24G - I. EMMON OROGRAPHK MOVEMENTS, 



cially disturbed districts, where in the limited time at their command the 

 earlier explorers* of necessity overlooked or but imperfectly studied many 

 i importance in their bearing upon the general orographical history of 

 the region. Ii has been my lot during the past ten years to make a number 

 of such examinations, incidental tn a study of the ore deposits of important 

 mining districts in various part- of the Rocky Mountains in Colorado, and 

 thus gradually to gather together a Dumber <>i' tacts bearing upon this >ul>. 

 ject. Although these facts arc not sufficently complete for an exhaustive 

 discussion of the subject, I have been led to attempt to construct from them, 

 ami from such information derived from the work of others in the region 

 :i- -.-, med pertinent and trustworthy, a slight historical sketch of the oro- 



iphic movements of the Rock) Mountains between Archaean and Tertiary 

 times, with special reference to two important and hitherto not generally 

 lized movements, the one during the Carboniferous, the other during 

 the Jurassic epoch. 



Many of t lu* conclusions at which I had arrived have to a certain extent 

 been forestalled by my colleague, Dr. C. A. White, in his admirable add n 

 on the North American Mesozoic delivered at the last meetingof theAmeri- 

 can Association, at Toronto, Canada, but as they had Ween reached inde- 

 pendently and from a Boraewhat different standpoint I have not thought it 

 advisable on that account to modify what I had written. 



Before presenting this -ketch it may be well to review briefly the princi- 

 pal conclusions that have been arrived at by members of the various geo- 

 logical Burveys thai have examined this region. They will be taken as far 



:i» possible in the order in which the field work of each was done. 



Fortieth Parallel Survey.- -The orographic movements determined l>\ the 

 ilogists of the Fortieth Parallel Survey are given l»\ Mr. King ■ as fol- 

 low 



1. Post-Lauren tian, 



A ich.enll. 



r i' tic. 



I. Post Jurassic. 



I lUS. 



V' rmillion < In ek | Wasatch | Koc< ne 

 7. Post-G reen River Eocene. 

 r • Bridgi i cene. 



IK 



In. post Mini i ne 



II I ut"T I'll- ■ ic 



I 2. Post I'll" 



I ;. Paulte ■•: Lhi 1 1 ; • >i ical Period. 



■ 



