A. G. Peak — Age of the Rocky Mountains in Colorado. 173 



terior* no rock of more recent origin than the Carboniferous is 

 involved in the main axes." Again he says, (p. 495) : " In the 

 main portion of this second group (including Blue Eiver Range, 

 Park Range, Samnv >le Cristo and Spanish Range, and Ar- 

 kansas or Saguache (Sawatc/t) Range, see pp. 490, 491,) no 

 rocks occur of later date than the Carboniferous, which with 

 riving Silurian maybe traced along the eastern face 

 to the Blue River." 



On the west side of South Park, the sedimentary forinatioii.-f 

 are present from the Primordial to the top of the Cretaceous, 

 all conformable and dipping to the eastward, extending from 

 the summit of the Park Range eastward into South Park. I 

 grant that on the summit and slopes of the Range, the entire 

 series is not seen, but simply because the range has been sub- 

 jected to erosion. Al 3 nan beds are seen 

 and at others both Silurian and Carboniferous. Commencing 

 at the summit of the range and going eastward into the Park, 

 we find, with the exception of faulting in the Carboniferous 

 and Silurian strata, which probably occurred in Post Cretaceous 

 time that t ied each other in regular order. 

 The sequence is uninterrupted. It is true that when we com- 

 pare the dip of the Carboniferous rocks on the range, with the 

 dip of the Cretaceous out in the park, that it is not precisely 

 the same, but we must remember that the outcrops are three or 

 four miles apart. The inclination in both cases is in the same 

 din . n Hid if the Cretaceous beds were continued to the sum- 

 mit of the Range as they did originally, we should find them con- 

 formable to the Carboniferous; and" were we to sink a shall at 

 the base of the Cretaceous outcrop in the Park, we should 

 doubtless note the conformability of the Cretaceous with the 

 underlying Paleozoic strata. When we cross the upturned 

 edges of the strata we find no uncomformability.^ 



Crossing the Park Range to the Arkansas Valley, we find 

 <io sedimentary beds on the eastern front of the Sawatch 

 Range. As pointed out bv Dr. Hayden§ and myself | in 1873, 

 the sedimentaries of the Park Range once extended unrnter- 

 ige, but have been removed by 

 erosion. Prof. Stevenson is hi ilol >- He 



says (p. 492) : " It is clear then that the Paleozoic rocks, the 

 same with those found on the Park Range, at one time reached 

 unbroken from South Park to the Arkansas or S 

 {tiauxtich) Range. How terrible was the erosion which not 



e Report of U. S. Geol. Sur 



