STRUCTURAL AND STRATIGRAPIIICAL RELATIONS 



447 



nently among them. The ferromagnesian (mafic) minerals are always 

 of smaller size than the feldspars. We have not found quartz among the 

 phenocrysts, and can safely state that it is, at most, rare. The rocks, 

 therefore, do not reach the percentages in silica characteristic of the 



SUPERFICIAL DEP0SIT6 



\irr:A\ RccENT- ffocJr Slides E 



SEDIMENTARY ROCHS IGNEOUS ROCHS 

 c/ferAceous 



Laccolitfi^Nal^NoZoAi. 



I \ P/F/.'iTocrf//'-C/oc,a/ Onfi \MEM y/rje/k ita^/e) S^nOsfone E^^ laccoAVIrs 



bi^^ Rt e/S TO COVE- C/ay eic. 

 UJ-:JJ QuArcffr^Affr- Terrace arave/s 



• t^-C-l MonTa.-na.-Ca.r^a.c/iarL 



Oi/Co. H^<L// /Yh/ 



• M-C-X <£o. iVe.// //o JL 



I ColoroJo forijjoiion 



5,/h 

 S DiAei 



I ; ~~1 Hooienat rormotion 



JU/f/IS3/C 

 l^. ~\ Ellts and Aforrjsort Fbrmai/um I ^f) 1 Spec/werj iocalii/e^ 



c/iffBONireffous ' 



Figure 3. — Oeological Map of West Butte 



rhyolite-granite series. Both orthoclase and plagioclase appear among 

 tlie phenocrysts. In some slides one predominates, in some the other. 

 It is improbable that, in any exposure of porphyritic rock, either one 

 absolutely fails, hut the orthoclase certainly sinks at times to a very small 



