definite, more acceptable classification. It is certainly a great 

 temptation to distinguish groups by local names, thus facilitating 

 description and geological chronology, but it leads to confusion, and 

 consequently to inferior value of the results obtained. It will be my 

 endeavor in the subjoined pages to correlate the facts observed witli 

 others already known, but to avoid, so far as consistent with the recog- 

 nition of these facts, the premature acce{)tance of any local subgroups. 

 In this way only can we eventually arrive at a comprehensive view of 

 the entire series of Oenozoic groups of the West. After once this series 

 has been well established, and its various members have been assigned 

 respectively to their proper positions, then, and no sooner, will be the 

 time to make subdivisions for the purpose of expressing systematic classi- 

 fication — the increased knowledge we have of the subject. Besides Ter- 

 tiary we find lake and drift deposits in the district. Tbe former are not to 

 be referred to any division of a special period, but merely represent the 

 ancient, perhaps not very remote, existence of lakes at certain localities. 

 Drift occurs as usually along the streams, and in some instances seems 

 to owe its present position to the action of glaciers. This will be dis- 

 cussed at greater length below. 



STKATIGEAPHY. 



In its general features the stratigraphy of our district is very simple. 

 We have, mainly, a westerly and then northerly dip of the strata, varied 

 only by local folds and flexures. Dr. White, whose district adjoins mine 

 on the north, has there found very important folds, forming continua- 

 tions of and connections witb others far distant. He Avill treat of them 

 fully in his report which is contained in this volume. At no point, ex- 

 cepting along the Hogback Ridge between the White and the Grand, 

 do any of the folds, observed farther north by him, extend into my dis- 

 trict, save for the distance of a few miles only. At the proper place 

 they will be discussed, so far as a discussion of mere fragments is possi- 

 ble. Here mention shall merely be made thereof as to the character and 

 locality of their occurrence. 



Following along the eastern side of *the Hogback Ridge we find that 

 a series of local disturbances have taken place; the most distant results, 

 probably, of serious and extensive folding and plication farther east. 

 They are, however, of but small dimensions, and the vertical dislocations, 

 produced have had but little influence in determining the configuration 

 of the region. As a rule, it may be stated that the strata dip westward 

 generally at an average angle of 8°. With the Hogback, however, we 

 find a Qliange. Along its northern end the dip is not much increased, 

 but travelling south we find that it grows steeper. At Station 5, on the 

 drainage of the Grand, the strata stand on end, gradually as'suming a 

 gentle dip again, farther west. This is one of those instances that have 

 so often been observed along the Front Range, where the dip in tbe imme- 



