A. C. Peak— Age of the Rocky Mountains in Colorado. 179 



(Dakota Group) resting on the granite on both sides of the 

 Park* Following these outcrops farther north, in 1874, he 

 found both Jurassic and Triassic beneath the Cretaceous on the 

 granite, and on the west of the Park Eange the whole series of 

 sedimentaries is present, f Speaking of Miu- eP 

 " As was first distinctly pointed out by Newberry (Amer. 

 Assoc. Meeting, Newport. R. I. l?rSO, also later Proc. Amer. 

 Assoc, Aug., 1873, p. 185, etc.), east of the range, so here in 

 the Middle Park, the general aspect of the formation as a 

 whole is that of a ' circle of deposition,' an encroaching shore 

 line deposit of sandstones attending slow submergence, fol- 

 lowed by a deeper water sediment tunning slates and shales, 

 but not reaching sufficient depth or attaining the proper condi- 

 tions to develop extended limestone deposits; in turn followed 

 by a shallowing sea with more arenaceous accumulations." 

 The area of Middle Park, therefore, must have been above the 

 level of the Triassic sea, whose shore line was north of the 

 park but gradually encroaching on it, so that in Cretaceous 

 time the subsidence was sufficient to allow the deposition of the 

 Cretaceous rocks. 



Prof. Stevenson says, (p. 500), "It is probable that following 

 this upheaval [at the 'close of the Trias] ai 

 took place over our whole area to adi 

 the Cretaceous, which occurs not only o 

 all the old interior synclinal troughs 

 region. The close of the Cretaceous \ 

 disturbance throughout the greater porti 



the edge of the plains the dip of the rocks is from 10° to 20°, 

 though in some localities the action was excessive, ttirmne; the 

 strata on edge or pushing them over at Golden and the Garden 

 of the Gods. In South Park a well de6ned synclinal was pro- 

 duced." 



By referring to the sections in the Reports of the U. S. Geol. 

 Survey for 1873 and 1874, it will be seen that the Lower 

 Tertiary | is conformable to the underlying Cretaceous. In 

 South Park toward the northern end, in 1873, I found Lower 

 la resting on the granite toward the east.§ 

 What the relations were to the Cietaceous at the west I was una- 

 ble to determine on account of volcanic action. At - 

 along the . « .redo Bnrige, the Lo» 



overlaps the Cretaceous and rests on the granite. 1 In Middle 



t Unpublished geol. map'of Colorado, XJ. S. Geol. Survey. 



t Report TJ. S. Geol. Survey, p. 156. . T - ;tlp 



xtensive sul 





of the de|.o- 



dtion of 



he plains bu 



t along 



d in the so 



uthwest 



marked by 





of our area. _ 



Along 



