50 ME. J. A. DOUGLAS ON GEOLOGICAL SECTIONS [April I914, 



EXPLANATION OF PLATES I-X. 



Plate I. 



Mount Taapaca (19,145 feet), seen from Putre. 



Plate LT. 

 Eastern entrance to the Jamiraya Gorge, Llutah River, near Patapatani. 



Plate ILL 



Fig. 1. Pillow-lava, Morro de Arica (Chile). 



2. Individual pillows embedded in Posidonomya Shales, at the same 

 locality. 



Plate IV. 



Fig. 1. Bedded rhyolites, tunnel (Kilom. 81), Arica-La Paz Railway. 

 2. Volcanic beds of the Mauri River (Bolivia). 



Plate V. 

 Intrusion of diorite through Cretaceous sandstones, Comanche (Bolivia). 



Plate VI. 



Chocolate-coloured sandstones and conglomerates of Permian age, east 

 fe of Comanche (Bolivia). 



Plate VLL 



Fig. 1. A 10 . Granodiorite invaded by acid magma ; Llutah River, near Cata 

 (Chile); showing hornblende (black) in process of solution by 

 quartz, and an irregular mosaic of quartz (clear) and felspar 

 (turbid). (In ordinary light, x 16 # 6 diameters.) See p. 17. 



2. The same between crossed nicols, X9'3 diameters. 



3. A 2 . Enstatite-andesite, pillow-lava ; Morro de Arica (Chile) ; augite 



(Au), enstatite (En), and plagioclase (andesine), with poly- 

 synthetic twinning, in an opaque ground-mass composed of 

 glass crowded with grains and skeleton- crystals of magnetite. 

 (Between crossed nicols, x8 diameters.) See p. 11. 



4. A 25 . Augite-andesite ; Mount Tacora (Chile) ; showing parallel arrange- 



ment of felspar- crystals (clear) with marginal zonary inclusions. 

 Pyroxenes (tinted) : augite and enstatite, in a hyalopilitic 

 ground-mass. (In ordinary light, X 9*3 diameters.) See p. 22. 



5. A 29 . Diorite ; Comanche (Bolivia) ; showing zonary structure of plagio- 



clase, and small idiomorphic crystals of hornblende. (Between 

 crossed nicols, X 8 diameters.) See p. 29. 



6. A 51 . Hornblende-augite-andesite ; River Cano (Bolivia); porphyritic 



crystals of plagioclase (PI) — andesine with Carlsbad twinning, 

 hornblende (Hb) twinned, and showing a resorption - border, 

 and augite (Au) with zonary structure, in a hyalopilitic ground- 

 mass. (Between crossed nicols, X8"6 diameters.) See p. 25. 



Plate VIII. 

 (All the figures are of the natural size.) 



Figs, la & lb. Macrocephalites sp., Callovian ; Morro de Arica, Chile. (See 



p. 9.) 

 2 a-2 c. Enteletes aff . hemiplicata Hall, Upper Carboniferous ; Arque, 



Bolivia. (See p. 35.) 

 3a-3c. Seminula ambigua Sow., mut. = jS. peruviana (D'Orb.), Upper 



Carboniferous ; Straits of Tiquina, Bolivia. (See p. 32.) 



