part 1J THROUGH THE ANDES OE PERU AND BOLIVIA. 53 



main Cordilleras, which was accompanied by the intrusion of 

 rocks of ' calcic ' type. 



The continuation of the Jurassic zone of the Morro de Arica and 

 the Llutah and Palca Valleys, lies hidden beneath the desert sands 

 of the Pampa de Clemesi and the Pampa de Islay, an occasional 

 outcrop of barren quartzite on the foot-hills of Cachendo and in 

 the neighbourhood of Pamal being provisionally regarded as the 

 remnants of a formerly extensive Mesozoic cover. Jurassic strata, 

 which proved to be of Bajocian age, were discovered, however, 

 much farther inland at Lagunillas, and are probably also repre- 

 sented by the cpiartzites of -the Sumbay district. 



The granitic rocks which form the batholitic core of the Jami- 

 raya district in Northern Chile, were found to be continued in the 

 Palca and Moquegua Valleys, and once more reappear to form the 

 Cachendo foot-hills and the Cerros de la Caldera near Arequipa. 

 The plutonic complex here comprises at least three phases of 

 deep-seated intrusion, represented by the granodiorite of Cachendo 

 and Quishuarani, the augite-diorite of Huaico, and the adamellites 

 of Huagri and Tiabaya. 



An interesting example is described of the progressive dynamic 

 metamorphism of a coarse-grained plutonic rock into a tine-grained 

 gneiss. A characteristic feature of the district is the almost com- 

 plete absence of tourmaline-bearing veins, which are so abundantly 

 associated with the granodiorites of the south. 



The line of giant volcanic peaks, which forms the outstanding 

 feature of the Western Cordillera of Northern Chile, is continued 

 into Peru, where Mount Pichu-Pichu, El Misti, and Chachani are 

 seen as an imposing panorama from Arequipa. Many of the 

 augite- and hornblende-andesites found in the neighbourhood of 

 the cones, are of very similar character to those described from 

 Mount Taapaca and Tacora. The volcanic outbursts, however, 

 have chiefly given rise to rocks of a pyroclastic nature, and a 

 wide stretch of country, comparable with that of the Mauri-River 

 district of Bolivia, lies buried beneath a thick mantle of pumiceous 

 tuff. 



The red Cretaceous marls of the Coro Coro district, with their 

 deposits of rock-salt and gypsum, are here represented by grey 

 cherty limestones, evidently laid down in more open waters. These 

 limestones are almost devoid of fossils ; they are in places much 

 dolomitized, and pass laterally into marls, when they have the 

 appearance of reef -knolls. The transgressive character of the beds 

 is very clearby displayed. At Lagunillas they rest horizontally, 

 with a thick basal conglomerate, on strongly-folded Jurassic rocks, 

 while farther east they overlie with marked unconformity the 

 Devonian beds of Taya Taya. 



The post- Cretaceous line of dioritic intrusion, formerly described 

 as running through Coro Coro and Comanche in Bolivia, once more 

 appears along the line of section at Maravillas ; the mineralogical 

 character of the rock is almost identical in the two areas, 

 although in the present case it appears to have been somewhat 



