268 UNIVERSITY OF COLORADO STUDIES 



• 



Fundamental Gneiss • 



Clear Creek Gneiss 



Binary Granite 



Central City Granite (Evans Granite) 



Troutdale Granite 



Diorite 



Pegmatite and Aplite 



Latite Porphyry 



Pleistocene and recent 

 The Fundamental Gneiss and Clear Creek Gneiss, while tolerably 

 distinct as areas, grade into each other at their boundaries, and the situa- 

 tion can be best described by a quotation from M 0710 graph XXVIII, U. 

 S. Geological Survey, on the Marquette Region, by W. S. Bayley. On 

 p. 151 he says: 



The foliated rocks occupy areas whose boundaries are not so well defined as is 



the case with the Marquette fragmentals Nevertheless, an attempt has been 



made to map these areas. In their interiors the different phases of schists, granites 

 and syenites are well characterized,. but on their peripheries there is always a complex 

 mixture of the various schists with one another or with the granite rocks. The 

 respective colors on the map are believed to cover the areas within which the cor- 

 responding rocks predominate largely over other rocks. The boundary lines separat- 

 ing the different areas are drawn at about the places the different varieties are found 

 in approximately equal quantities. 



And again from the Ashville Folio (Folio 116, p. 4) : 



In only a few cases do the boundaries shown on the map represent a single con- 

 tact between two large masses; they usually indicate a narrow zone beyond which 

 one rock or the other predominates. Sometimes an area shown as gneiss may con- 

 tain many small beds of granite, or it may be substantially all gneiss. * On the other 

 hand, many of the areas represented as granite include also small bodies of gneiss. 

 These may be continuous with one another or may be disconnected inclusions. 

 Except where these bodies were the prevalent rock over considerable areas, they 

 were disregarded in the mapping. 



It might be added for the whole Clear Creek district that one outcrop 

 may give examples of any or almost all of the hthologic units in question. 



It is well known that pre-Cambrian areas have a close resemblance the 

 world over. The lower Clear Creek area closely resembles other areas in 

 the United States that have been most closely studied, as, for example, 



