DESCEIPTION OF THE PLATES. 203 



PLATE IX. 



Profiles from Big Horn mountains to near the Maricopas wells. 



Figure 1. a. Alluvium, desert sand, and deposit of Gila river ; G. Granitic basis of Big 

 Horn mountains ; / Metamorphic quartz and jasper rock, a conglomerate rock ; both 

 strata reposing on the granite and dipping southwest ; P. Intruding trachyte porphyry- 

 dyke ; D. Position of hills containing the vein of native copper ; 6. Table land capped 

 with basalt, and c, underlying calcareous sandstone. 



Figure 2. b. Basalt ; T. Trap dykes, communicating with the basalt overflow. The central 

 hill may be looked upon as the source whence the basalt flowed east and west over an 

 area of thirty-six miles wide. Other figures correspond to strata marked in section 1. 



Figure 3. Hills over which the trail runs, in the Jornada, to the Maricopas and Pimas vil- 

 lages : G. Central granitic axis, with veins of quartz q, containing titanium ore; and 

 /, dykes of felspar, crossing the quartz at right angles ; c. Desert conglomerate. 



PLATE X. 



Profiles from Pimas villages to entrance of the caiion of the Gila river. 

 Figure 1. a. Alluvium of Pimas plains; h. Basalt overflow; p. Isolated hill of protogine ; 



P. Porphyry dyke. This section is along the course of the river. 

 Figure 2. Profile of hill near camp, July 6. Basal rock is leucite, merging into trachyte. 



The capping is amygdaloid trachyte, overlying a coarse sandstone grit. 

 Figures. Ten mile profile along the Gila river, July 6 : a a a. Coarse porphyritic granite; 



b. Felspar rock ; c c c. Red felspar porphyry ; d. Basalt ; e. Augitic trap. 

 Figure 4. Profile of anticlinal axis entering the caiion : a. Primary rock, {vide section 5 ;) 



b. Yellow sandstone conglomerate ; c. Metamorphic sandstones ; d. Basaltic and trachyte 



lavas. 

 Figure 5. Structure of axial rock; a. Amygdaloid trachyte; b. Felspar and hornblende, 



a porphyritic rock ; c. Felspathic rock ; d. Basalt. 



PLATE XI. 



Profiles of the strata along the Gila where it canons to the mouth of the San Pedro river. 



Figure 1. a. Porphyritic jasper, beds running north and south — a stratified rock ; b. Thick 

 vein of sulphate of barytes ; d. Basalt dykes and overflow ; c. Syenitic mass in the am- 

 phibolic granite. 



Figure 2. Outline of the Spire hills, with distant lava capped hills north of the Gila; por- 

 tions of the Pinaleno hills. The Spire hills are of amphibolic granite, passing into 

 felspar, porphyry, and trachyte. 



Figure 3. Cross section of Spire hills, showing the summits formed of dykes of felspar, 

 which traverse the mass. 



Figure 4. a. Sandstone conglomerate on each side of the river, probably connected beneath ; 

 b. Porphyry conglomerate ; c. Lava capping ; d. Alluvial drift ; e. Felspar porphyry 

 and trachyte ; /. Granite. 



